Download WORKSHOP: Matter and Working with Significant Figures

 Chem 305
Instructor’s Edition
Name_______________________ 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.
is not
2. In a compound the (atoms/molecules) are (chemically/physically) combined so
atoms
chemically
that the elements that make up the compound (retain/lose) their identities and
lose
(do/do not) take on a new set of properties.
do
3. The smallest identifiable unit of a compound is a(n) molecule ________ ,
which is made up of atoms __________ which are chemically bonded.
4. (True or False): A mixture is always made up of a combination of elements.
False
5. In a mixture, the substances (lose/retain) their identities.
retain
6. In a mixture the substances involved (can/cannot) be separated by a simple
physical process.
can
In a compound the elements involved (can/cannot) be separated by a simple
physical process
cannot
because the elements are (physically combined/chemically bonded).
chemically bonded
7. (True or False): An element can be broken down into a simpler substance.
False (protons, neutrons & electrons don’t have properties of a “substance”.
8. The smallest identifiable unit of an element is a(n) atom ____________ .
9. From the following list of substances, circle the ones that are elements:
silver #
carbon dioxide
wood alcohol
chromium#
hydrogen #
carbon #
nitrogen #
water
oxygen #
gold #
sugar
salt
air
sulfur #
magnesium #
nickel #
10. How would you separate sand and water in a mixture?
Filter the mixture. Water will flow through the filter but sand will be trapped in the filter.
12. Explain how to separate the sugar and water in a solution of sugar and water.
Let the water evaporate. (This can be done faster by heating). The solid sugar
will be left behind.
2‐1 Adapted from Lalibert, 7/17/08
Work Check
Name_______________________ 13. Classify the following as pure substances (pure) or as mixtures (mix):
air: mix _________
gasoline: mix ___________
orange juice: mix _____
tap water: mix _____
sugar: pure __________
gold: pure ____________
mercury: pure _______
oxygen: pure __________
salt water: mix ________
14.Classify the following as heterogeneous (Het) or as homogeneous (hom):
sand & salt mix: het ____
hydrogen: hom _______
iron: hom ____________
salt water: hom ______
filtered air: hom ______
iron with rust: het ____
pure water: hom _____
an apple: het __________
nitric acid: hom _______
tossed salad: het _______
granite: het____________
wood: het ____________
15.Classify the following as an element, a compound,
a homogeneous mixture, or a heterogeneous mixture:
aluminum: element ___________ raisin bread: hetero mix __________________
carbon dioxide: compound _____ pure water: compound _______________
sugar and water: homo mix ____ sodium chloride: compound ____________
stomach acid: homo mix _______ mercury: element _______________________
an orange: hetero mix ________ water & instant coffee: homo mix ___________
a pencil: hetero mix __________ carbon particles & sugar: hetero mix ______
hydrogen: element ___________ methane: compound _________________
gasoline: homo mix __________ neon: element ___________________
Work Check
2‐2 Adapted from Lalibert, 7/17/08
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.
X Hydrochloric acid reacts with magnesium to produce hydrogen gas.
X A piece of copper is cut in half.
X A sugar cube is ground up.
X Water is heated and changed to steam.
X Iron rusts. (reacts with oxygen)
X Ethyl alcohol evaporates.
X Ice melts.
X Milk sours (goes bad). Milk sugar (lactose) turns to acid
X Sugar dissolves in water.
X Sodium and potassium react violently with water.
X An antacid relieves hearburn.
X Grass grows on a lawn.
X A tire is inflated with air.
X Oxygen and hydrogen combine to form water.
X Water is absorbed by a paper towel.
X Ethyl alcohol boils at 79°C.
X Paper burns.
X Water freezes at 0°C.
X Fireworks produce colors.
X Alka-Seltzer gives off carbon dioxide when added to water.
X Clouds form in the sky.
X Work Check
2‐3 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
hom
6. dirt
het
2. filtered green tea
hom
7. sausage pizza
het
3. gravel
het
8. laundry bleach
hom
4. Lucky Charms®
het
9. store-bought milk
hom
5. salt
hom
10. gold
hom
INSTRUCTIONS: Classify each of the following as an element [E], a compound [C], or a
mixture [M].
11. calcium
E
16. pancake syrup
M
12. nitrous oxide
C
17. carbon monoxide
C
13. seawater
M
18. silver
E
14. sugar
C
19. ice
C
15. a chocolate sundae
M
20. a Big Mac®
M
INSTRUCTIONS: Classify each of the following properties of matter as physical [P] or
chemical [C].
21. Color
P
26. Reacts violently with chlorine
C
22. Density
P
27. Good conductor of heat
P
23. Burns easily (flammable)
C
28. Dissolves readily in water
P
24. Not affected by acids
C
29. Melts at 145 °C
P
25. Boils at 450 °C
P
30. Malleable (bendable)
P
INSTRUCTIONS: Classify each of the following changes in matter as physical [P] or
chemical [C].
31. Grinding chalk into powder
P
36. Burning gasoline
C
32. Dissolving salt in water
P
37. Hammering gold into foil
P
33. Dissolving zinc in acid
C
36. Melting ice
P
34. Tearing a piece of paper
P
39. photosynthesis by plants
C
35. Stretching copper into wire
P
40. Making hydrogen from water
C
2‐4 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
_____6
b) 0.00084
_____2
c) 5.001
_____4
d) 0.0620
_____3
e) 107.010
_____6
f)
_____2-4 (ambiguous)
g) 3.400 x 103
_____4
h) 3.40 x 103
2‐5 3400
_____3
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 _______________ 673.15
4 sig figs _______________ 50.07
3 sig figs _______________ 673
3 sig figs
_______________ 50.1
2 sig figs _______________ 6.7 x 102
2 sig figs
_______________ 5.0 x 101
1 sig fig
_______________ 5 x 101
1 sig fig
_______________ 7 x 102
4. Round the value 273.84 to:
5. Round the value 48372000 to:
4 sig figs _______________ 273.8
4 sig figs _______________ 4.837 x 107
3 sig figs _______________ 274
3 sig figs _______________ 4.84 x 107
2 sig figs _______________ 2.7 x 102
2 sig figs _______________ 4.8 x 107
1 sig fig
_______________ 3 x 102
1 sig fig
_______________ 5 x 107
Work Check
2‐6 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 =
__________ 271 (calc & corr)
b) 2.222 + 2.22 + 2.2 =
__________ 6.642 (calc)  6.4 (corr)
c) 81.42-18.4 =
__________ 63.02 (calc)  63.0 (corr)
d) 4732.3 + 55 + 0.54 =
__________ 4787.84 (calc)  4788 (corr)
e) 999.0 + 1.7 – 43.7 =
__________ 957 (calc)  957.0 (corr)
f) 564,321 – 264,321 =
__________ 300,000 (ambiguous)  3.00000x105 or 300,000.
g) 0.04216 – 0.0004134 = __________ 0.0417466 (calc)  0.04175 or 4.175x10-2 (corr)
Work Check
2‐7 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 =
__________ 0.193766 (calc)  0.194 (corr) OR 1.94x10-1
b) 3.10 x 5428 =
__________ 16826.8 (calc)  1.68 x 104 (corr) NOT 16800
c) 3.00 x 0.4000 =
__________ 1.2 (calc)  1.20 (corr)
d) 0.693 x 7.3x102 =
__________ 505.89 (calc)  5.1x102 (corr) NOT 510
e) 8.6x10-4 x 1.9x102 = __________ 0.1634 (calc)  0.16 (corr) OR 1.6x10-1 (corr)
f)
4317
0.88
g)
(2.7x108 )(0.00149)
__________ 2.682 x 106  2.7 x 106
(0.1500)
h)
(8.4)(0.03)
147
__________ 0.001714  0.002 OR 2 x 10-3
i)
(0.1070)(328)
(0.01244)
__________ 2821.2  2.82 x 103
j)
(57332)(3.5x10 4 )
(185)(2x1012 )
__________ 5.423 x 10-6  5 x 10-6
__________ 4905.7  4.9 x 103
Work Check
2‐8 Name_______________________ Mixed Practice
1) (1.3 + 9.7)(22) = (11.0)(22) = 242  2.4 x 102
2) (183 x 0.017) + 850. = 3.111 + 850. = 853.11  853 OR 8.53 x 102
3)
(12.7  8.3)
4.4
=
= 0.26994  0.27 OR 2.7 x 10-1
(18.5  2.2) 16.3
4) (3. x 2.2) + (4 x 85) = 6.6 + 340 = 346.6  3 x 102
5)
0.089
(0.127  0.038)
=
= 2.0 don’t forget the trailing zero!
0.0445
0.0445
3.24 x10 5
3.24x10 5
6)
=
= 1.514 x 10-7  1.51 x 10-7
(187  27)
214
7)
(438  825)
1263
= 1.0235008 x 109  1.024 x 109
6 =
1.234x10
1.234x10 6
 4.02x108 
  385 = 2871.4 + 385 = 3256.4  3.3 x 103
8) 
5 
1.4x10


 4.02x108 
  385 = 2.87142854x1011 + 385 = 2.87143239x1011  2.9 x 1011
9) 
3 
 1.4x10 
10)
(14.8  12.5)
2.3
=
= 0.184  0.18 OR 1.8 x 10-1
12.5
12.5
438.6
(0.01020)(4.3x10 4 )
11)
=
= 109.65  1 x 102
(16  12)
4
12)
(83.4  27.4)
56.0
=
= 1296.3  1.30 x 103 don’t forget the trailing zero!
0.0432
0.0432
Work Check
2‐9