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
wood alcohol
chromium
water
hydrogen
carbon
nitrogen
oxygen
gold
sugar
salt
air
sulfur
magnesium
nickel
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: ______
pure water: _________
an apple: ____________
nitric acid: ___________
tossed salad: __________
granite: ______________
wood: _______________
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: ____________________
stomach acid: ______________ mercury: ______________________________
an orange: _________________ water & instant coffee: ___________________
a pencil: __________________ carbon particles & sugar: ______________
hydrogen: _________________ methane: _________________________
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)
Work Check
2-3
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 hearburn.
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.
Water freezes at 0°C.
Fireworks produce colors.
Alka-Seltzer gives off carbon dioxide when added to water.
Clouds form in the sky.
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
6. dirt
2. filtered green tea
7. sausage pizza
3. gravel
8. laundry bleach
4. Lucky Charms®
9. store-bought milk
5. salt
10. gold
INSTRUCTIONS: Classify each of the following as an element [E], a compound [C], or a
mixture [M].
11. calcium
16. pancake syrup
12. nitrous oxide
17. carbon monoxide
13. seawater
18. silver
14. sugar
19. ice
15. a chocolate sundae
20. a Big Mac®
INSTRUCTIONS: Classify each of the following properties of matter as physical [P] or
chemical [C].
21. Color
26. Reacts violently with chlorine
22. Density
27. Good conductor of heat
23. Burns easily (flammable)
28. Dissolves readily in water
24. Not affected by acids
29. Melts at 145 °C
25. Boils at 450 °C
30. Malleable (bendable)
INSTRUCTIONS: Classify each of the following changes in matter as physical [P] or
chemical [C].
31. Grinding chalk into powder
36. Burning gasoline
32. Dissolving salt in water
37. Hammering gold into foil
33. Dissolving zinc in acid
36. Melting ice
34. Tearing a piece of paper
39. photosynthesis by plants
35. Stretching copper into wire
40. Making hydrogen from water
2-5
Work Check
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
_____
Work Check
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) 8.6x10-4 x 1.9x102 = __________
f)
4317
0.88
(2.7x108 )(0.00149)
g)
(0.1500)
__________
__________
h)
(8.4)(0.03)
147
__________
i)
(0.1070)(328)
(0.01244)
__________
j)
(57332)(3.5x104 )
(185)(2x1012 )
__________
Work Check
2-9
Name_______________________
Mixed Practice
1) (1.3 + 9.7)(22) =
2) (183 x 0.017) + 850. =
3)
(12.7 − 8.3)
=
(18.5 − 2.2)
4) (3. x 2.2) + (4 x 85) =
5)
(0.127 − 0.038)
=
0.0445
3.24x10−5
6)
=
(187 + 27)
7)
(438 + 825)
=
1.234x10−6
 4.02x108 
 + 385 =
8) 
5 
 1.4x10 
 4.02x108 
 + 385 =
9) 
−3 
1.4x10


10)
(14.8 − 12.5)
=
12.5
(0.01020)(4.3 x10 4 )
11)
=
(16 − 12)
12)
(83.4 − 27.4)
=
0.0432
Work Check
2-10