Chem 30A – Exam #2 (Chapter 5,6,8)
Name: __________________
04_05.JPG
H = 1.001
1.
C = 12.01
N = 14.01
O = 16.00
Draw the Lewis dot structure for
(a)
PCl3
Cl = 35.45
(b)
SO3
Cl
Cl
O
P
O
S
Cl
2.
O
Write the balanced equation for the following
(a)
P (s) + O2 (g) → P2O5 (s)
4 P + 5 O2 → 2 P2O5
(a-1)
For the reaction above, what type of reaction is it? redox
(b)
BaCl2 (aq) +
Fe2(SO4)3
(aq)
→
BaSO4 (s)
+
FeCl3
(aq)
3 BaCl2 + Fe2(SO4)3 → 3 BaSO4 + 2 FeCl3
(b-1) For the reaction above, what type of reaction is it? precipitation
P = 30.97
S = 32.07
3.
Name the following compounds
(a)
P2O5
diphosphorous pentoxide
(b)
CCl4
carbon tetrachloride
(c)
N2O
dinitrogen monoxide
4.
What does STP stand for?
5.
What are the values associated with STP? T = 0oC and P = 1 atm.
6.
What is the volume of 3.0 mole of He at 760 torr and 30oC?
standard temperature and pressure
Problem recognition:
PV = nRT
moles given → likely ideal gas law problem.
T = 30oC = 303 K
P = 760 torr = 1 atm
V = nRT / P = (3.0 mol)(0.0821 L atm / mol K)(303K) / 1 atm = 74.6 L = 75 L
7.
What is the molar mass of N2O?
MM of N2O = mass of all N + mass of all O
= 2 (14.01) + 16.00
= 44.02 g / mol
8.
What is the molar volume of N2O at STP?
22.4 L / mol
9.
What value is associated Avogadro’s number?
6.02 x 1023
10.
How many moles are present in 7.77 g of N2O?
7.77 g (1 mole / 44.02 g) = 0.177 mole
11.
What is the mass of 777 molecules of N2O?
777 molecules ( 1 mole / 6.02 x 1023 molecules)(44.02 g / mol) = 5.68 x 10-20 g
12.
At STP, what is the mass of 77 liters of N2O?
77 L ( 1 mole / 22.4 L )( 44.02 g / mol ) = 150 g
13.
If 3.9 g of a gas has a volume of 22 L at STP, what is its molar mass?
molar mass = mass / mole
= 3.9 g / 0.9821 mole
= 4.0 g / mol
22 L ( 1 mole / 22.4 L) = 0.9821 mole
14.
If a tank of gas has a pressure of 600. torr at 25oC, assuming constant volume, what is the temperature of
the gas, in Celsius, if the pressure increases to 1000. torr?
Problem recognition: 2 sets of conditions, probably combine gas law problem
constant volume = Gay-Lussac’s Law
P1 / T1 = P2 / T2
(600. torr) / (298K) = (1000. torr) / T2
T2 = 497 K = 224oC
15.
A tank containing a mixture of hydrogen, nitrogen, and helium gas has a pressure reading of 33 psi. If
the pressures of hydrogen and nitrogen are 12 and 7 psi respectively, what is the pressure of the helium gas?
Dalton’s law of partial pressure
Ptotal = 33 psi = 12 psi + 7 psi + Phelium
Phelium = 14 psi
16.
What does the inside pressure become if an aerosol can with an initial pressure of 5.4 atm is heated in a
fire from 20oC to 600oC?
Problem recognition: 2 sets of conditions, probably combine gas law problem
assuming constant volume = Gay-Lussac’s Law
P1 / T1 = P2 / T2
(5.4 atm) / (293K) = P2 / (873K)
P2 = 16 atm
17.
Describe Boyle’s Law.
The pressure and volume of a gas are inversely related under constant temperature.
18.
Under what condition(s) do real gas behavior deviate from an ideal gas?
pressure
Given this balanced equation, N2 + 3 H2 → 2 NH3
low temperature and high
19.
How many moles of N2 is needed to react fully with 7.2 g of H2?
(7.2 g H2) ( 1 mole / 2.02 g H2) ( 1 N2 / 3 H2) = 1.2 mole N2
20.
What is the theoretical yield of NH3 (in grams) that can be produced from 12.2 L of N2 at STP?
(12.2 L N2) ( 1 mole / 22.4 L) ( 2 NH3 / 1 N2 ) ( 17.04 g / 1 mol NH3) = 18.6 g NH3
21.
List the reactant(s) from the above balanced equation. N2 and H2
22.
What is an aqueous solution?
An aqeous solution is a solution containing one or more compounds dissolved in water.
23.
Between boron (B), carbon (C), and nitrogen (N), which is the most least electronegative element?
(circle your answer) -- electronegativity decreases going left on the periodic table.
24.
Given the electronegativity of phosphorous and chlorine are 2.1 and 3.0 respectively, is the P-Cl bond
polar or non-polar? (circle the answer) difference in electronegativity (3.0 – 2.1 = 0.9) greater than 0.5
25.
Attribute the following properties to either ionic (I) or molecular (M) compounds.
(a)
low melting point
molecular
(b)
many are water soluble
ionic
(c)
can be gases, liquids, or solids
molecular
26.
Predict the solubility of the following compounds in water as either soluble (S) or insoluble (I).
(a)
CaCO3
insoluble
soluble (according to text)
(b)
CaSO4
(c)
Li2SO4
soluble
(d)
CaCl2
soluble
(e)
AgCl
insoluble
27.
List in order of increasing strength the following types of intermolecular forces. Dipole-dipole
interaction, Hydrogen bonding, and London dispersion forces.
L.D.F → D.D. → Hydrogen bonding
28.
A weather balloon is filled with helium to a volume of 225 L at 18oC and 763 mmHg. The balloon
ascends to an altitude where its volume rises to 1365 L and the temperature is -55oC. What is the pressure at
this altitude?
2 sets of conditions, combine gas law
P1 V1 / T1 = P2 V2 / T2
(763 mmHg) ( 225 L) / (291K) = P (1365 L) / 218 K
P = 94.2 mmHg