Name_______________________ Chem 305
Partner_______________________ Section (Circle) M Tu W Th F
Date_______________________
WORKSHOP: Matter and Working with Significant Figures Part 1: Classifying Matter: Circle the appropriate words to make the statements true. 1. A mixture (is/is not) a chemical combining of substances. 2. In a compound the (atoms/molecules) are (chemically/physically) combined so that the elements that make up the compound (retain/lose) their identities and (do/do not) take on a new set of properties. 3. The smallest identifiable unit of a compound is a(n) ______________ , which is made up of _______________which are chemically bonded. 4. (True or False): A mixture is always made up of a combination of elements. 5. In a mixture, the substances (lose/retain) their identities. 6. In a mixture the substances involved (can/cannot) be separated by a simple physical process. In a compound the elements involved (can/cannot) be separated by a simple physical process because the elements are (physically combined/chemically bonded). 7. (True or False): An element can be broken down into a simpler substance. 8. The smallest identifiable unit of an element is a(n) _______________ . 9. From the following list of substances, circle the ones that are elements: silver carbon dioxide air chromium water
hydrogen
carbon
nitrogen
oxygen
gold
sugar
salt
10. How would you separate sand and water in a mixture?
12. Explain how to separate the sugar and water in a solution of sugar and water. Work Check
2-1 Adapted from Lalibert, 7/17/08
Name_______________________
13. Classify the following as pure substances (pure) or as mixtures (mix): air: _____________
gasoline: ______________
orange juice: ________
tap water: _________
sugar: _____________
gold: _________________
mercury: ___________
oxygen: _______________
salt water: __________
14.Classify the following as heterogeneous (het) or as homogeneous (hom): sand & salt mix: ______
hydrogen: ___________
iron: _________________
salt water: _________
filtered air: _________
iron with rust: ______
wood: ____________
an apple: ____________
tossed salad: _________
15.Classify the following as an element, a compound, a homogeneous mixture, or a heterogeneous mixture: aluminum: _________________ raisin bread: __________________________ carbon dioxide: _____________ pure water: ________________________ sugar and water: ____________ sodium chloride: ____________________ an orange: _________________ water & instant coffee: ___________________ hydrogen: _________________ carbon particles & sugar: _______________ gasoline: __________________ neon: ________________________ Work Check
2-2 Adapted from Lalibert, 7/17/08
Name_______________________
Elements, Compounds, and Mixtures Classify each of the pictures below by placing the correct label in the blanks below: A= Element D= Mixture of compounds B= Compound E= Mixture of elements and compounds C= Mixture of elements Each circle represents an atom and each different color represents a different kind of atom. If two atoms are touching then they are bonded together.
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)
12)
13)
14)
15)
2-3
Work Check
Name_______________________
Part 2: Physical and Chemical Changes to Matter Place a check in the appropriate column: Change
Physical Chemical Change Change
Salt dissolves in water. Hydrochloric acid reacts with magnesium to produce hydrogen gas. A piece of copper is cut in half. A sugar cube is ground up. Water is heated and changed to steam. Iron rusts. Ethyl alcohol evaporates. Ice melts. Milk sours (goes bad). Sugar dissolves in water. Sodium and potassium react violently with water. An antacid relieves heartburn. Grass grows on a lawn. A tire is inflated with air. Oxygen and hydrogen combine to form water. Water is absorbed by a paper towel. Ethyl alcohol boils at 79°C. Paper burns. Work Check
2-4
Name_______________________
Part 3 Mixed Practice INSTRUCTIONS: Write het in the blank if the material is heterogeneous or hom if it is homogeneous. 1. face cream
5. dirt
2. filtered green tea
6. sausage pizza
3. gravel
7. laundry bleach
4. Lucky Charms®
8. store-bought milk
INSTRUCTIONS: Classify each of the following as an element [E], a compound [C], or a mixture [M]. 9. calcium
13. pancake syrup
10. nitrous oxide
14. carbon monoxide
11. seawater
15. silver
12. sugar
16. ice
INSTRUCTIONS: Classify each of the following properties of matter as physical [P] or chemical [C]. 17. Color
21. Reacts violently with chlorine
18. Density
22. Good conductor of heat
19. Burns easily (flammable)
23. Dissolves readily in water
20. Not affected by acids
24. Melts at 145 °C
INSTRUCTIONS: Classify each of the following changes in matter as physical [P] or chemical [C]. 25. Grinding chalk into powder
29. Burning gasoline
26. Dissolving salt in water
30. Hammering gold into foil
27. Dissolving zinc in acid
31. Melting ice
28. Stretching copper into wire
32. Making hydrogen from water Work Check
2-5
Name_______________________
Part 4: Significant Figures, Scientific Notation, & Rounding How can we determine how many significant numbers a measurement has? The following rules apply to determining the number of significant figures in a measured quantity: 1. All NONZERO digits ARE significant: 457 cm (three significant figures) 0.25 g (two significant figures). 2. IMBEDDED ZEROS (between nonzero digits) ARE significant 1005 kg (four significant figures) 1.03 cm (three significant figures). 3. LEADING ZEROS (to the left of the first nonzero digits in a number) ARE NOT significant; they merely indicate the position of the decimal point: 0.02 g (one significant figure) 0.0026 cm (two significant figures). 4. ENDING ZEROS that are to the right of the decimal point ARE significant 0.0200 g (three significant figures) 3.0 cm (two significant figures). 5. ENDING ZEROS that are not to the right of a decimal point MAY BE significant: 130 cm (two or three significant figures) 10,300 g (three, four, or five significant figures). The way to remove this ambiguity is described on the following page. Use of standard exponential notation avoids the potential ambiguity of whether the zeros at the end of a number are significant (rule 5). For example, a mass of 10,300 g can be written in exponential notation showing three, four, or five significant figures: 1.03 x 104 g 1.030 x 104 g 1.0300 x 104 g
(three significant figures) (four significant figures) (five significant figures)
In these numbers all the zeros to the right of the decimal point are significant (rules 2 and 4). 1. Determine the number of significant figures in each of the following measured values: a) 200,073
_____
b) 0.00084
_____
c) 5.001
_____
d) 0.0620
_____
e) 107.010
_____
f)
_____
g) 3.400 x 103
_____
h) 3.40 x 103 2-6
3400
_____
Name_______________________ Rounding
When we express a value to the correct number of significant figures, this often requires rounding. To round off decimals: ♦ Find the place value you want (the "rounding digit") and look at the digit just to the right of it. ♦ If that digit is less than 5, do not change the rounding digit but drop all digits to the right of it. ♦ If that digit is greater than or equal to five, add one to the rounding digit and drop all digits to the right of it.
To round off whole numbers: ♦ Find the place value you want (the "rounding digit") and look to the digit just to the right of it. ♦ If that digit is less than 5, do not change the "rounding digit" but change all digits to the right of the "rounding digit" to zero. ♦ If that digit is greater than or equal to 5, add one to the rounding digit and change all digits to the right of the rounding digit to zero. NOTE: It may be necessary to use scientific notation to correctly
2. Round the value 673.1482 to:
3. Round the value 50.0696 to:
5 sig figs _______________
4 sig figs _______________
3 sig figs _______________
3 sig figs
_______________
2 sig figs _______________
2 sig figs 1 sig fig
_______________ _______________
1 sig fig
_______________
4. Round the value 273.84 to:
5. Round the value 48372000 to:
4 sig figs _______________
4 sig figs _______________
3 sig figs _______________
3 sig figs _______________
2 sig figs _______________
2 sig figs _______________
1 sig fig
1 sig fig
_______________
_______________
Work Check
2-7
Name_______________________
Scientific Notation In scientific notation, all numbers are represented by number with one non-zero digit to the left of the decimal place multiplied by ten raised to the appropriate power. • •
Small number (less than 1) will have negative exponents of 10. Large numbers (greater than 1) will have positive exponents of 10.
WORKING WITH SIGNIFICANT FIGURES Addition and Subtraction When adding or subtracting, the number of digits to the right of the decimal point in the answer equals the measurement which has the least number of digits to the right of the decimal point. EXAMPLE: adding:
EXAMPLE: subtracting:
26.46 this has the least digits to the right of the decimal point (2) + 4.123 30.583 rounds off to* → 30.58 ↑ 2 digits to the right of the decimal point 26.46 - 4.123 22.337 rounds off to → 22.34
Perform the following additions or subtractions. Report your results to the proper number of significant figures.
a) 28 + 16 + 227 =
__________
b) 2.222 + 2.22 + 2.2 =
__________
c) 81.42-18.4 =
__________
d) 4732.3 + 55 + 0.54 =
__________
e) 999.0 + 1.7 – 43.7 =
__________
f) 564,321 – 264,321 =
__________
g) 0.04216 – 0.0004134 = __________
Work Check
2-8
Name_______________________
Multiplication and Division In multiplying or dividing, the number of significant figures in the answer (regardless of the position of the decimal point) equals that of the quantity which has the smaller number of significant figures. EXAMPLE: multiplying:
EXAMPLE: dividing:
2.61 x 1.2 this has the smaller number of significant figures (2) 3.132 rounds off to → 3.1 has 2 significant figures 2.61 / 1.2 = 2.175 rounds off to → 2.2
5. Carry out the following multiplications, expressing your answer to the correct number of significant figures.
a) 27.88 x 0.00695 =
__________
b) 3.10 x 5428 =
__________
c) 3.00 x 0.4000 =
__________
d) 0.693 x 7.3x102 =
__________
e)
4317 0.88
__________
f)
(2.7x108 )(0.00149) (0.1500)
__________
g)
(8.4)(0.03) (147)(.11)
__________
(57332)(3.5x10 4 ) h) (185)(2x1012 )
__________
Work Check
2-9
Name_______________________
Mixed Practice – you must show the s.f on intermediate calcs to get credit!!! 1) (183 x 0.017) + 850. =
2)
(12.7 − 8.3) = (18.5 − 2.2)
3) (3.0 x 2.2) + (4 x 85) =
4)
(0.127 − 0.038) = 0.0445
3.24x10 −5 5) = (187 + 27)
6)
(438 + 825) = 1.234x10 −6
4.02x108 + 385 = 7) 5 1.4x10 4.02x108 + 385 = 8) −3 1.4x10
9)
(14.8 − 12.5) = 12.5
(0.01020)(4.3 x10 4 ) 10) = (16 − 12)
11)
(83.4 − 27.4) = 0.0432 Work Check
2-10
