Choose the correct answer for each question.

1. A solution of sodium sulphide, Na2S, contains 7.8 g dm-3. What is the concentration, in mol dm-3, of sodium ions?
   

   1.   ?    0.05
   2.   ?    0.10
   3.   ?    0.20
   4.   ?    1.00

2. If 8.7 g of potassium sulphate is dissolved in water and made up to 200 cm3, what is the concentration of the solution in mol dm-3?
   

   1.   ?    0.05
   2.   ?    0.20
   3.   ?    0.25
   4.   ?    0.50

3. On heating with soda lime. sodium ethanoate decomposes in accordance with the following equation.
   CH3COONa (s)     +     NaOH (s)     =     CH4 (g)     +     Na2 CO3 (s)
   If 8.2 g of sodium ethanoate produced 560 cm³ of methane (at s.t.p.). which one of the following is the percentage yield of the reaction;
   

   1.   ?    2.5
   2.   ?    4.0
   3.   ?    12.0
   4.   ?    25.0

4. What mass of iron(II) ammonium sulphate-6-water,Fe(NH4)2(SO4)3.6H2O, (relative molecular mass = 392) must be dissolved in water to produce 1 litre of a solution which is 0.05M with respect to Fe2+(aq)?
   

   1.   ?    2.80
   2.   ?    14.2
   3.   ?    19.6
   4.   ?    28.0

5. 0.0640 g of an unknown sulphate yielded 0.1165 g of barium sulphate when appropriately treated with barium chloride. Which one of the following is the percentage of sulphate in the unknown?
   

   1.   ?    75
   2.   ?    45
   3.   ?    30
   4.   ?    25

6. Equal masses of sulphur dioxide and sulphur trioxide are mixed. The mole fraction of sulphur trioxide will be
   (Relative atomic masses: O=16, S=32)
   

   1.   ?    0.22
   2.   ?    0.44
   3.   ?    0.50
   4.   ?    0.56
   5.   ?    0.80

7. Calculate the number of protons present in the nuclei of the atoms contained in 2.24 dm3 of oxygen gas, O2, (atomic number of oxygen is 8) at standard temperature and pressure, given that one mole of gas under these conditions occupies 22.4 dm3 and the value of the Avogadro constant L   =  6.0 x 1023 mol-1.
   It equals
   

   1.   ?    9.6 x 1023
   2.   ?    6.0 x 1022
   3.   ?    4.8 x 1023
   4.   ?    9.6 x 1024

8. If L is the Avogadro constant the number of ions in 17.43 g of solid K2SO4 (relative molecular mass 174.3) will be
   

   1.   ?    L/30
   2.   ?    L/10
   3.   ?    3L/10
   4.   ?    30L

9. Chemical analysis showed that a sample of a substance contained only carbon, hydrogen and nitrogen in the following amounts: carbon, 0.060 g; hydrogen, 0.025 g and nitrogen, 0.080 g. What is the empirical formula for this substance?
   

   1.   ?    CH2N2
   2.   ?    CH3N2
   3.   ?    CH4N2
   4.   ?    CH5N

10. Indicate the modern definition of the term mole.
    The mole is the amount of pure substance which
    

    1.   ?    has a mass equal to the formula weight in grammes
    2.   ?    contains exactely 6.023 x 1023 elementary units (atoms, molecules, .....)
    3.   ?    would occupy, if gaseous at 273 K and 1.013 x 105 Nm-2 (1 atmosphere pressure), 22.414 dm3
    4.   ?    has exactely the same number of elementary units (atoms, molecules, ....) as there are oxygen atoms in 0.016kg of oxygen
    5.   ?    contains as many elementary units (atoms, molecules, ....) as there are carbon atoms in 0.012 kg of carbon-12

11. 12.0 g of carbon-12 contains the same number of atoms as in
    

    1.   ?    2 g of helium, He
    2.   ?    48 g of sulphur dioxide, SO2
    3.   ?    one mole of atoms of iron, Fe
    4.   ?    one mole of molecules of sulphur, S8

12. In 11.0 g of a compound of phosphorus and sulphur, it is found that 4.8 g of sulphur is combined with the phosphorus.
    What is the formula of the phosphorus sulphide?
    

    1.   ?    P2S3
    2.   ?    P3S3
    3.   ?    P3S2
    4.   ?    P4S3

13. Tin(IV) iodide can be made according to the equation:
    Sn     +    2I₂     =    SnI₄
    In an experiment 11.9 g of tin reacted with excess iodine to form 25.1 g of tin(IV) iodide. What is the percentage yield?
    

    1.   ?    20%
    2.   ?    40%
    3.   ?    47%
    4.   ?    80%

14. Analysis of a compound containing sulphur and phosphorus showed that 4.40 g of the compound contained 2.48 g of phosphorus. What is the empirical formula of the compound?
    

    1.   ?    P₂S₃
    2.   ?    P₃S₂
    3.   ?    P₃S₄
    4.   ?    P₄S₃