12.5. Identification of ions and gases
A subsection of Chemistry, 0620, through 12. Experimental techniques and chemical analysis
Listing 10 of 359 questions
Table2.1 shows the masses of some of the ions in a 1000 cm3 sample of river water. Table 2.1 name of ion formula of ion mass of ion in 1000 cm3 of river water / mg NH4 + 0.4 calcium Ca2+ 1.4 chloride Cl – 0.1 hydrogencarbonate HCO3 – 1.2 magnesium Mg2+ 0.6 nitrate NO3 – 0.8 phosphate PO4 3– 1.3 sodium Na+ 0.5 SO4 2– 0.4 Answer these questions using the information in Table2.1. Name the negative ion that has the highest concentration. Name the compound that contains NH4 + and SO4 2– ions only. Calculate the mass of hydrogencarbonate ions in 200 cm3 of river water.  mass = mg Give a test for sodium ions. test observations  Most of the nitrate ions in river water come from fertilisers used on fields. Describe the benefit of using fertilisers. Water from natural sources can be polluted with harmful substances. State why sewage and phosphates in river water are harmful. sewage phosphates  River water can contain acids such as ethanoic acid and methylbutanoic acid. Draw the displayed formula for ethanoic acid.  Ethanoic acid reacts with sodium hydroxide. Complete the word equation for this reaction. ethanoic acid + sodium hydroxide → +  Methylbutanoic acid has the molecular formula C5H10O2. Complete Table 2.2 to calculate the relative molecular mass of C5H10O2. Table 2.2 atom number of atoms relative atomic mass carbon 5 × 12 = 60 hydrogen oxygen  relative molecular mass = 
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THEORY
2024
Paper 3, Variant 2
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This question is about acids, bases and alkalis. Table 3.1 shows the pH values of some substances. Table 3.1 substance pH NaOH14 Ca(OH)210 H2O7 CH3COOH4 HNO31 Define the term base. State what is meant by the term alkali. Thymolphthalein is an indicator. State the colour of thymolphthalein in: ● NaOH● CH3COOH.  Use the information in Table 3.1 to identify the substance with the highest concentration of H+ions. Explain your answer. substance explanation  Name an indicator which can be used to identify the substance with the highest concentration of H+ions. Complete the equation to show the dissociation of ethanoic acid, CH3COOH, in aqueous solution. CH3COOHWrite the ionic equation which represents a neutralisation reaction between any acid and any alkali. Dilute nitric acid, HNO3, reacts with aqueous calcium hydroxide, Ca(OH)2, as shown. 2HNO3+ Ca(OH)2→ Ca(NO3)2+ 2H2O20.0 cm3 of 0.0150 mol / dm3 Ca(OH)2reacts with 25.0 cm3 of HNO3. Calculate the concentration of HNO3in g / dm3. Use the following steps. ● Calculate the number of moles of Ca(OH)2used.  mol ● Determine the number of moles of HNO3which react with the Ca(OH)2.  mol ● Calculate the concentration of HNO3in mol / dm3.  mol / dm3 ● Calculate the concentration of HNO3in g / dm3.  g / dm3  
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THEORY
2024
Paper 4, Variant 2
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Use A student collected some water from a polluted river. The water contained soluble solids and insoluble clay and had a pH of 5. How can the student separate the clay from the rest of the river water? The student uses litmus paper to show that the river water is acidic. What will be the result of this test? The student then boiled the river water to obtain the soluble solids. The diagram shows how she heated the water. steel can copper gauze iron tripod boiling water natural gas steam Which of the substances named in the diagram is an alloy, a compound which is liquid at room temperature, an element, a fuel? Name the main substance in natural gas. What is the normal temperature of boiling water? Examiner's Use After the student boiled off the water, she analysed the white powder on the inside of the steel can. The table shows her results. name of ion formula of ion mass of ion present /milligrams calcium Ca2+ carbonate CO3 2– chloride Cl – nitrate NO3 – sodium Na+ sulphate SO4 2– Which positive ion had the greatest concentration in the sample of river water? Complete the following equation to show how a sodium ion is formed from a sodium atom. Na Na+ + Instead of using natural gas, the student could have used butane to heat the water. The formula of butane is C4H10. What products are formed when butane burns in excess air? Name the poisonous gas formed when butane undergoes incomplete combustion.
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THEORY
2005
Paper 2, Variant 0
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For Examiner's Use The Carlsbad caverns in New Mexico are very large underground caves. Although the walls of these caves are coated with gypsum (hydrated calcium sulphate), the caves have been formed in limestone. It is believed that the caves were formed by sulphuric acid reacting with the limestone. Complete the word equation. calcium + sulphuric calcium + + carbonate acid sulphate Describe how you could test the water entering the cave to show that it contained sulphate ions. test result How could you show that the water entering the cave has a high concentration of hydrogen ions? Hydrogen sulphide gas which was escaping from nearby petroleum deposits was being oxidised to sulphuric acid. Complete the equation for this reaction forming sulphuric acid. H2S + O2 Explain why all the hydrogen sulphide should be removed from the petroleum before it is used as a fuel. For Examiner's Use Draw a diagram to show the arrangement of the valency electrons in one molecule of the covalent compound hydrogen sulphide. Use o to represent an electron from a sulphur atom. Use x to represent an electron from a hydrogen atom. Sulphuric acid is manufactured by the Contact Process. Sulphur dioxide is oxidised to sulphur trioxide by oxygen. 2SO2 + O2 2SO3 Name the catalyst used in this reaction. What temperature is used for this reaction? Describe how sulphur trioxide is changed into sulphuric acid. Gypsum is hydrated calcium sulphate, CaSO4.xH2O. It contains 20.9% water by mass. Calculate x. Mr: CaSO4, 136; H2O, 18. 79.1 g of CaSO4 = moles 20.9 g of H2O = moles x =
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THEORY
2005
Paper 3, Variant 0
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Use The diagram shows a cross section of a soil. decaying leaves topsoil subsoil limestone A student took 10 g of topsoil and shook it with 200 cm3 of distilled water. How can the student separate the solids in the soil from the solution? The topsoil had a pH of 6. Which of the following gives the best description of this pH? Tick one box. strongly acidic weakly acidic neutral weakly alkaline Examiner's Use The soil contained large amounts of calcium ions and carbonate ions. Use the information in the diagram to suggest where these ions came from. Complete the word equation for the reaction of calcium carbonate with hydrochloric acid. calcium carbonate + + hydrochloric acid calcium chloride + The table shows the mass of each ion present in 200 cm3 of soil solution. ion formula of ion mass present/milligrams calcium Ca2+ carbonate - CO iron(Fe3+ magnesium Mg2+ nitrate - NO phosphate - PO others Which negative ion has the highest concentration in the soil solution? Calculate the mass of iron(ions in one litre (1000 cm3) of solution. Which ion in the table will release ammonia when heated with aqueous sodium hydroxide and aluminium foil? Describe a test for iron(ions. test result Examiner's Use The air trapped in the soil has a different composition from the air in the atmosphere. The table shows the composition of the air in the soil. gas percentage of gas in soil air carbon dioxide nitrogen oxygen other gases State how the composition of soil air compares with the composition of air in the atmosphere. carbon dioxide nitrogen oxygen Decaying leaves produce ethanoic acid. Complete the formula for ethanoic acid showing all atoms and bonds. C C H H H
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THEORY
2006
Paper 2, Variant 0
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Use Four bottles were known to contain aqueous ammonia, dilute hydrochloric acid, sodium hydroxide solution and vinegar, which is dilute ethanoic acid. The bottles had lost their labels. The pH values of the four solutions were 1, 4, 10 and 13. Complete the table. solution pH aqueous ammonia dilute hydrochloric acid sodium hydroxide solution vinegar The following apparatus was set up to investigate the electrical conductivity of dilute acids. + _ carbon anode bulb/lamp carbon cathode dilute sulphuric acid bubbles of oxygen gas bubbles of hydrogen gas Dilute sulphuric acid is a strong acid. If it was replaced by a weak acid, what two differences in the observations would you expect to make? When nitric acid is added to water the following reaction occurs. HNO3 + H2O - NO + H3O+ Give the name and the formula of the particle which is transferred from nitric acid to water. name formula Examiner's Use This question is concerned with the following oxides. aluminium oxide Al2O3 calcium oxide CaO carbon dioxide CO2 carbon monoxide CO magnesium oxide MgO sulphur dioxide SO2 Which of the above oxides will react with hydrochloric acid but not with aqueous sodium hydroxide? Which of the above oxides will react with aqueous sodium hydroxide but not with hydrochloric acid? Which of the above oxides will react both with hydrochloric acid and with aqueous sodium hydroxide? Which of the above oxides will react neither with hydrochloric acid nor with aqueous sodium hydroxide?
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THEORY
2006
Paper 3, Variant 0
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