Unit 5- Solutions, Acids, and Bases

Terms to Know Solvent= liquid that dissolves the chemical compound (usually water) Solute= substance that dissolves into the water

Dissolution= process of dissolving Aqueous (aq) = water based solutions ex: NaCl(aq) = salt water Soluble- ability of a solvent to dissolve a solute.

solute + solvent = solution

Ex: Solute & Solvent • Your blood is a solution: • Solvent= plasma (which is mostly water) • Solute= white blood cells, red blood cells, etc.

Why Water is a Great Solvent • Water is POLAR!! – It is unevenly charged – The highly electronegative oxygen hogs the electrons.

• Polar & ionic solutes will dissolve in water because of the charges.

“Like Dissolves Like” Rule of Thumb for Solubility: • Charged things dissolve in charged things : – Polar/ Ionic solutes will dissolve in polar solvents.

• Nonpolar solutes will dissolve in nonpolar solvents.

“Like Dissolves Like” Polar/Ionic compounds dissolve in polar solvents.

Sugar (polar) mixes with water (polar) for easy cleaning.

Non polar compounds dissolve in non polar solvents.

Grease, oil and gasoline (non polar) will dissolve one another.

Not all solutes are water soluble • Nonpolar substances do NOT dissolve in water – Ex: Oil & Water

• Nonpolar substances will only dissolve in nonpolar solvents!

Substances that are soluble in H2O: “Like Dissolves Like”

Ionic Compounds (ex: salts) – made up of + cations and anions. – charged ions attracted to the polar ends of water

Polar Substances (ex: Sugar) – Covalently bonded – Both sugar and water are polar.

Dissolving of Ionic Substancesex: NaCl (salt) •charged (Na+ & Cl-) are more attracted to several polar water molecules and are pulled apart.

•They dissociate (break apart)

Dissolving of Polar Substancesex: C6H12O6 (Glucose) • Polar water surrounds the glucose molecules and pulls them away from each other

Weak hydrogen bond between glucose is broken and glucose is surrounded by water

• Molecules themselves remain intact

FYI-Why does soap dissolve both polar & nonpolar things? -Alcohol, soap, & acetone will dissolve most substances because contain polar and non-polar regions.

How soap can dissolve a lot of substances

FYI-Cell Membranes- have both polar & nonpolar ends

Properties of Solutions & The Dissolving Process

Electrolytes • Electrolyte= a substance containing free ions (charged particles) that will conduct electricity. • acids, bases or salts All these substances disassociate/ break apart in water: NaCl Na+ + Cl- (in water)

HCl H+ + Cl – (in water) NaOH Na + + OH – (in water)

Non Electrolytes • Some solutions do not conduct electricity. They are called nonelectrolytes. Examples include: sugar ethanol (alcohol) ethylene glycol

FYI:Sports Drinks & Electrolytes • Electrolytes are important in your body because they are what your cells use to carry electrical impulses (nerve impulses, muscle contractions) across themselves and to other cells.

• As for your body, the major electrolytes are as follows: – – – – – – – –

sodium (Na+) potassium (K+) chloride (Cl-) calcium (Ca2+) magnesium (Mg2+) bicarbonate (HCO3-) phosphate (PO42-) sulfate (SO42-)

• When you exercise, you lose electrolytes through your sweat. • Many sports drinks now contain electrolytes to replenish what you have lost.

Source: Howstuffworks "What are electrolytes?“. Created 3/19/2008. HowStuffWorks.com. 3/19/2008. http://health.howstuffworks.com/question565.htm

FYI: Tasers- you conduct electricity

Factors that Speed up Dissolving Process -Need to make the solute & solvent come into contact more frequently

1) Increase Temperature-

makes molecules move faster

2) Increase Surface areamore surfaces to interact with

3) Stirring/ Shaking

4) Increasing Pressureonly works for gases

Solubility Curves-

Show much solvent you can put in H2O @ certain Temp. • Solubility usually increases as temperature increases • EX: • At 20°C, 200 g of sugar will dissolve in 100g (= 100 mL) of H2O. • If the temp. is increased to 60°C, 300g of the sugar will dissolve in 100g (or 100mL) H2O.

Solubility Practice Problems What mass of solute will dissolve in 100mL of water at the following temperatures. : Answers: 1 .

KNO3at 70°C

140g / 100mL

2 .

NaCl at 100°C

40g / 100mL

3 .

NH4Cl at 90°C

72g / 100mL

.

Concentration of a Solution • Amount of solute is dissolved in a given amount of solution. • Unsaturated Solution (dilute)– more solute can be dissolved • Saturated Solution (full)– no more solute can be dissolved under @ that temp • Saturation Point • Supersaturated Solution– the solution has a higher solute concentration than can be reached under normal conditions.

Supersaturated solution

Saturated solution

Unsaturated solution

Crystallization occurring when solution cools

Calculating Concentrations in Solutions

Concentration=

Amount of solute (part) Amount of solvent (whole)

Can be expressed in: – %composition – Parts per million (ppm) – Grams/ Liter 10 Fish

2 Fish

1L

1L

– Molarity (M)

Conversion factors to know: 1 g H2O = 1 mL

1 L = 1000 mL

% Composition grams of solute grams of solution

X 100

• 1 mL water = 1 gram of water – These solutions are so dilute, we can assume that 1 mL solution = 1 gram of solution Example 1: 13.0 grams of NaOH is dissolved in enough water to make 850 mL of solution. – Given: 13.0 g NaOH 850 mL solution = 850 g solution – Find: percent composition 13.0 g NaOH 850 g solution

X 100 = 1.53 % NaOH

Back of Toothpaste

Parts per million (ppm)-

Used to describe the concentration of very dilute solutions

grams of solute grams of solution

X 106

Example 1: 13.0 grams of NaOH is dissolved in enough water to make 850 mL of solution. • Given: -13.0 g NaOH (solute) –850 mL solution = 850 g* (solution) *(1 mL water = 1 gram of water… so dilute we can assume this 1 mL = 1 gram)*

• Find: ppm 13.0 g NaOH 850 g solution

X 1,000,000 = 15294 ppm NaOH

What’s in your drinking water? National Primary Drinking Water Standards as of 10/03 Contaminant

Parts per Million (ppm)

Potential Health Effects from Ingestion of Water

Arsenic

0.010

Skin damage or problems with circulatory systems, and may have increased risk of getting cancer

Asbestos (fibers >10

7 (million

Increased risk of developing benign intestinal polyps

micrometers)

fibers per Liter)

Carbon tetrachloride

0.005

Liver problems; increased risk of cancer

Lead

0.015

Infants and children: Delays in physical or mental development; children could show slight deficits in attention span and learning abilities; Adults: Kidney problems; high blood pressure

Mercury (inorganic)

0.002

Kidney damage

Source: US EPA. Water On Tap: What You Need To Know. Modified 12/14/2004. EPA. 3/13/2008. http://www.epa.gov/safewater/wot/pdfs/book_waterontap_full.pdf

Grams per liter grams of solute Liters of solution • Used to discuss the solubility of a solid in solution. • Example: 13.0 grams of NaOH is dissolved in enough water to make 850 mL of solution. – Given: 13.0 g NaOH 850 mL solution = 0.850 L solution – Find: g/L – Solve:

13.0 g NaOH 0.850 L

= 15.3 g/L

Expressing Concentrations of Solutions

Molarity (M) =

moles solute liters of solution

PROBLEM: What is the molarity of a solution prepared by dissolving 24.5 g of NaCN in water to a final volume of 250.O mL? Step 1: Molarity = moles Liters Step 2: Convert grams to Moles 24.5 g NaCN x

1 mole NaCN = 0.500 mol 49.01 g

Step 3: Convert mL to L 250.0 mL x

1 L

= .2500 L

1000mL Step 4: Plug into equation M = 0.500 mol 0 .2500

= 2.00 M NaCN

Ex #1 (no calculator needed) How many moles of HNO3 are needed to prepare 5.0L of 2.0 M solution of HNO3? Solution: Molarity= moles Liter

2.0 M

= moles 5.0 L

= 10 moles

Labeling on solutions in chemistry

Kool- Aid Lab- a little history

Over 900 people died in a “mass suicide” by drinking punch laced with poisons

Chemistry of Acids and Bases

pH Scale- a way of expressing the strength of acids and bases

Common Acids HC2H3O2

Acetic Acid

Vinegar

HCl

Hydrochloric Acid

Stomach acid

H3C6H5O7

Citric Acid

Citrus Fruit

HNO3

Nitric Acid

H2SO4

Sulfuric Acid

Battery Acid

Some Common Bases NaOH

sodium hydroxide

lye/ Drano

KOH

potassium hydroxide

liquid soap

Ba(OH)2

barium hydroxide

stabilizer for plastics

Mg(OH)2

magnesium hydroxide

Milk of magnesia

Al(OH)3

aluminum hydroxide

Maalox (antacid)

NH3

Ammonia

Windex & cleaners

What Are Acids & Bases? (Arrhenius theory)

• Acids - Increase the concentration of hydrogen ions (H+) in aqueous solution. – Examples: HCl, H2SO4, HNO3

• Bases - Increase the concentration of hydroxide ions (OH-) in aqueous solution. – Examples: NaOH, Mg(OH)2, KOH,

Characteristic Ions of Acids Hydrogen Ion (H+)

Hydronium Ion (H3O+)

• Many acids contain H+ • Acids dissociate in H2O, # of H+ ions increases in the solution

Acid donates H2O

to

HCl +

H2O

• As H+ interact with water molecules, they combine to form H3O+

H3O+ = hydronium ion



H 3O + gives solution the acidic properties

+

Cl-

Hydronium Ion (detailed FYI) H2O with extra proton (H+) H & Cl form a polar covalent bond, but H is very attracted to water.

Some Properties of Acids • • • • • • •

Produce H+ ions (+ H2O)  H3O+, hydronium ion

0-7 on pH scale Taste sour Acids are Electrolytes Acids are neutralized with a base (forms salt + water) Turns blue litmus paper to “Red”

Reacts with metals to form H2 gas

HCl +

Mg

 MgCl2 + H2 gas

(Acid) + (metal)

Why we use Drano (a base) in our drain pipes vs. acids

Capsaicin- Acid found in chilis • All sorts of interesting applications: – Pain relief for topical application on arthritic limbs – Animal deterrent – Drug abuse deterrent – Diet function Pepper spray

Characteristic Ion of Bases • Hydroxide Ion (OH-) • Many bases contain OH• As bases dissociate in water, the concentration of OH- ions increases in the solution

2 ways to explain Bases: 1) Donators of OH- ions water NaOH  Na+ (aq) + OH- (aq)

2) Acceptor of H+ ions

Some Properties of Bases  Produce OH- ions in water (hydroxide) / Accept H+ ions  pH greater than 7-14  Taste bitter, chalky  Are electrolytes  Feel soapy, slippery

 Are neutralized by acids (form salt + water)  Turns red litmus paper to blue “Basic Blue”

Strong vs. Weak Acids & Bases • Strength of an acid or base is determined by the amount of ionization (how often it dissociates in water) • Examples: – Strong acid: hydrochloric acid (HCl) – Weak acid: Acetic acid (vinegar) – Strong Base: sodium hydroxide (NaOH) – Weak Base: Ammonia (NH3)

Strong- break apart easily

Weak – Do NOT ionize as much

Ex: Strong vs. Weak Acids/Bases HCl= strong acid that completely breaks apart in water.

Acetic Acid= weak acid that does not completely break apart in water

Strong acids/ bases = strong electrolytes • Strong acids (dissociate 100% in water)= HNO3, HCl, H2SO4 and HClO4 • Weak acid = acetic acid (aka vinegar) CH3CO2H • Strong base (dissociate 100% in water) = NaOH (aq) ---> Na+ (aq) + OH- (aq) • Weak base = Ammonia (NH3) NH3 (aq) + H2O (l)  NH4+ (aq) + OH- (aq)

pH Scale- a way of expressing the strength of acids and bases

pH & the Environment

pH testing- Lots of ways! Some chemicals respond to acids &/or bases by changing colors

pH- paper

pH meter

Phenolphthalein (PPT) responds to bases only

pH indicator: Cabbage Juice By boiling purple cabbage, the natural pigments can serve as an indicator.

Some other pH chemical indicators Some indicators work only in a specific pH range.

Neutralization Reactions

Neutralization- a special type of double replacement reaction

Tums neutralizes the acid in your stomach.

Neutralization Reactions Cont. • Acids React with Carbonates You may have made a volcano : 2HC2H3O2 + Na2CO3 2 NaC2H3O2 + H2O + CO2 Vinegar + Baking Soda  Sodium acetate (salt)

Effects of Acid rain on marble H2SO4 + CaCO3  CaSO4 + H2O + CO2

Titration- way of determining the molarity of an unknown solution. drop base of known Molarity into acid until it’s neutralized acid of unknown strength W/ indicator in it By knowing how much base it took to neutralize acid (& a little math) you can find the strength. Formula: MV = MV (see problem on next slide)

Titration Problem:35 mL of NaOH is neutralized with 25 mL of 0.1 M HCl by titration to an equivalence point. What is the concentration of the NaOH? Use formula: (Molarity acid) (*Volume acid) = (Molarity base) (*Volume base) *Volume must be in Liters (1 L = 1000 mL)*

Solution: Plug & Chug …(0.1 M ) (0.025 L) = (?M) (0.035 L) M= 0.07 M NaOH

Buffers