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Quantitative Chemistry
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Question 1
What is the mass in grams of one molecule of
ethanoic acid CH3COOH?
0.1
1 x 10-22
3.6 x 1025
60
Wrong Answer!
Molar mass of CH3COOH is 24 + 4 + 32 = 60
Question 2
Which is not a true statement?
One mole of methane
contains four moles of
hydrogen atoms.
One mole of 12C has a
mass of 12.00g.
One mole of hydrogen
gas contains 6.02 x 1023
atoms of hydrogen.
One mole of methane
contains 75% of carbon
by mass.
Wrong Answer!
1 mole of hydrogen gas contain 6 x 1023 molecules of
hydrogen gas. Since 1 mole of hydrogen is made up of 2
H atoms, 1 mole of hydrogen gas contains 2 x 6 x 1023
atoms.
Question 3
Which sample has the greatest mass?
1.0 mol N2H4
2.0 mol N2
3.0 mol NH3
25.0 mol H2
Wrong Answer!
A: 1 x (28+4) = 32g
B: 2 x 28 = 56g
C: 3 x (14+3) = 51g
D: 25 x 2 = 50g
Question 4
Which one of the following statements about SO2
is/are correct?
I. One mole of SO2 contains 1.8 x 1024 atoms
II. One mole of SO2 has a mass of 64g
Both I and II
Neither I nor II
I only
II only
Wrong Answer!
SO2 is made up of 3 atoms, hence 1 mole of SO2
contains 3 x 6 x 1023 atoms.
Molar mass of SO2 = 32 + 32 = 64.
Question 5
2Cl2 represents:
two chlorine molecules
two chloride ions
two chlorine atoms
four free chlorine atoms
Wrong Answer!
2Cl2 represents two chlorine molecules : Cl-Cl and Cl-Cl
Question 6
Which one of the following equations is not
correctly balanced?
Ca(s)+2H+(aq)
Ca 2+(aq)+H2 (g)
Mg(s)+ H2O(l)
Mg(OH)2 (aq)+H2(g)
Fe 2+(aq)+Ag+(aq)
Fe3+(aq)+ 2Cl-(aq)
Fe 2+(aq)+ Cl2 (g) 
Fe3+(aq)+ 2Cl-(aq)
Wrong Answer!
The charge is not balanced.
Question 7
Sulfuric acid and sodium hydroxide react together
according to the equation?
H2SO4(aq) + 2NaOH(aq)  Na2SO4(aq) + 2H2O(l)
What volume of 0.250 moldm-3 NaOH is required to
neutralise exactly 25.0 cm3 of 0.125 moldm-3 H2SO4 ?
6.25 cm3
50 cm3
12.5 cm3
25.0 cm3
Wrong Answer!
Conc x Vol of NaOH = 2 x Conc x Vol of H2SO4
0.25 x Vol of NaOH = 2 x 0.125 x 25
Vol of NaOH = 25 cm3
Question 8
Which expression represents the density of a gas
sample of relative molar mass, Mr, at
temperature T, and pressure, P?
PM r
RT
RM r
PT
RT
PM r
PM r
T
Wrong Answer!
nRT  PV
m
PV

M r RT
m PM r

V
RT
Density =
PM r
RT
Question 9
Separate samples of two gases, each containing a
pure substance, are found to have the same
density under the same conditions of
temperature and pressure. Which statement
about these two samples must be correct?
They have the same
volume.
There are equal numbers
of moles in the two
samples.
They have the same
relative molecular mass.
They condense at the
same temperature.
Wrong Answer!
nRT  PV
Under the same pressure and
temperature where R is a constant, they
should have the same relative molecular
mass.
m
PV

M r RT
m PM r

V
RT
Density =
PM r
RT
Question 10
A 250 cm3 sample of an unknown gas has a mass
of 1.42g at 350C and 0.85 atmospheres. Which
expression gives its molar mass, Mr? (R = 82.05
cm3 atm K-1 mol-1)
1.41 82.05  35
0.25  0.85
1.41 82.05  308
0.25  0.85
1.41 250  0.85
82.05  308
1.41 82.05  308
250  0.85
Wrong Answer!
nRT  PV
mass
RT  PV
Mr
Mr 
massRT
PV
Question 11
What is the concentration of nitrate ions in 0.500cm3
of 0.60moldm-3 Fe(NO3)3 solution?
0.60 moldm-3
0.90 moldm-3
1.20 moldm-3
1.80 moldm-3
Wrong Answer!
Fe(NO3)3  Fe3+(aq) + 3NO3-(aq)
Nitrate ions concentration = (0.6 x 3) = 1.80 moldm-3
Question 12
32.0 grams of sulfur (atomic mass of 32.0)
combine with a metal, M (atomic mass of 40.0)
to give a product which weighs 52.0g. What is
the empirical formula of the sulfide formed?
MS
MS2
M 2S
M2S5
Wrong Answer!
Amount of M atoms = (52-32)/40 = 0.50 mol
Amount of S atoms = 32/32 = 1.0 mol
Multiplying through by 2 gives MS2
Question 13
Under what conditions of temperature and pressure will a
real gas behave most like an ideal gas?
Temperature
Pressure
Low
Low
High
Low
High
High
Low
High
Wrong Answer!
High pressure will bring the gas molecules very close
together. This causes more collisions and also allows the
weaker attractive forces to operate. With low
temperatures, the gas molecules do not have enough
kinetic energy to continue on theire path to avoid the
attraction.
Question 14
At stp (i.e. 00C and 1 atm pressure (101 kPa)), it
was found that 1.15 dm3 of a gas weighed
3.96g. What is its molar mass?
77 gmol-1
47 gmol-1
39 gmol-1
4 gmol-1
Wrong Answer!
PV 101000 Pa 1.15 103 m3
n

 0.0512mol
1 1
RT
8.31Jmol K  273K
3.96g
Molar mass =
 77.34 gmol 1
0.0512mol
Question 15
A sample of argon gas in a sealed container of
fixed value is heated from 50 to 2500C. Which
quantity will remain constant?
Average speed of the
atoms
Pressure of the gas
Average kinetic
energy of the atoms
Density of the argon
Wrong Answer!
All properties will increase in value except density which
remain constant since the mass and volume of gas
remain constant.
Question 16
Nitrogen(II) oxide,NO, is made from the oxidation of NH3:
4NH3 + 5O2  4NO + 6H2O
An 8.5g sample of NH3 gives 15.0g of NO. What is the
percentage yield of NO?
40%
60%
80%
100%
Wrong Answer!
Amount of NH3 = 8.5/17 = 0.5 mol
Amount of NO = 15/30 = 0.5 mol
Percentage yield = 0.5/0.5 x 100% = 100%
Question 17
A pure compound contains 24g of carbon, 4g of
hydrogen and 32g of oxygen. No other elements
are present. What is the empirical formula of the
compound?
C2H4O2
CH2O
CH4O
CHO
Wrong Answer!
No. of moles of C = 24/12 = 2
No. of moles of H = 4/1 = 4
No. of moles of O = 32/16 = 2
Dividing all by 2 gives a ratio of C:H:O = 1:2:1
The empircal formula is CH2O
Question 18
1000cm3 of ammonia gas combines with 1250cm3 of
oxygen to produce two gaseous compounds with a
combined volume of 2500cm3, all volumes being
measured at 2000C and 0.500 atm pressure. Which of
the following equations fits the facts?
4NH3 + 7O2 
4NO2 + 6H2O
4NH3 + 5O2 
4NO + 6H2O
4NH3 + 5O2 
4N2O2 + 6H2O
4NH3 + 3O2 
2N2+ 6H2O
Wrong Answer!
4 vol + 5 vol  10 vol
Experimental data 1 vol + 1.25 vol  2.5 mol
Multiplying throughout by 4 gives 4 vol + 5 vol  10 vol
Question 19
Butane burns in oxygen according to the equation
2C4H10(g) + 13O2(g)  8CO2(g) + 10H2O(g)
If 11.6g of butane is burned in 11.6g of oxygen
which is the limiting reagent?
Neither
Butane
Oxygen
Oxygen and butane
Wrong Answer!
No. of moles of butane = 11.6/58 = 0.2
No. of moles of oxygen = 11.6/32 = 0.3625
2 mols of butane react with 13 mols of oxygen
0.2 mols of butane will react with 1.3 mols of oxygen.
0.3625 mols of oxygen will react with 0.05577 mols butane.
The limiting reagent is oxygen since the no. of mols of butane
produced by 0.3625 mols is smaller.
Question 20
A 350cm3 sample of helium gas is collected at
22.00C and 99.3kPa. What volume would this
gas occupy?
318cm3
450cm3
477cm3
220cm3
Wrong Answer!
350cm3  99.3kPa  273K
V2 
101.3kPa  295 K
V2  317.5034cm3  318cm3
Question 21
When 250 cm3 of 3.00 moldm-3 HCl(aq) is added
to 350 cm3 of 2.00 moldm-3 HCl(aq) the
concentration of the solution of hydrochloric acid
obtained in moldm-3 is:
1.45
2.90
2.50
2.42
Wrong Answer!
(250+350)/1000 x Conc of HCl
= 250/1000 x 3 + 350/1000 x 2
Conc of HCl = (0.25 x 3 + 0.35 x 2)/0.6 = 2.416moldm-3
Question 22
Magnesium reacts with hydrochloric acid according to the
following equation:
Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g)
What mass of hydrogen will be obtained if 100 cm3
of 2.00 moldm-3 HCl are added to 4.86g of magnesium?
2.0g
0.8g
0.4g
0.2g
Wrong Answer!
No. of moles of HCl = 100/1000 x 2 = 0.2
No. of moles of Mg = 4.86/24 = 0.2025
The limiting reagent is HCl
Since 2 mols of HCl produces 1 mol H2, 0.2 mols of HCl
produces 0.1 mol H2. Hence, 0.1 x 2g = 0.2g of H2
Question 23
12g of anhydrous magnesium sulfate combines
with 12.6g of water to form hydrated manesium
sulfate. What is the formula of the hydrated
magnesium sulfate?
MgSO4.9H2O
MgSO4.7H2O
MgSO4.5H2O
MgSO4.3H2O
Wrong Answer!
No. of moles of MgSO4 = 12/122 = 0.09836
No. of moles of H2O = 12.6/18 = 0.7
Multiplying by 10 to both gives approximately
1 mole MgSO4 and 7 moles H2O
Question 24
In order to dilute 40.0 cm3 of 0.600 moldm-3
HCl(aq) to 0.100 moldm-3, what volume of water
must be added?
60 cm3
160 cm3
200 cm3
240 cm3
Wrong Answer!
M1V1= M2V2
0.600moldm-3 x 40.0cm3 = 0.600moldm-3 x V2
V2 = 240cm3
V2 – V1 = 240 – 40 = 200 cm3
Congratulations!