ACID-BASE

As the bricks are heated, gases are given off. For example, carbon dioxide and sulphur dioxide are generated in the kiln. The major problem associated with the emission of these oxides is that they A. B. C. D.

lower the available water in the atmosphere may combine with water to produce acid rain lower the available oxygen in the atmosphere have a cumulative effect in the food chain (biomagnification)

Use the following information to answer the next two questions. Caustic soda solution, NaOH(aq), is very corrosive and must be handled with care. A caustic soda spill could be neutralized with acetic acid, CH3COOH(aq). NaOH(aq) + CH3COOH(aq)  NaCH3COO(aq) + H2O(l) H = 56.1 kJ/mol 3.

The energy diagram that represents the complete neutralization of 50.0 mL of 2.00 mol/L caustic soda solution with acetic acid is

E p (kJ)

A.

The chlor-alkali process used by Dow Chemical in Fort Saskatchewan uses sodium chloride from underground deposits. The sodium chloride is dissolved in water and then pumped into electrolytic cells where a current is passed through the solution to form yellow chlorine gas, colourless hydrogen gas and aqueous sodium hydroxide. The ionic equation is

E p (kJ)

C.

Numerical Response

The pH of a 0.20 mol/L NaOH(aq) solution is ________. (Record your answer to three digits).

The best laboratory method that can be used to determine the concentration of a solution of NaOH(aq) is A. C.

titration calorimetry

B. D.

distillation extrapolation

5.

Reaction coordinate

5.61

5.61 Reaction coordinate

In the reaction, a Brønsted-Lowry conjugate acid-base pair is A. B. C. D.

Caustic soda, NaOH(aq), is also produced during the electrolysis of NaCl(aq).

70.1

D.

Reaction coordinate

4.

2.

70.1

Reaction coordinate

2H2O(l) + 2Na+(aq) + 2Cl-(aq)  Cl2(g) + 2Na+(aq) + 2OH-(aq) + H2(g)

1.

B. E p (kJ)

The manufacturing of brick and ceramic products is an important industry in Alberta. High quality clay and sand from quarries in the Cypress Hills are processed in Medicine Hat.

E p (kJ)

1.

CH3COOH(aq) and CH3COO-(aq) CH3COOH(aq) and OH-(aq) CH3COOH(aq) and H2O(l) CH3COO-(aq) and H2O(l)

A chemical equilibrium system is always characterized by A. B. C. D.

the presence of equal amounts of reactants and products the completion of a chemical reaction when changes cease to occur equal amounts of reactants and products entering and being removed from the system the conversion of reactants to products occurring at the same rate as the conversion of products to reactants

Numerical Response 2.

1 2 3 4

lime juice salmon apple cider egg white

Numerical Response [OH-(aq)] [H3O+(aq)] [OH-(aq)] [H3O+(aq)]

= = = =

7.7 x 10-13 mol/L 6.3 x 10-7 mol/L 1.3 x 10-11 mol/L 3.0 x 10-8 mol/L

3.

Al(H2O)63+(aq) + H2O(l) Al(OH)(H2O)52+(aq) + H3O+(aq) Ka = 1.4 x 10-5

When these foods are listed from most acidic to least acidic, the order is __________. (Record all four digits.)

6.

7.

0.16 mol/L 0.41 mol/L

B. D.

9.

0.25 mol/L 0.65 mol/L

Kelly tested portions of a solution with three indicators to determine the approximate pH Indicator bromocresol green indigo carmine thymophthalein

A student sampled four different acids, each at 0.10 mol/L, and she recorded these observations. Acid I Acid II Acid III Acid IV

Volume (mL) 50.2 40.5 20.7 15.0

pH 4.50 3.25 1.50 5.50

Conductivity poor poor good poor

The acid that would be expected to have the lowest Ka value would be A. C. 8.

If [Al(H2O)63+(aq)] = 0.150 mol/L, the pH of the system at equilibrium is __________. (Record your answer to three digits.)

A solution of hydrocyanic acid has a pH of 4.80. The concentration of the HCN(aq) solution is A. C.

Manufacturers used to add alum during the production of paper. The aluminum ion in alum is hydrated, and the following equilibrium established:

Acid I Acid III

B. D.

Acid II Acid IV

The approximate pH of the solution is A. C.

C. D.

most acids can act as oxidizing agents an oxidizing agent donates electrons and acts like an acid the base in an acid-base reaction acts like a reducing agent there is a transfer of a charged particle in both

5.0 10.8

B. D.

9.0 11.6

Numerical Response 4.

Four test tubes each contain 10.0 mL of 0.10 mol/L HCl(aq). Each test tube also contains a different indicator as listed below:

The Brønsted-Lowry theory of acids and bases is similar to redox theory in that A. B.

Colour blue blue blue

Test tube 1 2 3 4

Indicator indigo carmine thymol blue methyl red methyl orange

One drop of 0.10 mol/L NaOH(aq) is added to each test tube, and the colour is noted. A second drop of NaOH(aq) is added to each test tube, and colour is again observed. The same procedure is repeated until all solutions are yellow. In what order did the solutions in the test tubes turn yellow? __________ (Record all four digits.)

10. The volume of 0.100 mol/L NaOH(aq) required to neutralize 1.00 L of a strong monoprotic acid solution with a pH of 3.000 is A. C.

10.0 mL 1.00 L

B. D.

333 mL 3.00 L

11. Which species is not amphiprotic? A. C.

H2O(l) NH4+(aq)

B. D.

A problem of global concern is acid deposition, more commonly referred to as acid rain. Some acidity in rainwater is normal due to the dissolving of atmospheric carbon dioxide, but the minimum pH value that can be attributed to this is 5.6. Much lower pH values have been measured in rain and snow in many parts of the world. This drop in pH is primarily caused by the burning of fossil fuels, which releases oxides of sulphur and nitrogen into the atmosphere.

HS-(aq) H2BO3-(aq)

12. Which acid is not polyprotic? A. C.

HOOCCOOH(aq) H2SO3(aq)

B. D.

HCOOH(aq) H3PO4(aq)

13. When a small volume of a strong acid is added to a buffer, the pH of the solution should A. B. C. D.

increase decrease remain constant increase first and then decrease

14. Much of the carbon dioxide in the human body is transported on the hemoglobin molecule rather than dissolved in blood because the carbon dioxide would react with the water to form A. B. C. D.

a basic solution, increasing the pH of the blood an acidic solution, increasing the pH of the blood a basic solution, decreasing the pH of the blood an acidic solution, decreasing the pH of the blood

16. Cars today are smaller, more fuel-efficient, and operate at higher engine temperatures than cars in the past. A disadvantage of this from an ecological perspective is that A. cars cost more to maintain B . cars release more CO2(g) into the atmosphere C. at higher engine temperatures more NO(g) is produced D. less fuel consumption results in layoffs in the energy sector 17. In 1974, a sample of rain in Scotland was analyzed and found to have a pH of 2.20. The pOH and the hydroxide ion concentration in this sample were A. B. C. D.

15. Titration of an Unidentified Base

11.80 and 6.3  10-3 mol/L 11.80 and 1.6  10-12 mol/L 2.20 and 6.3  10-3 mol/L 2.20 and 1.6  10-12 mol/L

14 12 10 pH

8 6

Treasures found in sunken Spanish galleons sometimes contain silver coins in wooden chests. After many years under water, these coins become coated through the following sequence of chemical reactions:

4 2 0

0

25 50 75 Volume of nitric acid (mL)

100

I 125 II III

Which indicators can be used to accurately estimate the first and second equivalence points? A. B. C. D.

thymolphthalein - methyl orange thymolphthalein - thymol blue alizarin yellow - thymol blue all of the above

2 Ag(s) + H2S(aq)  Ag2S(s) + H2(g) 150 CO2(aq) + 2 H2O(l) HCO3-(aq) + H3O+(aq) 2+ Ca (aq) + HCO3 (aq) + H2O(l) CaCO3(s) + H3O+(aq)

18. Reaction I resulted in A. B. C. D.

an increase in the pH as a decrease in the pH as an increase in the pH as a decrease in the pH as

H2(g) was produced H2(g) was produced H2S(aq) was consumed H2S(aq) was consumed

9.

The Ka expression for reaction II is

22. An acidic solution was titrated with NaOH(aq) and the points were plotted below.

[HCO3(aq) ] [H3O (aq) ] [CO2(aq) ] [H2O(l) ] +

Ka =

B . Ka =

[HCO3-(aq) ] [H3O [CO2(aq) ]

+ (aq) ]

[CO2(aq) ] [H2O(l) ]

C.

Ka =

D.

Ka = [HCO3-(aq)][H3O+(aq)]

[HCO3-(aq) ] [H3O +(aq) ]

20. The limestone, CaCO3(s), that would eventually cover the silver coins could be removed by A. B. C. D.

adding a basic solution decreasing the pH of the system adding sodium hydrogen carbonate solution increasing the pressure on the system

pH

A.

14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 0

21. Technicians periodically check the concentration of NaOH(aq) in the chlor-alkali cells. In one test, a 10.0 mL sample of the solution required 44.9 mL of 0.850 mol/L HCl(aq) to reach the end-point.

50 (mL)

75

The best choice of indicator for this titration is A. B. C. D.

The Dow Chemical site at Fort Saskatchewan produces large quantities of chemicals for use in industry. On this site there are two chlor-alkali plants that produce chlorine and other byproducts. The chlor-alkali process involves the electrolysis of NaCl(aq).

25 Volume of NaOH(aq)

orange IV indigo carmine phenolphthalein chlorophenol red

23. If some NaOH(aq) was spilled, the spill could be neutralized by the addition of NaHSO4(aq). The net ionic equation for this reaction is A. OH-(aq) + H3O+(aq) 2 H2O(l) B . OH-(aq) + HSO4-(aq) H2O(l) + SO4-(aq) C. NaOH(aq) + NaHSO4(aq) H2O(l) + Na2SO4(aq) D. 2 Na+(aq) + OH-(aq) + HCO3-(aq) H2O(l) + 2 Na+(aq) + CO32-(aq)

The concentration of NaOH(aq) in the sample was A. C.

0.189 mol/L 3.82 mol/L

B . 0.695 mol/L D. 5.28 mol/L

24. One condition of a system at equilibrium is that the A. reaction proceeds to completion B . concentration of products and reactants are equal C. rate of the forward reaction does not equal the rate of the reverse reaction D. concentration of reactants and products undergoes no change

10

25. The equation that best represents the system of solid ammonium chloride in equilibrium with ammonia gas and hydrogen chloride gas is A. B. C. D.

29.

NH4Cl(s) + NH3(g) HCl(g) + N2(g) + 3 H2(g) NH3(g) + HCl(g) NH4Cl(g) NH4Cl(s) + HCl(g) NH3(g) + H2(g) + Cl2(g) NH4Cl(s) NH3(g) + HCl(g)

A. C.

diprotic weak acid diprotic strong acid monoprotic weak acid monoprotic strong acid

6.

Students subjected six solutions to conductivity and litmus paper tests and obtained these results.

Solution 1 2 3 4 5 6

Conductivity good poor good none good poor

1

products are favoured CH3COO-(aq) is an acid SO42-(aq) is a proton donor HSO4-(aq) and CH3COOH(aq) are a conjugate acid-base pair

28. Brønsted-Lowry theory defines acids as substances that accept protons increase the [H3O+(aq)] turn blue litmus red donate protons

2

Al(OH)(H2O)52+(aq) + H3O+(aq) 3

4

Ka = 1.4  10–5 In the forward reaction, the Brønsted-Lowry acid is ___. (Record your answer in the first column.)

Litmus Paper Test Red Blue red blue blue blue red red red blue blue blue red red

27. In the acid-base reaction CH3COO-(aq) + HSO4-(aq) CH3COOH(aq) + SO42-(aq),

A. B. C. D.

B . Thymol blue D. Phenolphthalein

Manufacturers used to add alum, Al 2(SO4)3(s), during the production of paper. The aluminum ion was hydrated and the following equilibrium was established:

Al(H2O)63+(aq) + H2O(l)

In the forward reaction, the Brønsted-Lowry base is ___. (Record your answer in the second column.) In the reverse reaction, the Brønsted-Lowry acid is ___. (Record your answer in the third column.)

The solutions that are not acids, in ascending numerical order, are __________. (Record all four digits.)

A. B. C. D.

Orange IV Methyl orange

Numerical Response

Numerical Response 5.

Colour yellow yellow red pink

For which indicator is the colour correct in 0.10 mol/L HCl(aq) solution?

26. Sulphuric acid is a A. B. C. D.

Indicator orange IV thymol blue methyl orange phenolphthalein

In the reverse reaction, the Brønsted-Lowry base is ___. (Record your answer in the fourth column.)

30.

HCl(aq) is added to a neutral solution containing bromothymol blue indicator. Which changes to the solution would you expect? [H3O+(aq)] increases, pH decreases, colour becomes more yellow B . [H3O+(aq)] increases, pH increases, colour becomes more yellow C. [OH-(aq)] increases, pH decreases, colour becomes more blue D. [OH-(aq)] decreases, pH increases, colour becomes more blue A.

Numerical Response 7.

An important buffer in blood is the H2CO3(aq) / HCO3-(aq) system. The equilibrium for this buffer is H2CO3(aq) + H2O(l)

H3O+(aq) + HCO3-(aq)

A sample of this buffer at equilibrium contains 1.1  10-4 mol/L HCO3-(aq) and 1.2  10-5 mol/L H2CO3(aq). The pH of the sample is __________. (Record your answer to three digits.)

31.

Champagne is mixed with orange juice and served at “Champagne Breakfasts.” Orange juice contains sufficient hydronium ions to kill a human if blood were not buffered. One of the buffers in blood is the H2PO4-(aq) / HPO42-(aq) system. When a small amount of acid from the beverage enters the bloodstream, the pH is maintained by this buffer because the H3O+(aq) reacts with A. B. C. D.

H2PO4-(aq) H2PO4-(aq) HPO42-(aq) HPO42-(aq)

to produce to produce to produce to produce

HPO42-(aq) H3PO4(aq) H2PO4-(aq) PO43-(aq)

32. Air bags are designed to deploy when a car moving in excess of 18 km/h undergoes a sudden decrease in speed. During the deceleration, an electrical circuit ignites a small amount of explosive powder to cause sodium azide, NaN3(s), to react inside the air bag. The sodium azide rapidly decomposes, producing nitrogen gas, which fills the bag. The equation for this reaction is 2 NaN3(s)  3 N2(g) + 2 Na(s) + 43.5 kJ. One problem associated with inflated air bags is that a white powder is produced. It can cause skin and eye irritation. This irritation is most likely due to the sodium metal reacting with moisture in the surroundings to form A. B. C. D.

an acid a base a salt an inert, gritty material

In a car engine, NO(g) can form. Once released into the air, NO(g) can react with oxygen and water to produce acid rain. Reaction I: N2(g) + O2(g) 2 NO(g) Reaction II: 2 NO(g) + O2(g) 2 NO2(g) Reaction III: 2 NO2(g) + H2O(l) HNO3(aq) + HNO2(aq)

33. The equilibrium expression for reaction II is A.

Keq =

B . Keq =

C.

Keq =

D.

Keq =

2[NO(g) ] [O2(g) ] 2[NO2(g) ]

[NO(g) ] 2 [O2(g) ] [NO2(g) ] 2 2[NO2(g) ]2 [NO(g) ]2 [O2(g) ]2 [NO2(g) ]2 [NO(g) ]2 [O2(g) ]

34. A student knows that as more NO(g) is produced in the endothermic reaction I, more acid rain forms as a result of reaction III. If the temperature of a car engine is increased, the amount of HNO3(aq) and HNO2(aq) produced in reaction III will A.

decrease because the reaction I equilibrium shifts to the left B . decrease because the reaction I equilibrium shifts to the right C. increase because the reaction I equilibrium shifts to the left D. increase because the reaction I equilibrium shifts to the right

Fritz Haber was awarded the Nobel Prize in 1918 for his development of a process capable of synthesizing ammonia. The Haber process involves injecting hydrogen and nitrogen into a heated reaction vessel. The overall reaction involved is N2(g) + 3 H2(g)

A. C.

2.2 9.5

B . 4.5 D. 11.8

2 NH3(g) + heat. 38. Which of the following is a correct statement concerning an aqueous solution?

Use the following information to answer the next two questions. An experiment designed to investigate this reaction yielded the data plotted below. 9 8

A. B. C. D.

As [H3O+(aq)] increases, [OH–(aq)] decreases. As [H3O+(aq)] increases, [OH–(aq)] increases. As pH increases, [OH–(aq)] decreases. As pH increases, [H3O+(aq)] increases.

39. The Kb value for the conjugate base of hypochlorous acid is

7

Concentration (mol/L)

37. Household ammonia is a cleaning product in which the concentration of ammonia is about 2 mol/L. The pOH of a 2 mol/L ammonia solution is

6 nitrogen

5

hydrogen ammonia

4 3

A. C.

2.9 x 10–6 6.8 x 10–8

B . 3.4 x 10–7 D. 7.1 x 10–9

40. The value for Kw

2 1 0 0

1

2

3

4

5

6

7

Time (min)

35. At what time was equilibrium first reached in this experiment? A. C.

0.0 min 3.0 min

B . 1.5 min D. 6.5 min

Use the value selected for Multiple Choice 35 to answer Numerical Response 8.

A. is equal to the [H3O+(aq)][OH–(aq)] B . changes depending on the pH C. shows that adding OH–(aq) increases the [H3O+(aq)] D. shows that the [OH–(aq)] can never be less than 1.00  10–14 mol/L 41. A 0.100 mol/L unknown acid solution is found to have a [H3O+(aq)] equal to 0.0015 mol/L. The pH of this acid solution is A. C.

1.00 3.82

B . 2.82 D. 13.00

42. A substance may be classified as: Numerical Response 8.

I. II. III. IV.

The Keq for this reaction is __________. (Record your answer to three digits.) ---------------

an acid a base an oxidizing agent a reducing agent

According to redox theory and Brønsted-Lowry theory, water can be classifed as 36. The value of the equilibrium constant for this system will change if the system is subjected to a change in A. C.

volume temperature

B . pressure D. concentration

A. C.

I and III only I and IV only

B . II and III only D. I, II, III, and IV

43. The conjugate acid of H2BO3–(aq) is A. C.

HBO32–(aq) H2O(l)

49.

B . BO33–(aq) D. H3BO3(aq)

44. The hydrogen sulphide ion, HS–(aq), is

Indicator

Colour in Unidentified Solution

orange IV methyl red phenol red phenolphthalein

yellow orange yellow colourless

The pH of the unidentified solution is approximately A. B. C. D.

the conjugate acid of hydrosulphuric acid an amphoteric/amphiprotic species a weak acid and a strong base a proton donor only

45. Equal volumes of two solutions that contain equal concentrations of HCO3–(aq) and H2PO4–(aq) are mixed. In the reaction between H2PO4–(aq) and HCO3–(aq), the substance that acts primarily as an acid is A. C.

H2PO4–(aq) HPO42–(aq)

B . HCO3–(aq) D. H2O(l)

46. The first equilibrium established when phosphoric acid ionizes in water is A. H3PO4(aq) + 3 H2O(l) 3 H3O+(aq) + PO43–(aq) B . H3PO4(aq) + H2O(l) H2PO4–(aq) + H3O+(aq) C. H3PO4(aq) + 2 H2O(l) HPO42–(aq) + 2 + H3O (aq) D. H3PO4(aq) 3 H+(aq) + PO43–(aq) 47.

Acid

Ka

H2O(l) H2S(aq) H2Se(aq)

1  10–14 1.1  10–7 1.7  10–4

The predicted Ka value of H2Te(aq) would be A. less than the Ka for H2O(l) B . greater than the Ka for H2O(l) but less than the Ka for H2S(aq) C. greater than the Ka for H2S(aq) but less than the Ka for H2Se(aq) D. greater than the Ka for H2Se(aq) 48. In which 0.10 mol/L solution would bromothymol blue turn green? A. C.

NaOH(aq) NaCl(aq)

B . K2CO3(aq) D. HOOCCOOH(aq)

A. C.

3.0 6.2

B . 5.2 D. 8.0

50. In a titration experiment, a student finds that 14.00 mL of NaOH(aq) are required to neutralize 0.93 g of monoprotic potassium hydrogen phthalate, KHC8H4O4(s). The concentration of the base is A. C.

0.00033 mol/L 0.33 mol/L

B . 0.064 mol/L D. 3.1 mol/L

51. The control of blood pH is important to the transport and delivery of oxygen in the bloodstream. Some important reactions that occur in the circulatory system are: I. II.

HHb(aq) + O2(g) hemoglobin HHbO2(aq) + HCO3–(aq)

HHbO2(aq) oxyhemoglobin H2CO3(aq) + HbO2–

(aq)

III.

H2CO3(aq)

CO2(g) + H2O(l)

Each of these reactions can affect the others. When there is a high concentration of O2(g) in the lungs, the effect would be to shift A. B. C. D.

reaction I right and reaction II left reaction I right and reaction III left all three reactions left all three reactions right

56. The Brønsted–Lowry equation that best represents the equilibrium in an aqueous solution of ammonia is Nitrogen fixation occurs slowly in the atmosphere. The equation for this reaction is N2(g) + O2(g) + 180.4 kJ

2 NO(g) Keq = 4.0  10

–31

at 25.0°C

52. The equilibrium expression for this reaction is

A.

Keq =

C.

Keq =

A. B. C. D.

2[NO(g) ]

B . Keq =

[N2(g) ] [O2(g) ] [N2(g) ] [O2(g) ]

D.

2[NO(g) ]

Keq =

57. A catalyst is utilized in the Haber–Bosch process because the

[NO(g) ]2

A. B. C. D.

[N2(g) ] [O2(g) ]

[N2(g) ] [O2(g) ] [NO(g) ]2

NH3(aq) 3H+(aq) + N3–(aq) NH3(aq) + H2O(l) NH4OH(aq) NH3(aq) + H2O(l) NH4+(aq) + OH–(aq) NH3(aq) + H2O(l) H3O+(aq) + NH2–(aq)

reaction is exothermic heat of formation of ammonia is high mole ratio of the reactants is 1:3 reaction is slow

58. The conditions that theoretically favour the formation of ammonia in the Haber–Bosch process are

53. Equilibrium has been achieved when the A. total pressure does not change B . rate of the forward reaction equals the rate of the reverse reaction C. rate of the forward reaction is twice that of the rate of the reverse reaction D. total energy changes 54. At equilibrium, if the [O2(g)] = [N2(g)], then A. C.

[NO(g)] = [N2(g)] [NO(g)] = 2 [N2(g)]

B . [NO(g)] > [N2(g)] D. [NO(g)] < [N2(g)]

A. B. C. D.

high pressure and high temperature high pressure and low temperature low pressure and high temperature low pressure and low temperature

Use the following information to answer the next two questions. The overall reaction in the Haber–Bosch process for the production of ammonia is N2(g) + 3 H2(g)

2 NH3(g).

Data for this equilibrium system was collected and plotted on a graph by a student. 5.00

N2(g) + 3 H2(g)

2 NH3(g) + 92.2 kJ

55. In aqueous solution, ammonia is a A. B. C. D.

weak base strong base weak triprotic acid weak monoprotic acid

4.00

Concentration (mol/L)

Large quantities of ammonia are produced by the Haber–Bosch method. The essential reaction in this process involves the equilibrium

3.00

nitrogen

2.00

ammonia

1.00

hydrogen

0.00 0.00

1.00

2.00

3.00

Time (min)

4.00

5.00

Numerical Response The minimum time, in minutes, required to establish equilibrium is ________ min. (Record your answer to three digits.)

9.

61. The sketch that indicates the change that occurs when 1.0 mol/L HNO3(aq) is added to 20 mL of 1.0 mol/L NH3(aq) is

Numerical Response 10.

The equilibrium constant for this system is __________. (Record your answer to three digits.) ---------------

59. The hydrogen used in the Haber–Bosch process is produced by CH4(g) + H2O(g)  CO(g) + 3H2(g). If 1.00 t of H2(g) is required daily, then the mass of CH4(g) required, assuming 100% reaction, is A. C.

0.333 t 7.95 t

Use the following information to answer the next two questions. Nitric acid is used in the production of ammonium nitrate, NH4NO3(s), an important fertilizer. The equations for its production are HNO3(aq) + NH3(aq)  NH4+(aq) + NO3–(aq) NH4+(aq) + NO3–(aq) + heat  NH4NO3(s)

I. II.

60. Aqueous solutions of ammonium nitrate are acidic. A 0.20 mol/L solution of NH4NO3(aq) would have a pH of A. C.

0.70 4.97

---------------

B . 2.65 t D. 23.8 t

B . 4.47 D. 5.12

62. A cleaning agent has a pH of 1, and a carbonated beverage has a pH of 5. The cleaning agent is more acidic than the carbonated beverage by a factor of A. C.

10 000 100

B . 1 000 D. 10

Numerical Response Use the following information to answer the next two questions.

11.

pH

1 2 3 4 For the favoured reaction, the acid and its conjugate base and then the base and its conjugate acid, listed in that order are . (Record all four numbers.)

• II

66. A substance that can act as either an acid or a base is described as A. C.

• I

10

20

30

40

50

60

70

80

90

100

Volume of 0.10 mol/L mol/L NaOH Volume of 0.10 NaOH(aq) (mL) (aq) (mL)

63. The Brønsted–Lowry equation for the reaction which takes place in the region between I and II is H2PO4–(aq) + OH–(aq)  HPO42–(aq) + H2O(l) H3PO4(aq) + OH–(aq)  H2PO4–(aq) + H2O(l) HPO42–(aq) + OH–(aq)  PO43–(aq) + H2O(l) H3PO4(aq) + 2 OH–(aq)  HPO42–(aq) + H2O(l)

64. In order to obtain accurate data to calculate the concentration of the H3PO4(aq) solution, all of the indicators listed below could be used except A. B. C. D.

thymol blue bromothymol blue bromocresol green phenolphthalein ---------------

65. The water in a swimming pool was tested to determine its pH. Phenolphthalein was colourless in a sample of the water and bromothymol blue was blue. The approximate pH of the swimming pool water was A. C.

amorphous isoprotic

B . amphoteric D. allotropic

Numerical Response 0

A. B. C. D.

HCOOH(aq) + SO42–

(aq)

Titration Curve for Titration of 37 mL of 0.10 mol/L H3PO4(aq) with NaOH(aq) 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

HSO4–(aq) + HCOO–(aq)

6.3 8.0

B . 7.0 D. 12.0

12.

A 30.0 mL sample of 0.200 mol/L HCOOH(aq) is titrated with a solution of 0.180 mol/L NaOH(aq). The volume of NaOH(aq) required to react completely with the HCOOH(aq) is __________ mL. (Record your answer to three digits.)

67. When a small amount of base is absorbed into the blood, the H2CO3(aq)/HCO3–(aq) buffer maintains blood pH at approximately 7.3 because the base reacts with A. C.

H2CO3(aq) CO32–(aq)

B . HCO3–(aq) D. H2O(l)

68. Titration of CH3COOH(aq) with NaOH(aq)

71. One of the buffer systems in the human body is HCO3–(aq) + H2O(l)

H2CO3(aq) + OH–(aq).

This buffer system would respond to the addition of vinegar, CH3COOH(aq), by A. replacing the vinegar with OH–(aq) B. reacting the vinegar with carbonic acid C . shifting the equilibrium to the right because [OH–(aq)] would decrease D. shifting the equilibrium to the left, producing more carbonic acid

If the titration is stopped at X, the solution is resistant to a change in pH if a strong base or a strong acid is added to it. This is due to the fact that, at X, the solution contains large amounts of A. B. C. D.

H2O(l) and OH–(aq) CH3COO–(aq) and H3O+(aq) CH3COOH(aq) and OH–(aq) CH3COOH(aq) and CH3COO–(aq)

During respiration, our body’s cells metabolize glucose according to the equation C6H12O6(aq) + 6 O2(aq)  6 H2O(l) + 6 CO2(aq)

69. The metabolism of glucose could, if unbuffered, cause our blood to A. B. C. D.

become more acidic become more basic remain neutral lose energy

70. Hyperventilation (very rapid, deep breathing) results in rapid loss of CO2(g) from our bodies. During hyperventilation, the pH of blood A. B. C. D.

decreases increases remains at normal levels becomes more dilute

72. When citric acid combines with water in the mouth, one reaction that occurs is H3Ct(aq) + H2O(l)

H2Ct–(aq) + H3O+(aq).

The conjugate acid–base pairs in this equation are A. B. C. D.

H3Ct(aq) / H3O+(aq) and H2O(l) / H2Ct–(aq) H3Ct(aq) / HCt2–(aq) and H3O+(aq) / H2O(l) H3Ct(aq) / H2O(l) and H3O+(aq) / H2Ct–(aq) H3Ct(aq) / H2Ct–(aq) and H3O+(aq) / H2O(l)

In Canada, the annual production of ammonia, NH 3(g), exceeds that of any other chemical. About one-quarter of it is used directly as fertilizer. The rest is used as a reactant in the production of explosives and chemicals such as nitric acid.

75. You have been given two unlabelled acidic solutions. One is a weak acid and one is a strong acid, but they have the same pH. Which of the following statements about the two acids is true? A.

One such reaction, 4 NH3(g) + 5 O2(g)

4 NO(g) + 6 H2O(g),

is vital to the Ostwald synthesis of nitric acid.

73. The equilibrium law expression for this reaction is 4

A.

B.

K eq =

K eq =

C.

K eq =

D.

K eq =

6

[NO(g) ] [H2O(g) ]

[NO3(g) ] 4 [O2(g) ] 5

[NO(g) ]4  [H2 O(g) ] 6

HSO3–(aq) HCO3–(aq)

B . HCN(aq) D. HCOOH(aq)

77. A reaction in which equilibrium favours the products is

[NH3(g) ] 4  [O2(g) ] 5 [NO(g) ] [H2O(g) ]

76. Which of the Brønsted–Lowry acids listed below is stronger than H2S(aq)? A. C.

[NH3(g) ]4  [O2(g) ]5

4

The weak acid more easily releases hydrogen ions and is more concentrated than the strong acid. B . The strong acid more easily releases hydrogen ions and is more concentrated than the weak acid. C. The weak acid more easily releases hydrogen ions and is less concentrated than the strong acid. D. The strong acid more easily releases hydrogen ions and is less concentrated than the weak acid.

A. B. C. D.

6

4[NH3(g) ] 6[H2 O(g) ] 4[HN3(g) ] 5[O2(g) ]

HSO4–(aq) + F –(aq) HF(aq) + H2O(l) HF(aq) + SO42–(aq) H3BO3(aq) + F –(aq)

HF(aq) + SO42– (aq) H3O+(aq) + F –(aq) HSO4–(aq) + F –(aq) HF(aq) + H2BO3–(aq)

78. Which of the following substances is amphiprotic? Numerical Response 13.

NH4+(aq) + H2O(l)

H3O+(aq) + NH3(aq)

In a system at equilibrium, the concentration of the NH3(aq) is 0.35 mol/L and the concentration of the NH4Cl(aq) is 0.25 mol/L. The pH of the NH4+(aq) / NH3(aq) solution is __________. (Record your answer to three digits.)

74. The Kb for NH3(aq) is A. C.

10–10

–5.8  1.7  10–5

10–14

B . 1.0  D. 1.7  109

A. B. C. D.

Sodium sulphite Potassium hydrogen sulphite Calcium carbonate Sodium acetate

79. The Cancarb plant in Medicine Hat produces carbon, C(s), from methane gas. To cool the carbon in the production line, it is sprayed with water. In this process, the water becomes increasingly basic. The [OH–(aq)] of the resulting solution is 3.2  10–4 mol/L. The pH of the solution is A. C.

0.50 10.51

B . 3.49 D. 13.50

Use the answer selected from Multiple Choice 79 to answer Multiple Choice 80. 80. Two indicators, used separately, that could be used to confirm the pH of the solution produced at Cancarb are A. B. C. D.

orange IV and bromocresol green methyl violet and cresol red indigo carmine and 1,3,5–trinitrobenzene phenolphthalein and indigo carmine

81. A base is titrated with an acid solution until the indicator changes colour. This change in the colour of the indicator is referred to as the A. B. C. D.

end point equivalence point equilibrium point neutralization point

Numerical Response 14.

The graphs below show the relative concentration of N2O4(g) and NO2(g) as various stresses are exerted on the equilibrium system N2O4(g) + heat 2 NO2(g). (Note: The graphs are not drawn to scale.)

82. The following graph represents the variation over time of the concentrations of O2(g), SO2(g), and SO3(g) for the reaction 2 SO2(g) + O2(g) 2 SO3(g).

Stresses:

1 removing NO2(g) 2 cooling system

3 adding heat 4 adding N2O4(g)

Match each of the graphs with the appropriate stress. Which of the following statements about the graph is true? A. At t = 0, the concentration of SO2(g) is 30 mmol/L. B . At equilibrium, the concentration of SO2(g) is 30 mmol/L. C. At equilibrium, the concentration of SO3(g) is 60 mmol/L. D. At equilibrium, the concentration of SO3(g) is about half that of SO2(g).

Graph M __________ Graph N __________ Graph O __________ Graph P __________

(Record in column 1) (Record in column 2) (Record in column 3) (Record in column 4)

Anthocyanins (represented as A+(aq)) are responsible for the red colour of wine. Anthocyanins can react with water as follows 2 H2O(l) + A+(aq)

H3O+(aq) + AOH(aq).

Cancarb Ltd., a company located in Medicine Hat, produces high-quality carbon through the thermal decomposition of natural gas. The natural gas is heated in the absence of oxygen to 1300°C in a reaction chamber. The reaction is represented by the equation

The AOH(aq) form is colourless. In a particular white wine sample, the equilibrium [H3O+(aq)] is 8.5  10–4 mol/L.

Numerical Response 15.

The pH of the white wine at equilibrium is __________ (Record your answer to three digits .)

CH4(g)

85. The thermal decomposition process extracts only about 50% of the carbon from the natural gas. Some of the remaining carbon reacts to form carbon dioxide when it is released into the atmosphere. Which of the following statements relating to carbon dioxide is false? A. B.

Use the answer selected from Numerical Response 15 to answer Multiple Choice 83. 83. A few drops of methyl orange indicator were added to the white wine sample. The resulting solution would be A. C.

colourless orange

C. D.

B . yellow D. red

A. C.

2.24  9.38  10–4

B . 1.07  D. 4.46  10–4 101

Carbon dioxide reacts with moisture in the air to produce carbonic acid. Carbon dioxide absorbs infrared radiation and radiates the energy back toward Earth. Carbon dioxide attacks the ozone layer. Carbon dioxide increases with deforestation.

86. The conditions that should maximize the amount of product formed are A. B. C. D.

84. If the initial concentration of anthocyanins, prior to equilibrium, was 1.62  10–3 mol/L, the Ka for anthocyanins is 103

C(s) + 2 H2(g)

low pressure and low temperature low pressure and high temperature high pressure and low temperature high pressure and high temperature

87. When a sample of the high-quality carbon is soaked in distilled water, the resulting solution has a pH of approximately 10.0. This pH is probably caused by an impurity such as A. C.

K2SO4(aq) Al(NO3)3(aq)

B. D.

BaCl2(aq) Na2CO3(aq)

Numerical Response 16.

A solution prepared by mixing a sample of carbon with NaCl(aq) has a pH of 9.93. The pOH of this solution is __________. (Record your answer to three digits.)

88. The purity of high-quality carbon can be determined by soaking a sample in water and then measuring its pH. “Ultrapure” grade has a pH of 6.00, and “Thermax” grade has a pH of 10.00. The [OH–(aq)] of these two grades of high-quality carbon are, respectively, A. B. C. D.

Use the following additional information to answer the next two questions. Titration of a Halide Acid with 1.0 mol/L NaOH(aq)

1.0  10–6 mol/L and 1.0  10–10 mol/L 1.0  10–8 mol/L and 1.0  10–4 mol/L 4.0 mol/L and 8.0 mol/L 8.0 mol/L and 4.0 mol/L

89. Red cabbage boiled in a dilute, household cleaning solution produces a bright green solution. When a person blows into the solution through a straw, the solution turns blue. The cabbage solution is an example of A. C.

an acid a reducing agent

B. D.

an oxidizing agent an indicator

90. A conjugate acid–base pair is A. B. C. D.

93. The halide acid that would generate the data on the graph is

CH3COOH(aq) and CO32–(aq) HCO3–(aq) and CO32–(aq) H2S(aq) and H2PO4–(aq) OH–(aq) and CO32–(aq)

A. C.

91. A 10.0 mL sample of CH3COOH(aq) is titrated to the equivalence point with 35.0 mL of 0.0714 mol/L NaOH(aq).

HF(aq) HI(aq)

B. D.

HCl(aq) HBr(aq)

94. The indicator that would best signal the endpoint of this titration is A. C.

methyl orange B. phenolphthalein indigo carmine D. bromothymol blue ---------------

The concentration of the CH3COOH(aq) is A. C.

2.04 mol/L 0.125 mol/L

B. D.

0.250 mol/L 0.0200 mol/L

Use the following information to answer the next three questions. Hydrogen Halides

H–X Bond Energy (kJ/mol)

Melting Point (°C)

HF HCl HI HBr

565 427 363 295

–83 –114 –87 –51

H°f (kJ/mol)

–271.1 –92.3 +26.5 –36.4

Ka

6.6  10–4 1.3  106 3.2  109 1.0  109

92. The hydrogen halides, ordered from the strongest acid to weakest acid, are A. C.

HI, HBr, HCl, HF HBr, HCl, HI, HF

B. D.

HBr, HI, HCl, HF HF, HI, HCl, HBr

Combustion of unscrubbed fossil fuels releases sulphur oxides into the air. These sulphur oxides eventually form H2SO3(aq) and H2SO4(aq) when combined with water vapour. The presence of these and other components of acid rain cause the pH of “normal” rain to decrease from about 6.00 to a recorded low of 2.30 in some areas.

95. One property of acid rain is that it A. B. C. D.

turns red litmus blue tastes bitter reacts with active metals feels slippery

96. Indicators are added to three samples of acid rain from the same source. The samples with methyl orange and chlorophenol red are yellow. The sample with methyl red is red. The approximate pH of the acid rain samples is A. C.

3.0 5.0

B. D.

4.6 5.5

97. The pH of a lake affected by acid rain could be adjusted to “normal” levels through the addition of A. C.

CH3OH(l) NaCl(s)

B. D.

HCl(aq) CaCO3(s)

98. In a highly industrialized area, the rain has an average pH of 4.5, but the pH of the soil has not changed enough to affect plant growth. The best explanation is that the A. B. C. D.

Use the following additional information to answer the next two questions. Titration of Sulphurous Acid with Potassium Permanganate Volume of sulphurous acid samples = 100.0 mL Concentration of KMnO4(aq) = 0.0310 mol/L Volume of KMnO4(aq) Trial

1

Final buret reading (mL) 9.50 Initial buret reading (mL) 1.00 Final colour of mixture pink

2

3

4

18.15 26.75 34.75 9.50 18.15 26.75 pink pink colourless

Numerical Response 17.

soil has a good buffering capacity acid is not completely dissociated plants are resistant to an increase in pH soil has a high concentration of hydronium ions

To determine the concentration of the sulphurous acid, the average volume of potassium permanganate used is __________ mL. (Record your answer to three digits.)

Use the value selected for Numerical Response 9 to answer Numerical Response 10. 99. The Brønsted–Lowry equation for the dissociation of sulphurous acid in aqueous solution is A. B. C. D.

H2SO3(aq) + H2O(l) SO42–(aq) + 2 H+(aq) + – 2e H2SO3(aq) + 2 H2O(l) SO32–(aq) + 2 H3O+(aq) H2SO3(aq) + H2O(l) HSO3–(aq) + H3O+(aq) H2SO3(aq) SO42–(aq) + 2 H+(aq)

Numerical Response 18.

The concentration of sulphurous acid in the sample is __________ mmol/L. (Record your answer to three digits.) ---------------

101.

pH Curve

Use the following information to answer the next three questions. A student titrated samples of sulphurous acid with a potassium permanganate solution. 100. The balanced net ionic equation for the titration is A. B. C. D.

2 MnO4–(aq) + 5 H2SO3(aq) + 6 H+(aq)  2 Mn2+(aq) + 5 SO42–(aq) + 3 H2O(l) – 2 MnO4 (aq) + 5 H2SO3(aq)  2 Mn2+(aq) + 5 SO42–(aq) + 4 H+(aq) + 3 H2O(l) 2 MnO4–(aq) + 5 H2SO3(aq) + 16 H+(aq)  2 Mn2+(aq) + 5 SO42–(aq) + 20 H+(aq) + 3 H2O(l) 2 MnO4–(aq) + 5 SO42–(aq) + 36 H+(aq)  2 Mn2+(aq) + 5 H2SO3(aq) + 13 H2O(l)

The graph represents the titration of A. B. C. D.

sodium hydroxide with hydrochloric acid potassium hydroxide with oxalic acid hydrochloric acid with ammonia acetic acid with sodium hydroxide

Numerical Response 19.

When 0.10 mol of NH4NO3(s) is dissolved in water to produce 1.0 L of solution, the pH of the solution is __________. (Record your answer to three digits.)

Tooth decay results from the dissolving of tooth enamel, Ca5(PO4)3OH(s). This decay is represented by the equilibrium equation Ca5(PO4)3OH(s)

5 Ca2+(aq) + 3 PO43–(aq) + OH–(aq)

102. An acid that is not polyprotic is A. C.

HOOCCOOH(aq) HCOOH(aq)

B. D.

H2BO3–(aq) H2SO4(aq)

103. In all chemical systems at equilibrium, A. B. C. D.

macroscopic properties are changing all the reactants are converted to products the amount of reactants equals the amount of products the forward reaction rate equals the reverse reaction rate

104. For the steam–hydrocarbon reforming process, the equilibrium law expression is:

K eq 

[CO2(g ) ][H2(g ) ] 4

CH4(g) CO2(g) CH4(g) CO2(g)

+ + + +

A. B. C. D.

is formed as the concentration of the phosphate ion decreases and the equilibrium shifts to the left is formed as the concentration of the hydroxide ion decreases and the equilibrium shifts to the left dissolves as the concentration of the hydroxide ion decreases and the equilibrium shifts to the right dissolves as the concentration of calcium ion decreases and the equilibrium shifts to the right

106. If the equilibrium constant, Keq , for the dissolving of tooth enamel has a value of 2.07  10–30, then the Keq value for the reverse reaction is A. C.

4.83  1029 2.07  10–16

B. D.

4.83  1015 –2.07  10–30

[CH4(g) ][H 2O(g ) ] 2

The reaction described by this equilibrium is A. B. C. D.

105. When sugar ferments on teeth, the pH level inside the mouth decreases. Tooth enamel

2 H2O(g) CO2(g) + 4 H2(g) 4 H2(g) CH4(g) + 2 H2O(g) H2O(g) CO2(g) + H2(g) H2(g) CH4(g) + H2O(g)

107. Most toothpastes contain fluoride compounds that mineralize tooth enamel forming Ca 5(PO4)3F(s). The Ca5(PO4)3F(s) is more resistant to decay in an acidic medium than Ca5(PO4)3OH(s) because fluoride is a A. B. C. D.

stronger base than hydroxide ion and is more likely to react weaker base than hydroxide ion and is more likely to react weaker base than hydroxide ion and is less likely to react stronger base than hydroxide ion and is less likely to react

WRITTEN RESPONSE - 12 marks

1.

The Haber-Bosch process for the industrial production of ammonia involves the equilibrium N2(g) + 3H2(g)

WRITTEN RESPONSE - 12 marks 3.

2NH3(g) + 92.2 kJ

In a laboratory experiment designed to study this equilibrium, a chemical engineer injects 0.20 mol of N2(g) and 0.60 mol of H2(g) into a 1.0 L flask at 500°C. She records her analysis of the contents of the flask at 5 s intervals in the table shown. Time(s) 0 5 10 15 20 25

N2(g) 0.20 0.14 0.11 0.10 0.10 0.10

Concentration H2(g) 0.60 0.42 0.33 0.30 0.30 0.30

Describe a procedure that would allow you to determine if an unidentified 0.100 mol/L acid is monoprotic or polyprotic. You have available standard laboratory equipment and a range of reagents. Describe the relevant results that would help you decide whether the sample is monoprotic or polyprotic.

WRITTEN RESPONSE - 12 marks NH3(g) 0.00 0.12 0.18 0.20 0.20 0.20

4.

Analyze the data. Your responses should include • a plot of the concentrations of N2(g), H2(g), and NH3(g) versus time on the grid provided, including an appropriate title • the time required to establish equilibrium • the equilibrium constant for the reaction • two methods, other than increasing the amounts of reactants, that could increase the yield of ammonia

A crayon manufacture is now making markers that change colour when a colourless Changeable™ marker overwrites the coloured Changeable™ marker. Suggest a possible composition for each of the markers used to produce the graphic shown above. Your response should indicate reagents and reactions involved and should take into account that the markers are intended for use by young children.

WRITTEN RESPONSE - 12 marks 2.

When corrosive materials such as concentrated hydrochloric acid are shipped in tanker trucks, there is always the potential for accidental leakage. What steps should be taken to neutralize an accidental spill of hydrochloric acid in a roadside ditch? Explain the rationale behind your strategy. Your response should include appropriate chemical equations.

June 1998

101. A 105. C

WRITTEN RESPONSE - 12 marks The unique flavour of fruits and berries is due to the presence of esters, chemical compounds that are easily synthesized in the laboratory. For example, ethyl propanoate is responsible for the flavour characteristic to pineapple. It is produced by the reaction

5.

102. C 106. A

103. D 107. C

104. A

NUMERICAL RESPONSE ANSWERS 1. 13.3 3. 2.84

2. 1 3 2 4 4. 2 4 3 1

C2H5OH(l) + C2H5COOH(l) C2H5COOC2H5(l) + H2O(l)

5. 1 2 4 5 7. 7.32

6. 1 2 4 3

When 7.71 mol of C2H5OH(l) and 7.37 mol of C2H5COOH(l) are reacted in a beaker, 4.80 mol of C2H5COOC2H5(l) are present when equilibrium is established and the total volume of liquid is exactly 1.00 L.

8. 0.40

Calculate Keq for this system. Are the reactants or products favoured at equilibrium? Justify your choice.

9. 2.00 11. 1 4 2 3

10. 1.33 12. 33.3

13. 9.38 15. 3.07

14. 3 1 4 2

16. 4.07 18. 6.65

17. 8.58 19. 5.12

WRITTEN RESPONSE ANSWERS

Concentration (mol/L)

1.

ACID-BASE MULTIPLE CHOICE ANSWERS 1. 5. 9. 13.

B D C C

2. 6. 10. 14.

A C A D

3. 7. 11. 15.

D D C A

4. A 8. D 12. B

16. 17. 21. 25. 29.

C B C D C

18. 22. 26. 30.

C C B A

19. 23. 27. 31.

B B A C

20. B 24. D 28. D

32. 36. 40. 44. 48.

B C A B C

33. 37. 41. 45. 49.

D A B A B

34. 38. 42. 46. 50.

D A D B C

35. 39. 43. 47. 51.

C B D D D

52. 56. 60. 64. 68.

B C C B D

53. 57. 61. 65.

B D D C

54. 58. 62. 66.

D B A B

55. 59. 63. 67.

A B A A

69. 73. 77. 81.

A A A A

70. 74. 78. 82.

B C B B

71. 75. 79. 83.

C D C D

72. 76. 80. 84.

D D D C

June 98 85. C 89. D 93. A 97. D

86. 90. 94. 98.

B B B A

87. 91. 95. 99.

D B C C

88. 92. 96. 100.

B A B B

0.6 0.5 0.4 0.3 0.2 0.1 0 0

5

10 Time (s)

15

nitrogen hy drogen ammonia •

The time required to establish equilibrium is 15 s. (depends on graph) [NH3 ] 2 (0.20)2 • Keq = = = 15 3 [N2 ] [H2 ] (0.10)(0.30)3 • Remove ammonia as it is formed. • Increase the concentration of the reagents by decreasing volume. • Decrease the temperature

20

25

2.

Note: Acceptable responses will vary greatly. The hydrochloric acid could be neutralized on site by the addition of a base such as calcium carbonate (limestone). The addition of limestone is a good choice because excess limestone would not affect the environment thus an excess can be added and you need not worry about the exact amount required. 2 HCl(aq) + CaCO3(s)  CaCl2(aq) + 2 H2O(l) + CO2(g) The on-site neutralization reduces the shipping and clean up problems since the hydrochloric acid does not need to be gathered up, picked up, and transported away.

3.

Procedure: a. Pipet a specific volume of the acid solution into a beaker. b. Place the electrode of a pH meter in the acid solution. c. Titrate the acid sample with a known concentration of a strong monoprotic base, such as NaOH(aq), until a pH of 13 is reached. d. Record the pH after each small addition of base. Analysis: Plot the recorded data on a graph of pH vs. volume of titrant. •If the pH curve has one step, the acid is monoprotic. •If the pH curve has more than one step, the acid is polyprotic.

4.

One possible mechanism for this marker is to use methyl red indicator as the dye in the coloured marker. At a pH of 5 the marker colour would be red, thus the marker would not be strongly acidic and hence relatively safe. The colourless over writer could be a dilute solution of sodium hydroxide. The pH of which could be around 8, thus it would be relatively safe yet basic enough to change the indicator from its red form to the yellow form. The reaction for the color change is HMr(aq) + OH-(aq)  Mr-(aq) + HOH(l) red yellow