Unit 1 – Amount of Substance (2011)
Q1-9 (Jan 2011), Q10 – 17 (Jun 2011)
Unit 1 - Jan 2011
Q1.
 The Avogadro constant is 6.0 x 103 mol−1. Therefore the number of atoms in 1 mol of carbon dioxide is
   A      2.0 x 1023
   B      6.0 x 1023
   C      1.2 x 1024
   D      1.8 x 1024
(Total for question = 1 mark)

Q2.
 The compound butane has
   A      the empirical formula C4H10 and the molecular formula C2H5.
   B      the empirical formula C2H5 and the molecular formula C4H10.
   C      the empirical formula C2H5 and the molecular formula CnH2n+2.
   D      the empirical formula CnH2n+2 and the molecular formula C4H10.
(Total for question = 1 mark)

Q3.
 This question is about the element chlorine (atomic number = 17).
(a) Complete the electronic structure of chlorine.
(1)
1s2 2s2
 ............................................................................................................................................. 
(b) Chlorine forms compounds with magnesium and with carbon.
(i) Draw a dot and cross diagram to show the electronic structure of the compound magnesium chloride (only the outer electrons need be shown). Include the charges present.
(2)

(ii) Draw a dot and cross diagram to show the electronic structure of the compound tetrachloromethane (only the outer electrons need be shown).
(2)

*(iii) Suggest why the melting temperature of magnesium oxide is higher than that of magnesium chloride, even though both are almost 100% ionic.
(3)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (c) Magnesium chloride may be prepared from magnesium by reaction with chlorine or with hydrochloric acid. Compare these two preparations in terms of the atom economies of the reactions. No calculation is required.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (Total for question = 10 marks)

Q4.
 The equation for the complete combustion of octane is

(a) The mass of 10 mol of octane is
(1)
   A      0.66 kg 
   B      1.14 kg 
   C      2.10 kg 
   D      2.28 kg 

(b) The volume of 1 mol of any gas (measured at room temperature and pressure) is 24 dm3. Hence the volume of oxygen (measured at room temperature and pressure) required for the complete combustion of 10 mol of octane is
(1)
   A      240 dm3
   B      300 dm3
   C      3000 dm3
   D      6000 dm3
(Total for question = 2 marks)

Q5.
 (a) Coral reefs are produced by living organisms and predominantly made up of calcium carbonate. It has been suggested that coral reefs will be damaged by global warming because of the increased acidity of the oceans due to higher concentrations of carbon dioxide.
(i) Write a chemical equation to show how the presence of carbon dioxide in water results in the formation of carbonic acid. State symbols are not required
(1)

(ii) Write the ionic equation to show how acids react with carbonates. State symbols are not required.
(2)

(b) One method of determining the proportion of calcium carbonate in a coral is to dissolve a known mass of the coral in excess acid and measure the volume of carbon dioxide formed.
      In such an experiment, 1.13 g of coral was dissolved in 25 cm3 of hydrochloric acid (an excess) in a conical flask. When the reaction was complete, 224 cm3 of carbon dioxide had been collected over water using a 250 cm3 measuring cylinder.
(i) Draw a labelled diagram of the apparatus that could be used to carry out this experiment.
(2)

(ii) Suggest how you would mix the acid and the coral to ensure that no carbon dioxide escaped from the apparatus.
(1)
 ............................................................................................................................................. 
 (iii) Calculate the number of moles of carbon dioxide collected in the experiment.
  [The molar volume of any gas is 24 000 cm3 mol−1 at room temperature and pressure.]
(1)

(iv) Complete the equation below for the reaction between calcium carbonate and hydrochloric acid by inserting the missing state symbols.
(1)
CaCO3(..............) + 2HCl(..............) → CaCl2(..............) + H2O(l) + CO2(..............)
(v) Calculate the mass of 1 mol of calcium carbonate.
      [Assume relative atomic masses: Ca = 40, C = 12, O = 16.]
(1)

(vi) Use your data and the equation in (iv) to calculate the mass of calcium carbonate in the sample and the percentage by mass of calcium carbonate in the coral. Give your final answer to three significant figures.
(2)

(vii) When this experiment is repeated, the results are inconsistent. Suggest a reason for this other than errors in the procedure, measurements or calculations.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(Total for question = 12 marks)

Q6.
 The enthalpy change of combustion of ethanol was determined using the apparatus shown in the diagram below. In the experiment, the temperature increase of the water in the beaker is measured when a known mass of the ethanol is burned.

(a) The results of the experiment are summarised in the table below.

(i) Calculate the heat energy produced by the combustion of the alcohol using the equation.
                  heat energy produced (J) = mass of water x 4.18 x temperature change
(1)

(ii) Calculate the number of moles of ethanol burned in this experiment (the formula of ethanol is C2H5OH).
(3)

(iii) Use the equation below to calculate the enthalpy change of combustion of ethanol in kJ mol−1. Give the value an appropriate sign.
ΔH = heat energy produced ÷ number of moles
(2)

(b) The data book value for the enthalpy change of combustion of ethanol is −1370 kJ mol−1.
(i) Calculate the percentage error in the value calculated in (a)(iii) in comparison with the data book value.
(1)

(ii) List three ways in which the design of the experiment causes the results to be so different from the data book value. (You should be specific but detailed explanations are not required.)
(3)
1
 ............................................................................................................................................. 
2
 ............................................................................................................................................. 
3
 ............................................................................................................................................. 
 (iii) Use the data book values for enthalpy changes of combustion given in the table below to calculate the enthalpy change of formation of ethanol.
(3)

(Total for question = 13 marks)
Q7.
 For the oxidation of ammonia

the values of the coefficients in the balanced equation are
   A      a = 2, b = 3, c = 2 and d = 3
   B      a = 4, b = 7, c = 4 and d = 4
   C      a = 4, b = 5, c = 4 and d = 6
   D      a = 6, b = 7, c = 6 and d = 9
(Total for question = 1 mark)

Q8.
 In 2006, the concentration of carbon dioxide in the atmosphere was 382 ppm. This is equivalent to
   A     0.00382%
   B     0.0382%
   C     0.382%
   D     3.82%
(Total for question = 1 mark)

Q9.
Most compounds of lead are insoluble, an exception being lead(II) nitrate. Therefore a good method of preparing lead(II) sulfate is
   A     adding dilute sulfuric acid to lead metal.
   B     adding concentrated sulfuric acid to lead metal.
   C     adding dilute sulfuric acid to lead(II) nitrate solution.
   D     adding dilute sulfuric acid to solid lead(II) oxide.
(Total for question = 1 mark)

Unit 1 - Jun 2011
Q10.
For drivers in the UK, the legal limit of the concentration of ethanol (molar mass 46 g mol−1) in the blood is 80 mg per 100 cm3. This is equivalent to a concentration of
   A    17.4 mol dm−3
   B    1.74 mol dm−3
   C    0.0174 mol dm−3
   D    0.00174 mol dm−3
(Total for Question = 1 mark)
Q11.
 This question is about alkanes.
(a) The skeletal formulae of two alkanes (A and B) are shown below.

      (i)   Write the general formula of the alkanes.
(1)

      (ii)  Compounds A and B are ................................................... of each other.
(1)
      (iii)  Draw the displayed formula of compound A.
(1)

      (iv)  Give the systematic name of compound B.
(1)
 ............................................................................................................................................. 

(b) The largest use for alkanes is as fuels. However, there are problems associated with the combustion of alkanes, whether complete or incomplete.
      (i)   An incomplete combustion of methane, CH4, results in the formation of carbon monoxide and water only.
Write the equation for this reaction. State symbols are not required.
(2)

      (ii)  When does incomplete combustion occur?
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
      (iii)  State two problems that result from the incomplete combustion of alkane fuels.
(2)
1 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
2 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
    ∗(iv)  State and explain the main environmental problem arising from the complete combustion of alkane fuels.
(3)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (c) The reactions of organic compounds, including alkanes, may be broken down into a series of steps; this is the mechanism for the reaction. The reaction between methane and chlorine may be represented by a mechanism involving three stages - initiation, propagation and termination.
      (i)   Reaction mechanisms often involve the use of 'curly arrows'. Explain the meaning of the curly arrows shown below.
(2)

Arrow I
 ............................................................................................................................................. 
 ............................................................................................................................................. 
Arrow II
 ............................................................................................................................................. 
 ............................................................................................................................................. 
      (ii)  Using the curly arrow notation, show the initiation step of the reaction between methane and chlorine.
(2)

      (iii)  Give the two propagation steps of the reaction between methane and chlorine.
              Curly arrows are not required.
(2)

      (iv)  Suggest why a small amount of UV light can result in the formation of a large amount of product.
(1)
 ............................................................................................................................................. 
      (v)   Ethane is a trace product of this reaction. By means of an equation, show how the ethane is formed.
(1)

(d) Scientists never detect molecular hydrogen, H2, amongst the products of the chlorination of methane.
Use the data below to suggest why this is so.
The frequency of UV light used corresponds to an energy of about 400 kJ mol−1.

(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (Total for Question = 22 marks)

Q12.
 An important reaction which occurs in the catalytic converter of a car is

In this reaction, when 500 cm3 of CO reacts with 500 cm3 of NO at 650 °C (the operating temperature of the catalyst) and at 1 atm, the total volume of gases produced at the same temperature and pressure is
   A    500 cm3
   B    750 cm3
   C    1000 cm3
   D    impossible to calculate without knowing the molar volume of gases under these conditions.
(Total for Question = 1 mark)

Q13.
 The elements in Group 1 of the Periodic Table have very similar chemical properties. This is because
   A    they have the same number of outer electrons.
   B    they have the same number of filled shells of electrons.
   C    their outer electrons are in the s sub-shell.
   D    their outer electrons have very similar shielding.
(Total for Question = 1 mark)

Q14.
0.400 g of magnesium ribbon reacted with exactly 22.2 cm3 of hydrochloric acid of concentration 1.50 mol dm−3.
400 cm3 of hydrogen gas was formed, the volume being measured at room temperature
 and pressure.
In the calculations that follow, use the following molar masses:
Mg = 24.0 g mol−1
Cl = 35.5 g mol−1
(a) Calculate the amount (in moles) of magnesium used.
(1)

(b) Calculate the amount (in moles) of hydrochloric acid used.
(1)

(c) Calculate the amount (in moles) of hydrogen produced.
      [Molar volume of any gas at room temperature and pressure = 24 000 cm3 mol−1]
(1)

(d) Show that the calculated amounts of magnesium, hydrochloric acid and hydrogen are consistent with the following equation for the reaction

(1)

(e) Calculate the maximum mass of magnesium chloride that would be formed in this reaction. Give your answer to three significant figures.
(3)

(Total for Question = 7 marks)

Q15.
 In the following outline of the Periodic Table, the letters A to D are not the symbols of the elements.

Select from A to D the element which
(a) is a non-metal with a high melting temperature and boiling temperature.
(1)
   A  
   B  
   C  
   D  

(b) is in the d block of the Periodic Table.
(1)
   A  
   B  
   C  
   D  

(c) has a very stable electronic structure.
(1)
   A  
   B  
   C  
   D  

(d) is a metal with a high melting temperature and boiling temperature.
(1)
   A  
   B  
   C  
   D  
(Total for Question = 4 marks)

Q16.
 The European Union has set a limit (with effect from January 2010) of 3.13 ppm for the proportion of the toxic gas carbon monoxide in the air that we breathe. This is equivalent to
   A    3.13%
   B    0.0313%
   C    0.000313%
   D    0.00000313%
(Total for Question = 1 mark)

Q17.
 Ethanol (molar mass 46 g mol−1) is manufactured by the hydration of ethene (molar mass 28 g mol−1):

In a typical process 28 tonnes of ethene produces 43.7 tonnes of ethanol. The percentage yield of ethanol in this process is
   A    64%
   B    95%
   C    100%
   D    156%
(Total for Question = 1 mark)