Unit 1 – Amount of Substance (2009)
Q1-9 (Jan 2009), Q10 – 17 (Jun 2009)
Unit 1 - Jan 2009
Q1.
(a)  State the general formula of the alkanes, using the letter n to denote the number of carbon atoms in each molecule.
(1)

(b)  Alkanes are used as fuels. In the petrochemical industry, useful hydrocarbons are
       often produced from longer chain molecules.
       Name the type of reaction shown below.
(i)   
(1)
Type of reaction ....................................
(ii)   
(1)
Type of reaction ....................................
(c)  By what type of formula are the organic molecules in (b) represented?
(1)
........................................................................................................................................................................
(d)  Another reaction carried out in industry can be represented as shown below.

(i)   Give the molecular formula of compound 2.
(1)
........................................................................................................................................................................
(ii)   Give the name of compound 2.
(1)
............................................................................................................................................................................................................
(e)  An equation for the reaction between methane and chlorine is:

The reaction occurs in the presence of ultraviolet (UV) light via a free-radical chain mechanism.

 The initiation step is Cl2 → 2Cl

 The next step could be

(i)   Use the following data to calculate a value for the enthalpy change for each of the Steps, A and B.
(3)

Answer ....................................... kJ mol−1

Answer ....................................... kJ mol−1
(ii)   Use your answer to (i) to justify which of the Steps, A or B, is the more likely.
(1)
........................................................................................................................................................................
........................................................................................................................................................................
(f)  Another halogenoalkane, bromomethane, CH3Br, is a toxic gas used to protect plants against insects.

       Health and Safety advice states that concentrations above 5 parts per million (ppm) by volume of this gas are harmful.
       A research laboratory contains 2.5 × 105 dm3 of air.  Calculate the maximum volume of bromomethane, in dm3, allowed in the laboratory to comply with the advice given.
(1)

(Total for question = 11 marks)

Q2.
Which of the following contains the greatest number of hydrogen atoms?
   A     2 moles of water, H2O
   B     1.5 moles of ammonia, NH3
   C     1 mole of hydrogen gas, H2
   D     0.5 moles of methane, CH4
(Total for question = 1 mark)

Q3.
Magnesium oxide reacts with dilute hydrochloric acid according to the following equation.

How many moles of magnesium oxide, MgO, are required to neutralize 20 cm3 of 0.50 mol dm−3 hydrochloric acid, HCl?
   A     0.0010
   B     0.0050
   C     0.010
   D     0.020

(Total for question = 1 mark)
Q4.
 Hydrogen and oxygen react according to the following equation.

If all volumes are measured at 110 °C and one atmosphere pressure, the volume of steam produced after 50 cm3 of hydrogen react completely with 25 cm3 of oxygen is
   A     25 cm3
   B     50 cm3
   C     75 cm3
   D     100 cm3
(Total for question = 1 mark)

Q5.
An organic compound contains 38.4 % carbon, 4.80 % hydrogen and 56.8 % chlorine by mass.  What is the empirical formula of the compound?
   A     C2H3Cl
   B     CH3Cl
   C     C2H5Cl
   D     C3H5Cl3
(Total for question = 1 mark)

Q6.
 (a)  (i)   Complete the electronic configuration of the magnesium atom.
(1)
1s2
 ............................................................................................................................................. 
(ii)   Complete the electronic configuration of the chlorine atom.
(1)
1s2
 ............................................................................................................................................. 
(b)  (i)   Write the equation, including state symbols, for the reaction of magnesium with
              chlorine.
(2)

(ii)  Name the type of bonding present in magnesium chloride.
(1)
 ............................................................................................................................................. 
(iii)   Draw a diagram (using dots or crosses) to show the bonding in magnesium chloride.  Include ALL the electrons in each species and the charges present.
(3)

(c)  State the type of bonding that exists in solid magnesium.
(1)
Type
 ............................................................................................................................................. 
*(d)  Explain fully why the melting temperature of magnesium is higher than that of
         sodium.
(3)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
............................................................................................................................................. 
(Total for question = 12 marks)

Q7.
 Hydrogen peroxide decomposes on heating as follows:

What mass of hydrogen peroxide is required to give 16 g of oxygen gas?
   A     8.5 g
   B     17 g
   C     34 g
   D     68 g
(Total for question = 1 mark)

Q8.
 The equation for the dehydration of cyclohexanol, C6H11OH, to cyclohexene, C6H10 is:
C6H11OH → C6H10 + H2O
50.0 g of cyclohexanol produced 32.8 g of cyclohexene.
 [Molar masses / g mol−1 : cyclohexanol = 100; cyclohexene = 82]

 Calculate the percentage yield of cyclohexene.
   A     32.8 %
   B     40.0 %
   C     65.6 %
   D     80.0 %
(Total for question = 1 mark)

Q9.
 The standard enthalpy change, ΔH1 , for the decomposition of potassium hydrogencarbonate, KHCO3, is impossible to determine directly.

The value of ΔH1 can be calculated from the standard enthalpy changes which accompany the reactions below:

Procedure:

·	The solids were added to separate 30 cm3 portions of dilute hydrochloric acid.  The acid was in excess for both solids.
·	The maximum temperature change for each experiment was noted. 
Results:

·	The following results were obtained with KHCO3(s).

Mass of KHCO3 used = 2.00 g

Temperature change = −4.9 °C
·	The experiment with K2CO3(s) gave a ΔH3 value of −34 kJ mol−1.Assumption:

·	The dilute hydrochloric acid solution has a density of 1 g cm−3.

(a)  (i)   Calculate the heat energy absorbed, in joules, by the reaction of the KHCO3(s) with the solution of dilute hydrochloric acid.
Use the expression
energy absorbed (J)   =   mass of solution  ×  4.18  ×  temperature change
(1)

(ii)   Calculate the number of moles of KHCO3(s) used.  Assume that the molar mass of KHCO3(s) is 100 g mol−1.
(1)

(iii)   Use your answers to (a)(i) and (ii) to calculate, in kJ mol−1, the enthalpy change when one mole of KHCO3(s) reacts completely with the acid (i.e. ΔH2). Include a sign in your answer.
(2)

(b)  A Hess Cycle based on these reactions is shown below.

(i)   Apply Hess's Law to obtain an expression for ΔH1 in terms of ΔH2 and ΔH3
(1)
ΔH1=

(ii)   Use your answers to (a)(iii) and (b)(i), and the ΔH3 value of −34 kJ mol−1, to calculate a value for ΔH1 in kJ mol−1.  Include a sign in your answer.
(2)

(c)  The maximum errors for the apparatus used in the experiment with the KHCO3(s) were as follows:
Balance                       0.01g
Measuring cylinder      0.5 cm3
(i)   Calculate the maximum percentage error in using each of the following pieces of apparatus in the KHCO3(s) experiment:
(2)
Balance

Measuring cylinder

(ii)   Suggest a piece of apparatus that could have been used to measure the volume of dilute hydrochloric acid more accurately in this experiment.
(1)
      ..............................................................................................................................................
(Total for question = 10 marks)

Unit 1 - Jun 2009
Q10.
 Calculate the mass of calcium hydroxide, Ca(OH)2, present in 100 cm3 of a 0.100 mol dm−3 solution.
[Assume the molar mass of Ca(OH)2 is 74.0 g mol−1.]
   A     0.570 g
   B     0.740 g
   C       1.85 g
   D       3.70 g
(Total for question = 1 mark)

Q11.
 A compound was analysed and found to contain

[Relative atomic masses: C = 12; H = 1; N = 14]
The empirical formula of the compound is
   A     CH3N
   B     CH4N
   C     CH5N
   D     C2H4N
(Total for question = 1 mark)

Q12.
 Propanone, C3H6O, undergoes complete combustion to form carbon dioxide and water.

(a)  In an experiment to calculate the enthalpy change of combustion for propanone, 2.90 g of propanone was burned completely in oxygen.
       The heat energy from this combustion raised the temperature of 200 g of water from 20.2 °C to 78.4 °C.
       The specific heat capacity of water is 4.18 J g−1°C−1.
(i)  Calculate the number of moles of propanone present in 2.90 g.
[The molar mass of propanone is 58 g mol−1.]
(1)

(ii)  Use the expression

to calculate the heat energy transferred to raise the temperature of 200 g of water from 20.2 °C to 78.4 °C.
(2)

(iii)  Use your answers to (a)(i) and (ii) to calculate a value for the enthalpy change of combustion of propanone.  Give your answer to three significant figures and include a sign and units.
(3)

(b)  In another experiment, the enthalpy change of combustion for butanone, C4H8O, was found to be −1300 kJ mol−1.
        A Data Book value for the standard enthalpy change of combustion for butanone is −2440 kJ mol−1.
(i)  Suggest a reason why the value obtained in the experiment is so different from the Data Book value.
(1)
 ............................................................................................................................................. 
(ii)  This Data Book value (−2440 kJ mol−1) refers to the following equation.

How would the value be different if it referred to the formation of water in the gaseous state?  Justify your answer.
(2)
Difference
 ............................................................................................................................................. 
Justification
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(c)  Standard enthalpy changes of combustion can be used to calculate the standard enthalpy change of formation of a compound.
(i)  Define the term standard enthalpy change of formation, making clear the meaning of standard in this context.
(3)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (ii)  Use the standard enthalpy changes of combustion, ΔHc, given in the table below to find the standard enthalpy change of formation for ethanoic acid, CH3COOH, in kJ mol−1.

(3)

(Total for question = 15 marks)

Q13.
This question is about hydrocarbons.
(a)  Liquefied petroleum gas (LPG) is a fuel sold as an alternative to petrol.  It is a mixture of liquefied C3 and C4 alkanes.
(i)  Suggest a reason why the alkanes are liquefied.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(ii)  There are two C4 alkanes. Draw skeletal formulae of each of the C4 alkanes in the spaces provided.
       Name each alkane.
(4)

(iii)  Complete the following sentence.
(1)
Compounds with the same molecular formula but different structural formula

 are called .........................................

(b)  Propane, C3H8, reacts with chlorine, Cl2, in a substitution reaction.

The mechanism for this reaction is described in three stages.
(i)  Give the initiation step for this reaction and state the condition necessary for this step to occur.
(2)
Initiation step

Condition
 ............................................................................................................................................. 

(ii)  Give the TWO propagation steps for this reaction.
(2)

(iii)  Give a possible termination step for this reaction.
(1)

(c)  Myrcene, C10H16, is a naturally occurring compound which is used in perfumes.

(i)  Name the functional group in myrcene.
(1)
 ............................................................................................................................................. 
(ii)  What colour change would you observe when bromine, dissolved in an organic
        solvent, is added to myrcene?
(1)
From .............................................................................. To 

........................................................................................................
(iii)  Classify the type and mechanism of the reaction that occurs when myrcene reacts with bromine, Br2.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 

(iv)  In an experiment, 1.36 g of myrcene (molar mass: 136 g mol−1) was found to react with 0.72 dm3 of hydrogen, H2, in the presence of a nickel catalyst.

        Use this information to draw the structural formula of the product of the reaction between myrcene and hydrogen.

        [Assume the molar volume of H2 under the conditions of the experiment is 24 dm3mol−1.]
(2)
Calculation

Hence structural formula of the product

(d)  Myrcene is one of a group of compounds related to 2-methylbut-2-ene shown below.

2-methylbut-2-ene undergoes addition polymerization in a similar way to ethene.

 Draw the structural formula of the repeat unit of the polymer formed.
(2)

(Total for question = 19 marks)

Q14.
The graph shows the variation in melting temperatures of the elements across Period 3 (Na to Ar) of the Periodic Table.

(a)  Complete the table below to show the type of structure and bonding for the elements
       shown.
(3)

(b)  Explain why silicon has a much higher melting temperature than sulfur.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
*(c)  Explain why the melting temperature increases from sodium to aluminium.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (d)  Magnesium forms the basic oxide magnesium oxide, MgO.  This oxide is almost
        insoluble in water.  On gentle warming with dilute sulfuric acid, magnesium oxide
        reacts to form aqueous magnesium sulfate solution.
*(i)  Describe how you would use the above reaction to prepare a pure sample of
        magnesium sulfate.
(5)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
............................................................................................................................................. 
(ii)  Suggest what action should be taken if a pupil spilt a small quantity of dilute
       sulfuric acid on a laboratory bench.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 

 (e)  The data in the table below will be useful when answering this question.

Magnesium carbonate reacts with dilute sulfuric acid.

(i)  Explain why the reaction between strontium carbonate and dilute sulfuric acid stops after a few seconds.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (ii)  Strontium sulfate is produced when aqueous sodium sulfate is added to aqueous strontium chloride.
       Give the ionic equation for the reaction, including state symbols.
(2)

(Total for question = 16 marks)

Q15.
Which of the following gas samples occupies the greatest volume at the same temperature and pressure?

   A     1 gram of ethane
   B     1 gram of oxygen
   C     1 gram of fluorine
   D     1 gram of neon
(Total for question = 1 mark)

Q16.
 17.1 g of aluminium sulfate, Al2(SO4)3, was dissolved in water.
Calculate the number of sulfate ions, SO42−, present in the solution formed.
[Assume the molar mass of Al2(SO4)3 is 342 g mol−1 and the Avogadro Constant is 6 × 1023 mol−1.]
   A     3 × 1021
   B     1 × 1022
   C     3 × 1022
   D     9 × 1022
(Total for question = 1 mark)

Q17.
 Sodium hydrogensulfate, NaHSO4, reacts with sodium hydroxide, NaOH, as shown below.

0.0100 mol of sodium hydrogensulfate is neutralized with dilute sodium hydroxide, concentration 0.200 mol dm−3.
Calculate the volume of sodium hydroxide required.
   A     20.0 cm3
   B     50.0 cm3
   C     100 cm3
   D     500 cm3
(Total for question = 1 mark)