Chemistry 2202
Review for Unit 1 Test 1
For questions involving calculations, show all work and give the correct number of significant digits and units in your
answer.
1. Complete the table:
Isotope name
Isotope
notation
Atomic #
Mass #
# protons
#neutrons
38
90
95
82
87
230
241
208
38
90
95
82
49
140
146
126
Strontium-87
Thorium-230
Americium-241
Lead-208
2. Bromine exists as two naturally occurring isotopes: Bromine-79 (78.91 u) and Bromine-81 (80.92 u). These
isotopes have isotopic abundances of 50.69 % and 49.31 % respectively. Calculate the average atomic mass of
bromine.
WAM = (78.91 u x 0.5069) + (80.92u x 0.4931)
= 39.9995 u + 39.9017 u
=79.90 u
3. The average atomic mass of silicon is 28.090 u. Silicon-28 has a mass of 27.977 u and relative abundance of
92.23 %. Silicon-29 has a mass of 28.976 u and relative abundance of 4.67 %. Find the mass of the silicon-30
isotope.
Abundance silicon-30:
LET x = mass of silicon-30
= 100.00% – 92.23%-4.67%
= 3.10%
WAM
= 28.090 u = (27.977 u x 0.9223) + (28.976 u x 0.0467 ) + (0.0310x)
28.090 u = 25.803 u + 1.3532 u + 0.0310x
28.090 u = 27.1563 u + 0.0310x
28.090 u - 27.1563 u =0.0310x
0.9337 u = 0.0310x
X=30.12 u
4. Match the following symbol to the quantity (Write the letter in the space provided)
a. Mass
a
m
b. Amount (in moles)
e
M
c. Volume
f
MVSTP
d. Avagadro’s number
b
n
e. Molar mass
d
NA
f. Molar volume
c
v
5. Who developed the concept of the mole? Avagadro
6. Calculate the molar mass for each of the following: No need to show workings for this question only.
a. Water
MH2O = 18.02 g/mol
b. CO2(g)
MCO2 = 44.01 g/mol
c. Ca(CH3COO)2(s)
M Ca(CH3COO)2 = 158.18 g/mol
d. Glucose
MC6H12O6 = 180.18 g/mol
7. How many decimal places should you include in molar masses calculated from the periodic table?
You should always include two places past the decimal ex. MNaOH= 40.00 g/mol
8. Rearrange the formula for the quantity indicated:
9. Convert the following:
a. 6.000 x 1024 particles of H2O to amount(in moles)
Answer:
b. 0.125 mol of N2(g) to number of particles
Answer:
c. 450 g of NaCl(s) to amount (in moles)
Answer:
d. 1.345 mol CO2(g) to mass
Answer:
e. 25.0 L at STP of ammonia to amount(in moles)
Answer:
f. 14.2 mmol of H2S(g) to volume at STP
Answer:
10. These questions involve the application of more than one of the “mole” formulas.
a. What mass of propane, C3H8(g) would be found in 25.0 L of the gas at STP?
Answer:
b. How many molecules of water would be in a 36.0 kg sample?