Unit 2 – Measurements, Math, & the Mole
Nothing in life is to be feared. It is only to be understood. ~Marie Curie
Essential Skills / State Standards
1. Be able to use the correct number of Significant Figures for Lab measurements and for mathematical
calculations.
2. Perform calculations using scientific notation.
3. Know that 1 mole is set by defining 1 mole of Carbon-12 atoms weighs 12 grams.
4. One mole equals 6.02 x 10 23 particles (atoms or molecules)
5. Know how to determine the molar mass of a molecule from its chemical formula and a table of atomic
masses
6. Convert the mass of a substance to the number of moles and the number of particles.
Study Guide
(Your labs, worksheets, and homework should also be used) **You must show all your work for credit!**
1. Why are sig figs important to use when measuring?
They show how accurate the device is. You record all the units on the device, plus go one more digit that’s an
estimate. All those numbers count as significant figures.
2.
Record the measurement indicated with the correct number of sig. figs (both are in Cm).
3.5 cm
3.50cm
3. How many significant figures are in the following? Underline them too.
a. 1000 m
b. 3025000 cm
c. 0.00740 ml
d. 8740. m
1
4
3
4
e. 5400.0 g
5
4. Write the following in scientific notation:
a. 646 002 000 000 000 km
b. .000 000 000 0215 mm
5. Write the following in ordinary notation
a. 2.036 x 105 atoms
203,600 atoms
b. 6.548 x 10-4 molecules
0.0006548 molecules
6.46002 x 10
14 km
2.15 x 10
-11 mm
6. Perform the calculations; report your answers in both regular & sci. notation with sig figs.
a. (5400s)(3.5s)=
b.
34.95 g =
c. (6.1 x 103 g) (2.0 x 105 g)=
d. 9 x 106 cm =
= 19000 s2
11.169 cm3
= 1,200,000,000 g2
8 x 104 cm
3
9
2
Or
= 3.129 g/ cm
= 1.2 x 10 g
=100 or 1 x 102
1.9 x 104 s2
= 3.129 X 100 cm3
7. You find something that looks like a diamond that has a mass of 1.14 g and a volume of 0.56 mL. Real diamonds
have a density of 3.26 g/ml Use Sig Figs.
a) Calculate the density of this potential diamond.
b) How would you know if this is a real diamond?
Compare it to the density of 3.26,
D= Mass/ volume
it’s not real.
D = 1.14 g/ 0.56 mL
D= 2.0 g/ mL
c) Based on the density a real diamond, will it float or sink in water? Explain.
Diamonds would sink because the density of water is 1 g/ ml and diamonds are more dense at 3.26 g/ mL.
d) What volume would a real diamond be (see density) if it had a mass of 1.14 grams?
D = M/ V
3.26 g/ ml = 1.14/ V
V= .350 ml
8. Determine the type of metric measurement in each of the following (volume, length, density, mass, area):
Abbreviation
mm
m2
ml
g ÷ L
cm
cm3
L
Unit
millimeter
Meters
Milliliter
grams/Liter Centimeter Centimeter
Liter
squared
cubed
Quantity
length
Area
Volume
Density
Length
Volume
Volume
measured
9. Put the following metric terms in order from smallest to largest:
Meter, millimeter, kilometer, & centimeter,
millimeter, centimeter, meter, kilometer
10. Which metric unit would be best to measure the following?
a. the mass of a vitamin
b. the volume of a key
milligrams (mg)
milliliters (mL)
c. the width of a dime
millimeters (mm)
11. Perform unit conversion calculations using the SI system:
a. 4800 g to kg
b. 5 m to cm
c. 25 L to mL
4800 g
1kg
5m
100 cm
25 L
1 000 ml
1000g
1m
= 500 cm
= 4.8 Kg
d. 5 cm3 to ml
5 cm3
1 ml
1 cm3
1L
= 25,000 ml
= 5 mL
23
12. One mole of any substance contains ____6.02 x 10
____ particles (aka_ Avogadro’s_number).
One mole of any substance in chemistry also has an associated mass called molar mass which can be
found on the periodic table of elements. For example, the molar mass of C is 12.01 g/mol while the
molar mass of oxygen is 16.00 g/mol. The molar masses of each substance are different because the
size/ mass of each substance is different.
13.Calculate the molar mass of the following:
a) Ca
= 40.08 g/mol
b) Cl2 = 70.90 g/mol
How to determine:
Use the periodic table
2(35.45 g/mol)
c) CO2 = 44.01 g/mol
d) Ca(OH)2 = 74.10 g/mol
C= 12.01
(O) 2= 32.00
40.08 g/mol + 2(16.00 g/mol)
+ 2(1.01 g/mol)
14. Write the “mole map” that allows you to go between grams, moles, and atoms. Include the conversion factors.
Grams
molarmass
Moles
Avogadro'sNumber
15. Convert the following to moles: Use Sig Figs
a) 824g of NH3
b) 43.6g of O2
molar mass NH3 = 17.04 g/mol
824 g NH3
= 48.4
1 mol NH3
17.04 g NH3
mol NH3
molar mass O2 = 32.00 g/mol
43.6 g O2
= 1.36
1 mol O2
32.00 g O2
mol O2
Atoms/Molecules
c) 1.2 x 10
24
molecules of CaCl2
1.2 x 1024 molecules
= 2.0
mol Cl2
1 mol
6.02 x 1023 molecules
16. Convert the following to grams: Use Sig Figs
a) 3.00 moles of CO2
b) 0.76 moles of H2
molar mass CO2 = 44.01 g/mol
3.00 mol CO2
= 132
g CO2
44.01 g CO2
1 mol CO2
molar mass H2 = 2.02 g/mol
0.76 mol H2
= 1.5
g H2
2.02 g H2
1 mol H2
c) 3.01 x 10
12
molecules of H20
molar mass H2O = 18.02 g/mol
3.01 x 1023
molecules H2O
=
9.01 g H2O
17. Given 4.50 g of CO2, how many molecules do you have? Use Sig Figs
6.02 x 1023 molecules
4.50 g CO2
1 mol CO2
=6.16 x 10 22 molecules
44.01 g
1 mol CO2
1 mol H2O
6.02 x 1023
molecules H2O
18.02 g H2O
1 mol H2O