Question 5
- (i) Describe briefly how trioxonitrate (v) ions could be tested for in the laboratory.
(ii) State two uses of each of the following compounds:
I. sodium chloride;
II. sodium trioxocarbonate (IV). [7 marks] - (i) Write balanced equations for the reaction involved in the extraction of iron in the blast furnace.
(ii) State Faraday’s first law of electrolysis.
(iii) State two applications of electrolysis. [ 9 mark] - Concentrated tetraoxosulphate (VI) acid is added to sugar crystals in a beaker.
State what would be observed. Explain briefly your answer - Write an equation for the reaction of zinc powder with:
(i) dilute tetraoxosulphate (VI) acid;
(ii) concentrated tetraoxosulphate (VI) acid. - What property of concentrated tetraoxosulphate (VI) acid is shown in 5(d)(ii)?
Observation
The question was popular, and majority of the candidates responded to it.
In part (a), majority of the candidates could not describe how trioxonitrate (V) ions could be tested in the laboratory. However, majority of the candidates stated correctly two uses of NaCl and Na2CO3.
In part (b), majority of the candidates could not completely write balanced equations for the reaction involved in the extraction of iron in the blast furnace. Majority of them left out the two equations for the removal of earthy impurities. In addition, majority of the candidates stated the Faraday’s first law of electrolysis.
In part (c), majority of the candidates could not state correctly what would be observed when concentrated tetraoxosulphate (VI) acid is added to sugar crystals in a beaker.
In part (d), majority of the candidates could write the equation for the reaction of zinc powder with dilute tetraoxosulphate (VI) acid, but could not write the equation for the reaction of zinc with concentrated tetraoxosulphate (VI) acid.
In part (e), majority of the candidates could not state the property of concentrated tetraoxosulphate (VI) nin the reaction between zinc powder and concentrated tetraoxosulphate (VI) acid.
The expected answers include:
-
(i) To the test solution, add freshly prepared iron (II) tetraoxosulphate(VI) (FeSO4) solution and followed by Conc. H2SO4. A brown ring is observed.
OR
(ii) I. Uses of sodium chloride
- food seasoning
- food preservative
- glazing pottery / earthen ware
- soap production
- crude oil refining
- water softener
- production of chlorine/hydrogen / sodium metal / NaOH / NaClO3 / NaOCl / Na2CO3
- lowering melting point of ice / preparation of freezing mixture
- used in tannery industry / tanning
II. Uses of sodium trioxocarbonate (IV)
- manufacture of glass / borax
- in detergents / soap
- manufacture of paper
- softening hardwater
- manufacture of NaOH
- treating (concentrated ) acid splash
- standardization of acids / analytical reagent -
(ii) It states that the mass of an element discharged at the electrode is directly proportional to the quantity of electricity passed.
(iii) - electroplating of metals
- extraction of metals
- purification of metals
- preparation of compounds / elements -
Beaker becomes warm formation of black solid
- The concentrated acid dehydrates the sugar
- A mass of carbon / black soot / sugar charcoal is formed
- Reaction is exothermic -
- Oxidizing