Chemistry 112
First Hour Exam
Name:____________
Please show all work for partial credit
1. (10 points) Perform the following unit conversions.
350 nm to m
1x10 − 9 m
350nm ×
= 350 x10 − 9 m or 35
. x10 −7 m
nm
2 kHz to :Hz
2 kHz ×
1000Hz
1µHz
×
= 2 × 10 9 µHz
−6
1kHz
1 × 10 Hz
3.8 m to inches
38
. m×
10936
.
yd 36in
×
= 159.6in
1m
yd
6 lbs/in2 to kg/cm2
2
6 lbs
 1 in 
1kg
×
 = .421 kg cm2
2 ×
in
2.2046lbs  2.54 cm 
2. (10 points)
A. Give an example of a heterogenous mixture.
Hershey bar with almonds was #1, any mixture where you an see the individual
components of the mixture was accepted
B. Give two examples of solutions that are NOT liquids.
Brass, air, mayonnaise, steel and many others. It had to be a specific solid or gas
C. What are the two different types of pure substances?
Elements and compounds
3. (10 points) I have isolated a new element, Zehfusoid, abbreviated Zf. When I analyze this
element in a mass spectrometer I find it has two major isotopes, 47Zf and 49Zf. 1/4 of the atoms
are 47Zf and 3/4 of the atoms are 49Zf. What is the correct atomic mass for this element?
Since the atomic mass is an average that reflects the relative composition of the
individual isotopes 47(1/4) + 49(3/4) = 48.5
2
4. (10 points) Below are a the molecular formulas for a series of compounds, give the written
names of these compounds:
NaCl __Sodium chloride_______
PbO2 ___Lead(IV) oxide_______
Co2(SO4)2 __Cobalt(II) sulfate__
NO
___Nitrogen monoxide_____
P4O10 _Tetraphosphorous decaoxide
5. (10 points) Below are the names of several compounds, give their molecular formula
Aluminum Chloride ____NH4Cl__________________
Mangenese(III) oxide ___Mn2O3______________________
Hydrofluoric acid
___HF(aq)________________________
Sulfur trioxide
____SO3_______________________
N2O (laughing gas) __Dinitrogen monoxide__________________________
6. (10 points) Give the name or formula the following ions:
NH4+ _Ammonium___
Nitride___N3- ______
SO3-2 _Sulfite___________
Hydride ____H-________
OH-
__Hydroxide__________
3
7. (10 points)
A. What is the molar mass of the (NH4)2Cr2O7
(1.008x8) + (14.007x2) + (51.996x2) + (15.999x7) = 252.063
B. If I have 25 g of (NH4)2Cr2O7, how many moles do I have?
25g ×
1mole
= .0992 g
252 .063
C. If I have 25 g of (NH4)2Cr2O7, how many molecules do I have?
1 mole
6.022 x1023 molecules
25g ×
×
= 5.973x10 23 molecules
252 .063g
mole
8. ( 10 points)
A 0.75 g sample of a liquid is burned in a combustion analysis. In this analysis the
yields of CO2 and H2O were:
1.43 g CO2 .88g H2O
What is the empirical formula for this compound?
Find out how many g of C is in 1.43g of CO2
1.43g CO2 ×
1mole CO2
1mole C
12 g C
×
×
= .39 g C
44 g CO2
1 mole CO2 1 mole C
Find out how many g of H is in .88g H2O
.88g H2 O ×
1 mole H 2 O 2 moles H
1g H
×
×
= .098g
18 g H2 O 1 mole H 2 O 1 mole H
Calculate missing oxygen
.75 - .39 -.098 = .262g
Find moles of C, H, and O in compound
143
. g CO2 ×
1 mole CO2
1 mole C
×
= .0325mole C
44 g CO2
1 mole CO2
1 mole H2 O 2 moles H
×
= .098mole H
18 g H 2 O 1 mole H 2 O
1 mole O
.262g O ×
= .016mole O
16 g O
.88 g H 2 O ×
Divide by the smallest number of moles
C = .0325/.016 .2; H= .098/.016.6; O= .016/.016=1
C2H6O
4
9. (10 points) Balance the following equations:
N2(g) + H2(g) 6 NH3(g)
N2(g) +3 H2(g) 6 2NH3(g)
Fe2O3(s) + C(s) 6 Fe(s) + CO(g)
Fe2O3(s) + 3C(s) 6 2 Fe(s) +3 CO(g)
10. (10 points) I am performing the following reaction in a lab
2Al(s) + 3 Br2(l) 6 2 AlBr3(s)
If I start with 5 g of Al and 5 g of Br2 and have a 5 g yield of AlBr3, what was the % yield
for my reaction?
Yield of AlBr3 from 5g Al
5g Al ×
1 mole Al 2 mole AlBr3 26.98 + 3(79.9) g AlBr3
×
×
= 49.4 g
26.98 g Al
2 mole Al
1 mole AlBr3
Yield AlBr3 from 5g Br2
5g Br2 ×
1 mole Br2
2 mole AlBr3 29.98 + 3(79.9 ) g AlBr3
×
×
= 563
. g
79.9 x 2 g Br2
3 mole Br2
1 mole AlBr3
Lowest yield (5.63 g) is limiting reactant and theoretical yield
% yield = Actual/theoretical X 100% = 5/5.63 x 100% = 89.9%