Question 6

6.1 Potassium permanganate, KMnO4, burns with a bright flame when a few drops of glycerine are added to it.

The incomplete equation for the reaction is:

6.1.1 Define the term molar mass. (2)

6.1.2 The composition of glycerine is as follows: 39,13% carbon; 8,7% hydrogen; 52,17% oxygen Determine the EMPIRICAL formula of glycerine. Show ALL calculations. (6)

6.1.3 Write down the value of x in the equation above if the MOLECULAR formula of glycerine is C3H8O3. (1)

6.1.4 Calculate the mass of Mn2O3 that can be prepared if 18 g of KMnO4 reacts with excess glycerine. (4)

6.2 The balanced equation for the reaction of sodium chloride, NaCℓ, with sulphuric acid, H2SO4, is as follows:

During a reaction, 1,5 g of an impure sample of sodium chloride reacts with 100 cm3 sulphuric acid of concentration 0,1 mol·dm-3 at room temperature.

6.2.1 Define the term concentration. (2)

6.2.2 Calculate the number of moles of sulphuric acid used in the reaction above. (3)

On completion of the reaction it is found that 460 cm3 of HCℓ gas has formed

6.2.3 Calculate the percentage purity of the sodium chloride. Use 24,45 dm3 as the molar gas volume (Vm) at room temperature. (6)


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