Download Practice Test 3: Answer Key

Practice Test 3( Net Ionics, Ch # 6,ch8,ch11)
KEY
1. The empirical formula of a compound is CH. The molar mass of this compound is 78.0,
then the molecular formula is
A) C2H2
B) C5H18
C) C6H6 ( 78.0/14=6)***
D) No correct answer given
2.
A)
B)
C)
D)
The molar mass of MgCl2 is
95.21 g***
59.76 g
119.5 g
125.8 g
3.
A)
B)
C)
D)
How many moles are contained in 2.54 g Cu?
0.0400 mol (g/MM)***
25.0 mol
161 mol
no correct answer given
4.
A)
B)
C)
D)
The number of oxygen atoms in 7.8 g of O2 is
2.93 x 1023 ( 78.0 g x1/32.00 g x 6.022 x1023 x 2 atoms/1 molecule) ***
1.47 x 1023
5.86 x 1023
0.488
5.
A)
B)
C)
D)
Which one of the following could not be an empirical formula?
CH2
CH4
C2H5
C2H6 ( It can be reduced further to CH3) ***
6.
A)
B)
C)
D)
One mole of hydrogen atoms contains
2.0 g of hydrogen
6.022 x 1023 atoms of hydrogen ***
1 atom of hydrogen
12 g of carbon-12
1
7.
A)
B)
C)
D)
For the reaction 2 H2 + O2  2 H2O + 572.4kJ, which of the following is not true?
The reaction is exothermic.
572.4 kJ of heat are liberated for each mole of water formed.***
Two moles of hydrogen react with 1 mol of oxygen.
572.4 kJ of heat are liberated for each 2 mol of hydrogen reacted.
8. Choose the set of coefficients which balances the chemical equation given below.
N2O5 + B2O3 + H2O  B3N3H6 + O2
A) 6, 5, 5, 2, 15
B) 3, 3, 3, 5, 2
C) 3, 3, 6, 2, 15 ***
D) 2, 1, 1, 5, 1
9.
A)
B)
C)
D)
All of the following are endothermic except
boiling water
melting ice
condensing water vapor ***
reaction inside an ice pack
10.
A)
B)
C)
D)
What is the mass in grams of 0.30 mol of BaSO4?
7.0 x 103 g
0.13 g
70. g ( mol x 233.37 (MM)) ***
700.20 g
11.
A)
B)
C)
D)
The number of moles in 1.00 kg NaCl is
1000
1000 x 58.44
1.00/(58.44 x 1000)
1000/58.44 *** ( Convert kg to g)
2
12. How many moles of SO2 can be produced from 20.0 g of H2S?
2 H2S + 3 O2  2 SO2 + 2 H2O
A) 0.312
B) 2.00
C) 20.0
D) 0.587 9 2.00 g x 1mol/34.07 x 2mol/2 mol) ***
*********************************************************************
13.
What volume will 3.00 L of a gas occupy if the temperature is changed from 30°C to
90°C (P is constant)?
A)
1.00 L
B)
9.00 L
C)
2.50 mL
D)
no correct answer given ( V1/T1= V2/T2)
14.
A)
B)
C)
D)
The pressure exerted by a mixture of an ideal gas is given by
Boyle's Law
Charles's Law
Gay-Lussac's Law
Dalton's Law ***
15.
Given 0.838 L of NH3 at 30.0°C. At what temperature will the NH3 have a volume of
2.00 L (P is constant)?
127 K
450°C ( T2= T1 V2/V1 , Subtract 273 from the answer you get to C) ***
71.6°C
12.6°C
A)
B)
C)
D)
16.
A)
B)
C)
D)
What is the partial pressure of O2 collected over water at 25°C and 630 torr? (Vapor
pressure of H2O at 25°C is 23.8 torr.)
654 torr
681 torr
606 torr ( 630- 23.8) ***
23.8 torr
16. Which of the following is not one of the principal assumptions of the Kinetic-Molecular
Theory for an ideal gas?
A) All collisions of gaseous molecules are perfectly elastic.
B) A mole of any gas occupies 22.4 L at STP. ***
C) Gas molecules have no attraction for one another.
D) The average kinetic energy for molecules is the same for all gases at the same
temperature.
3
17. If the pressure on 45 mL of gas is changed from 600. torr to 800. torr, the new volume
will be
A) 60 mL
B) 34 mL( V2= P1 V1/P2) ***
C) 0.045 mL
D) 22.4 L
18. Which of the graphs below represents the relationship between temperature and pressure
of an ideal gas, if volume and moles are held constant
A)
B)
C)
D)
A ***
b
c
d
19.
A)
B)
C)
D)
Which of the following defines standard conditions for a gas?
0K and 1 atm
273oC and 760 torr
273K and 760 torr ***
25oC and 1 atm
20.
A)
B)
C)
D)
Which pressure does not correspond to 1.25 atm?
950 torr
37.4 in. Hg
950 cm Hg *** ( it is given cms here)
1.27 kPa
21. At constant temperature the volume of a gas is inversely proportional to its pressure.
Which statement correctly expresses this relationship?
A) P1 P2

V1 V2
B) PV = constant ***
C) P = constant
V
D) V= P
4
22.
A)
B)
C)
D)
The combined gas law includes all of the following laws except
Boyles's Law
Gay-Lussac's Law
Charles's Law
Avogadro's Law ***
***************************************************************************
1. A compound called cadaverine is formed by action of bacteria on meat and fish. Analysis
shows that the elemental composition is C 58.8% , H 13.8 % and N 27.4 %. Determine the
empirical formula. Show all formulas and work to get full credit. – 6 points.
C= 58.8/12.01= 4.89/1.96=2.5 x 2=5
H=13.8/1.008=13/7/1.96=6.9=7 x 2= 14
N=27.4/14.01=1.96/1.96=1 x 2=2
EF: C5H14N2
2. A sample of ethylene chloride was analyzed to contain 6.00 g of C, 1.00 g of H, and 17.75 g of
Cl. Calculate the % composition of ethylene chloride. Show all formulas and work to get full
credit. – 6 points.
Total grams=24.75 g
% C =6.00/24.75 x 100=24.2 %
% H=1.00/24.75 x 100=4.04 %
% Cl= 17.75 /24.75 x 100=71.72 %
3. How many grams of steam and iron must react to produce 375 g of magnetic iron oxide,
Fe3 O4 ?
3Fe(s) + 4H2 O (g) →Fe3 O4 (s) +4H2 ( g)
Show all formulas and work to get full credit. – 6 points.
375 g Fe3 O4 x 1mol/231.55 g Fe3 O4 x 3mol Fe/ 1mol Fe3 O4 x 55.85 g Fe/1 mol Fe= 271 g
375 g Fe3 O4 x 1mol/231.5 g Fe3 O4 x 4 mol H2O/1mol Fe3 O4 x 18.02 g H2O/ 1 mol H2O= 117 g
5
4. Change the following word equations into formula equations, balance it give its total ionic, net
ionic equations.(6 points)
nickel(II) phosphate + sulfuric acid_________ nickel(II) sulfate + phosphoric acid.
Ni3(PO4)2 (aq) + 3 H2SO4 (aq) → 3 NiSO4 (s) + 2 H3PO4(aq)
TIE: 3 Ni2+ (aq) + 2 PO43-(aq) + 6 H+ (aq) + 3 SO42- (aq) → 3 NiSO4 (s) + 6 H+ (aq) + 2 PO43(aq)
NIE: 3 Ni2+ (aq) + 3 SO42- (aq) → 3 NiSO4 (s)
NIE: Ni2+ (aq) + SO42- (aq) → NiSO4 (s)
5. Balance the following equation and calculate how many moles of Cu can be formed from 5.0
moles of Al and 10.0 moles of CuSO4 . What is the limiting reactant and how much of the
excess reactant is left after the reaction?
Al + CuSO4 → Cu + Al2(SO4)3
Show all formulas and work to get full credit. – 10 points.
2Al + 3CuSO4
→
3Cu + Al2(SO4)3
5.0 mol Al x 3 mol Cu/2 mol Al =7.5 mol Cu
10.0 mol CuSO4 x 3 mol Cu/ 3mol CuSO4= 10.0 mol Cu
LR= Al , moles of Cu= 7.5
5.0 mol Al x 3 mol CuSO4/2 mol Al= 7.5 mol CuSO4 reacted
10.0 mol-7.5 mol=2.5 mol unreacted.
6. The volume of a gas filled balloon is 50.0L at 20.0 C and 742 torr. What volume will it occupy
at STP?- 6 points.
P1=742 torr, V1=50.0 L, T1=20 + 273= 293 K
P2 = 760 torr, V2= ? , T2= 273 K
P1V1/T1=P2V2/T2
V2= P1V1T2/ P2T1 = 48.9 L
6
7. When measured at 400 C and 630 torr, the mass of 691 mL of diethylether is 1.65 g.
Calculate the molar mass of diethyl ether. Show all your working to get full credit.(5 points)
T= 40 + 273=313 K
P=630 torr/760= 0.829 atm
V=691/1000=.691 L
Mass= 1.65 g
D= mass/V=2.39 g/L
M=DRT/P=74.04 g
7