6.3. Reversible reactions and equilibrium
A subsection of Chemistry, 0620, through 6. Chemical reactions
Listing 10 of 390 questions
An atom of sulfur is represented by the symbol shown. 34S Describe this atom of sulfur in terms of: ● the position of the electrons, neutrons and protons in the atom ● the number of neutrons and number of protons ● the electronic configuration. Sulfur burns to produce sulfur dioxide. State one adverse effect of sulfur dioxide in the air. Complete the symbol equation for the reaction of sulfur dioxide with magnesium. + 2Mg → MgO + S shows the displayed formula of a compound of sulfur. F S O O O S O O F Deduce the molecular formula of this compound. Another compound of sulfur has the formula Na2S2O7. Complete Table 5.1 to calculate the relative formula mass of Na2S2O7. Table 5.1 type of atom number of atoms relative atomic mass sodium 2 × 23 = 46 sulfur oxygen relative formula mass = , ,
0620_s24_qp_32
THEORY
2024
Paper 3, Variant 2
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The major use of sulfur dioxide is to manufacture sulfuric acid. Another use of sulfur dioxide is as the food additive E220. How does it preserve food? Why is sulfur dioxide used in the manufacture of wood pulp? How is sulfur dioxide manufactured? Complete the following description of the manufacture of sulfuric acid. Sulfur dioxide reacts with to form sulfur trioxide. The above reaction is catalysed by . The optimum temperature for this reaction is °C. Sulfur trioxide needs to react with to form sulfuric acid. Defi ne the term acid. Sulfuric acid is a strong acid. Ethanedioic acid is a weak acid. Given solutions of both acids, how could you show that sulfuric acid is a strong acid and ethanedioic acid is a weak acid? method result for each acid 20.0 cm3 of sulfuric acid, concentration 0.30 mol / dm3, was added to 40 cm3 of sodium hydroxide, concentration 0.20 mol / dm3. 2NaOH + H2SO4 → Na2SO4 + 2H2O How many moles of H2SO4 were added? How many moles of NaOH were used? Which reagent is in excess? Give a reason for your choice. reagent in excess reason Is the pH of the fi nal mixture less than 7, equal to 7 or more than 7?
0620_w10_qp_32
THEORY
2010
Paper 3, Variant 2
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Sulfur is needed for the production of sulfuric acid. Two of the major sources of sulfur are ● underground deposits of the element sulfur, ● sulfur compounds from natural gas and petroleum. Explain why sulfur and its compounds are removed from these fuels before they are burned. Sulfur dioxide is made by spraying molten sulfur into air. The sulfur ignites and sulfur dioxide is formed. Suggest why molten sulfur is used in the form of a fi ne spray. Explain why traces of sulfur dioxide act as a preservative in fruit juices. State another use of sulfur dioxide. Describe how sulfur dioxide is changed into sulfur trioxide. Give the reaction conditions and an equation. Complete the following equations for the formation of sulfuric acid from sulfur trioxide. SO3 + → H2S2O7 H2S2O7 + ………. → H2SO4
0620_w11_qp_32
THEORY
2011
Paper 3, Variant 2
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The diagram shows one molecule of sulfur. S S S S S S S S How many atoms are there in three molecules of sulfur? Calculate the relative molecular mass of sulfur. Explain how acid rain is formed when fossil fuels containing sulfur are burnt. In your answer, include ● the name of a fossil fuel which contains sulfur, ● the gas formed when sulfur burns, ● the reactions which lead to the formation of acid rain. Potassium sulfate can be used as a fertiliser. The potassium in this fertiliser is an important element for plant growth. Name two other elements, important for plant growth, which are present in most fertilisers. and Describe a test for sulfate ions. test result
0620_w12_qp_21
THEORY
2012
Paper 2, Variant 1
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The food additive E220 is sulfur dioxide. It is a preservative for a variety of foods and drinks. State two other uses of sulfur dioxide. How is sulfur dioxide manufactured? Sulfur dioxide is a reductant (reducing agent). Describe what you would see when aqueous sulfur dioxide is added to acidifi ed potassium manganate(. Sulfur dioxide can also be made by the reaction between a sulfi te and an acid. Na2SO3 + 2HCl → 2NaCl + SO2 + H2O Excess hydrochloric acid was added to 3.15 g of sodium sulfi te. Calculate the maximum volume, measured at r.t.p., of sulfur dioxide which could be formed. The mass of one mole of Na2SO3 is 126 g.
0620_w12_qp_32
THEORY
2012
Paper 3, Variant 2
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Sulfur burns in air to form sulfur dioxide. Is sulfur dioxide an acidic or basic oxide? Give a reason for your answer. Sulfur dioxide is an atmospheric pollutant. Explain why sulfur dioxide in the atmosphere can erode buildings made of limestone. Sulfur dioxide reacts with oxygen to form sulfur trioxide. Sulfur trioxide can be made in the laboratory using the apparatus shown below. Sulfur trioxide has a melting point of 17 °C and a boiling point of 45 °C. ice sulfur trioxide crystals sulfur dioxide oxygen platinum catalyst concentrated sulfuric acid Suggest one safety precaution when carrying out this experiment. What is the purpose of the platinum catalyst? Complete the symbol equation for the reaction. 2SO2 + → SO3 Suggest why the sulfur trioxide is collected in a fl ask surrounded by ice. When 64 g of sulfur dioxide react with excess oxygen, 80 g of sulfur trioxide is formed. Calculate the mass of sulfur trioxide formed from 160 g of sulfur dioxide. mass = g Sulfur trioxide reacts with water to form sulfuric acid. A student used the apparatus shown below to determine the concentration of a solution of sodium hydroxide. sulfuric acid sodium hydroxide + indicator Which one of these pieces of apparatus should the student use to put 25.0 cm3 of sodium hydroxide into the fl ask. Tick one box. beaker measuring cylinder test-tube volumetric pipette How would the student know when the sulfuric acid had neutralised the sodium hydroxide? Clean air contains mainly nitrogen, noble gases, oxygen and water vapour. A teacher left a beaker of concentrated sulfuric acid open to the air for a week. After a week, the concentration of sulfuric acid in the beaker had decreased. at the start after one week concentrated sulfuric acid Explain these results by referring to one or more of the substances present in the air.
0620_w14_qp_23
THEORY
2014
Paper 2, Variant 3
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The main use of sulfur dioxide is the manufacture of sulfuric acid. State two other uses of sulfur dioxide. One source of sulfur dioxide is burning sulfur in air. Describe how sulfur dioxide can be made from the ore zinc sulfi de. The Contact process changes sulfur dioxide into sulfur trioxide. 2SO2+ O22SO3the forward reaction is exothermic temperature 400 to 450 °C low pressure 1 to 10 atmospheres catalyst vanadium(oxide What is the formula of vanadium(oxide? Vanadium(oxide is an effi cient catalyst at any temperature in the range 400 to 450 °C. Scientists are looking for an alternative catalyst which is effi cient at 300 °C. What would be the advantage of using a lower temperature? The process does not use a high pressure because of the extra expense. Suggest two advantages of using a high pressure? Explain your suggestions. Sulfuric acid is made by dissolving sulfur trioxide in concentrated sulfuric acid to form oleum. Water is reacted with oleum to form more sulfuric acid. Why is sulfur trioxide not reacted directly with water?
0620_w14_qp_31
THEORY
2014
Paper 3, Variant 1
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Sulfuric acid is an important acid, both in the laboratory and in industry. Sulfuric acid is manufactured in the Contact Process. Originally, it was made by heating metal sulfates and by burning a mixture of sulfur and potassium nitrate. Give a major use of sulfuric acid. A group of naturally occurring minerals have the formula of the type FeSO4.xH2O where x is 1, 4, 5, 6 or 7. The most common of these minerals is iron(sulfate-7-water. When this mineral is heated gently it dehydrates. FeSO4.7H2O FeSO4 + 7H2O green pale yellow Describe how you could show that this reaction is reversible. When the iron(sulfate is heated strongly, further decomposition occurs. 2FeSO4→ Fe2O3+ SO2+ SO3The gases formed in this reaction react with water and oxygen to form sulfuric acid. Explain how the sulfuric acid is formed. A mineral of the type FeSO4.xH2O contains 37.2% of water. Complete the calculation to determine x. mass of one mole of H2O = 18 g mass of water in 100 g of FeSO4.xH2O = 37.2 g number of moles of H2O in 100 g of FeSO4.xH2O = mass of FeSO4 in 100 g of FeSO4.xH2O = g mass of one mole of FeSO4 = 152 g number of moles of FeSO4 in 100 g of FeSO4.xH2O = x = When a mixture of sulfur and potassium nitrate is burned and the products are dissolved in water, sulfuric acid is formed. The sulfuric acid formed by this method is not pure. It contains another acid. Deduce the identity of this acid. The heat causes some of the potassium nitrate to decompose. Write the equation for the action of heat on potassium nitrate.
0620_w14_qp_32
THEORY
2014
Paper 3, Variant 2
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Sulfuric acid is made by the Contact process. Sulfur is burned by spraying droplets of molten sulfur into air. Suggest and explain an advantage of using this method. The following equation represents the equilibrium in the Contact process. 2SO2+ O22SO3Oxygen is supplied from the air. The composition of the reaction mixture is 1 volume of sulfur dioxide to 1 volume of oxygen. What volume of air contains 1 dm3 of oxygen? dm3 Sulfur dioxide is more expensive than air. What is the advantage of using an excess of air? The forward reaction is exothermic. The reaction is usually carried out at a temperature between 400 and 450 °C. What is the effect on the position of equilibrium of using a temperature above 450 °C? Explain your answer. What is the effect on the rate of using a temperature below 400 °C? Explain your answer. A low pressure, 2 atmospheres, is used. At equilibrium, about 98% SO3 is present. What is the effect on the position of equilibrium of using a higher pressure? Explain why a higher pressure is not used. Name the catalyst used in the Contact process. Describe how concentrated sulfuric acid is made from sulfur trioxide.
0620_w15_qp_31
THEORY
2015
Paper 3, Variant 1
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Questions Discovered
390