Quantitative Chemistry

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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?

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Wrong Answer!
Molar mass of CH3COOH is 24 4 32 60
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Question 2

• Which is not a true statement?

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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.
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Question 3

• Which sample has the greatest mass?

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Wrong Answer!
A 1 x (284) 32g B 2 x 28 56g C 3 x (143)
51g D 25 x 2 50g
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Question 4

• Which one of the following statements about SO2
  is/are correct?
• One mole of SO2 contains 1.8 x 1024 atoms
• One mole of SO2 has a mass of 64g

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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.
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Question 5

• 2Cl2 represents

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Wrong Answer!
2Cl2 represents two chlorine molecules Cl-Cl
and Cl-Cl
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Question 6

• Which one of the following equations is not
  correctly balanced?

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Wrong Answer!
The charge is not balanced.
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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 ?

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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
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Question 8

• Which expression represents the density of a gas
  sample of relative molar mass, Mr, at temperature
  T, and pressure, P?

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Wrong Answer!
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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?

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Wrong Answer!
Under the same pressure and temperature where R
is a constant, they should have the same relative
molecular mass.
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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)

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Wrong Answer!
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Question 11

• What is the concentration of nitrate ions in
  0.500cm3 of 0.60moldm-3 Fe(NO3)3 solution?

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Wrong Answer!
Fe(NO3)3 ? Fe3(aq) 3NO3-(aq) Nitrate ions
concentration (0.6 x 3) 1.80 moldm-3
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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?

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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
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Question 13

• Under what conditions of temperature and pressure
  will a real gas behave most like an ideal gas?
• Temperature Pressure

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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
their path to avoid the attraction.
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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?

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Wrong Answer!

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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?

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Wrong Answer!
All properties will increase in value except
density which remain constant since the mass and
volume of gas remain constant.
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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?

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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
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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?

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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 CHO 121 The
empircal formula is CH2O
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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?

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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
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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?

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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.
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Question 20

• A 350cm3 sample of helium gas is collected at
  22.00C and 99.3kPa. What volume would this gas
  occupy?

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Wrong Answer!
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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

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Wrong Answer!
(250350)/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
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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?

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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
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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?

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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
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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?

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Wrong Answer!
M1V1 M2V2 0.600moldm-3 x 40.0cm3 0.600moldm-3
x V2 V2 240cm3 V2 V1 240 40 200 cm3
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Congratulations!