Science

• Pencils may be used for any diagrams, graphs or rough working.
• Staples, paper clips, highlighters, glue or correction fluid must not be used in the examination.
• Barcodes should not be written in the examination.
• All questions must be answered in the examination.
• A copy of the Periodic Table is printed on page 16 of the examination paper.
• At the end of the examination, all work should be fastened securely together.
• The number of marks is given in brackets [ ] at the end of each question or part question.
• The examination is paper 3 (Extended) of the International General Certificate of Secondary Education in Chemistry, with a duration of 1 hour 15 minutes.
• No additional materials are required for the examination.
• The examination consists of 14 printed pages and 2 blank pages.
• The examination paper includes information about six substances, their melting points, boiling points, electrical conductivities as solids and liquids, and whether they could have a macromolecular structure similar to that of silicon( IV ) oxide.
• Chromium is used to electroplate steel objects.
• Zinc blende, ZnS, is an ore of the important metal zinc and is changed into zinc oxide which is then reduced to the impure metal by carbon reduction.
• Chromium is a transition element.
• The experiment was repeated but 1.0 g of manganese( IV ) oxide was added.
• To 50 cm3 of aqueous hydrogen peroxide, 0.50 g of manganese( IV ) oxide was added.
• Chromium is added to the lead anode and the object to be plated is dipped in chromium( III ) sulfate(aq).
• The average reaction rate was calculated for each 20 second interval.
• More chromium( III ) sulfate(aq) is added to the plating solution.
• The decomposition of hydrogen peroxide is catalysed by manganese( IV ) oxide.
• Steel objects are plated with chromium to prevent corrosion.
• The name of the colourless gas formed at the positive electrode (anode) is unknown.
• The equation for the reaction at the negative electrode (cathode) is Cr(OH)2 + SO4 2- → Cr(SO4)2 + H2O.
• The volume of oxygen formed was measured every 20 seconds.
• The diagram shows how steel objects are plated with chromium.
• The formula of the chromium( III ) ion is Cr 3+ and of the sulfate ion is SO 4 2–.
• A colourless gas, which relights a glowing splint, is formed at the positive electrode (anode).
• Zinc oxide is obtained from zinc sulfide by heating.
• Sulfurous acid needs to react with water to form sulfuric acid.
• Heat mineral wool soaked in butan-1-ol can oxidise butan-1-ol to liquid X whose pH is 4, formed by oxidation of butan-1-ol.
• Another reagent which can oxidise butan-1-ol is hydrogen peroxide.
• Sulfuric acid is a strong acid.
• Sulfur dioxide is used in the manufacture of wood pulp.
• Sulfur dioxide is manufactured by reacting sulfur with oxygen.
• The major use of sulfur dioxide is to manufacture sulfuric acid.
• The formula of liquid X is C2H5O2.
• Ethanol can be made by fermentation, where yeast is added to aqueous glucose, resulting in the formation of carbon dioxide and the mixture becoming warm due to the exothermic reaction.
• The rate of reaction increases initially due to the formation of a surface layer of butan-1-ol, which slows down the reaction.
• Given solutions of both acids, how could you show that sulfuric acid is a strong acid and ethanedioic acid is a weak acid?
• Sulfur dioxide is also used as the food additive E220 to preserve food.