Chemistry 112
First Hour Exam
Name:____________
Please show all work for partial credit
1. (10 points)
a millimeter is what part of a meter? A millimeter = 1x10-3 or .001 meter
a nmole is what part of a mole? A nmole = 1x109 or .000000001 mole
How is 106 abbreviated?
106 = mega = M
How is 10-3 abbreviated?
10-3 = milli = m
a deciliter is what part of a liter? A deciliter = 1x10-1 or .1 liter
2. A. (6 points) How many significant figures in the following numbers?
.00456
3 sig fig
Leading zeros aren’t significant
4.05600
6 sig fig
Trailing zeros after a decimal are significant
4.56000
6 sig fig
Trailing zeros after a decimal are significant
B. (4 points) How many significant figures should you have in the answer to the
following calculation?
.0104 moles/(36.46 mL - .04 ml)
36.46- .04 = 36.42 this number has 4 sig fig
The actual division then is .0104 (3 sig fig - the leading zero is not significant) divided by 36.42 (4
sig fig). The overall sig fig in a multiplication or division should be the same as the lowest sig fig of any
number in the calculation so you use the 3 sig fig from the numerator.
3. A (5 points) I drive am driving at 65 miles per hour. What is this in kilometers per second?
65 mile
1 km
1 hr
1 minute
×
×
×
= 2.9 x10 − 2 km / sec
hr
.62137 mi 60 minutes 60 seconds
B. (5 points) The pressure in my tires is 32 lbs/in2. What is that in g/cm2
32 lbs
1 kg
1000 g
1 in
1 in
×
×
×
×
= 2.2 × 10 3 g / cm2
2
in
2.2046 lbs
1 kg
2.54 cm 2.54 cm
2
4. (10 points) What is the difference between an ionic bond and a covalent bond. What kinds
of atoms are involved in each bond?
Covalent bond - electrons shared between the two atoms- atoms are held together by the electrons
shared between them - both atoms are nonmetals
Ionic bond - electrons are not shared equally between the atoms. One atom, the anion, has one
or more electrons more than its atomic number, giving it a negative charge, while a second atom, the cation,
has one or more electrons less than its atomic number, giving it a positive charge. The atoms are held
together by the electrostatic attraction between the negatively charged anion and the positively charged
cation. The cation is usually a metal while the anion is a nonmetal.
5. (5 points) What is the chemical name of the element with an atomic mass of 41 and an
atomic number of 20. Do you think this is the most common isotope of this element?
41
20
Ca
If you look on the periodic table you see that the average atomic weight of Ca is 40.08 which is
40
almost an entire atomic mass unit less than this isotope. Thus the most common isotope is probably 20
Ca
41
and the 20
Ca isotope is probably not common.
6. (10 points) Give the name (NOT abbreviations) of:
Any alkali metal
Lithium, Sodium, Potassium, Rubidium, Cesium, or Francium
An inert gas in the third period
Argon
An alkaline earth metal in the second period
Beryllium
Any transition metal Any metal between Scandium, Zinc, Lanthanum, and Mercury
Fluorine is a member of which chemical family
halide or halogen
7. Name the following compounds (3 points each)
SF6
Sulfur hexafluoride
FeCl2
Iron(II) chloride
K2SO4
Potassium sulfate
Give the molecular formula of the following compounds (3 points each)
Dinitrogen tetraoxide N2O4
Calcium chloride CaCl2
3
8. (10 points) What is the % composition of each of the elements in Sr(OH)2
Grams of each element in 1 mole of compound
Sr = 87.62 x 1 =
O = 16.00 x 2 =
H = 1.008 x 2 =
total of atomic masses =
87.62
32.00
2.016
121.636
divide mass of individual elements by total mass
% Sr = 87.62/121.636 =
% O = 32.00/121.636 =
% H = 2.016/121.636 =
72.03%
26.31%
1.657%
9. (10 points) A compound has a molecular weight of 46.068 contains 52.17%C, 13.13% H
and 34.73% oxygen. What is the molecular formula of this compound?
Multiply molecular weight by percent composition to find mass of each element in compound:
46.068 x .5217 = 24.0337 g C
46.068 x .1313 = 6.0487 g H
Divide mass of each element in compound by atomic mass of element to find number of moles of element
in compound.
24.0337/12.01 = 2.00 = 2 moles
6.0487/1.008 = 6.001 = 6 moles
15.999/16.00 = .99994 = 1 mole
C2H6O
10. A (4 points) Balance the following equation:
K
O
H
K
O
H
K(s) + H2O(l)6 KOH(aq) + H2(g)
K(s) + H2O(l)6 KOH(aq) + H2(g)
1
=1
1
= 1
2
… 1
2
K(s) + H2O(l)6 KOH(aq) + ½ H2(g)
1
=1
1
= 1
2
= 1
1
Balanced
Balanced
Not balanced unless use coefficient of ½ for H2, then
Balanced
Balanced
Balanced
As a general rule you should not have fractional coefficients so multiply all the numbers by 2 to get rid of
the ½
2K(s) + 2H2O(l)6 2KOH(aq) + 1 H2(g)
4
B (6 points) Give a balanced equation for the following reaction:
Solid iron (III) sulfide + hydrogen chloride gas reacts to give solid iron(III) chloride and
hydrogen sulfide gas.
iron (III) sulfide = Fe2S3
hydrogen chloride = HCl
iron(III) chloride = FeCl3
hydrogen sulfide = H2S
Next put in equation form and add the physical states
Fe2S3(s) + HCl(g) 6FeCl3(s) + H2S(g)
Now start balancing
Fe2S3(s) + HCl(g) 6FeCl3(s) + H2S(g)
Fe
2
1
(Need 2 FeCl3 on right to balance)
Fe
Cl
Fe2S3(s) + HCl(g) 62FeCl3(s) + H2S(g)
2
2
1
6
Fe
Cl
S
Fe2S3(s) + 6HCl(g) 62FeCl3(s) + H2S(g)
2
2
6
6
3
1 (Need 3 H2S on right to balance)
Fe
Cl
S
H
Fe2S3(s) + 6HCl(g) 62FeCl3(s) + 3H2S(g)
2
2
6
6
3
3
6
6 Balances with no changes, hooray!
Final balanced equation:
Fe2S3(s) + 6HCl(g) 62FeCl3(s) + 3H2S(g)
(Need 6 HCL on left to balance)