12.5. Identification of ions and gases
A subsection of Chemistry, 0620, through 12. Experimental techniques and chemical analysis
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This question is about sulfuric acid, H2SO4. Dilute sulfuric acid and aqueous sodium hydroxide can be used to prepare sodium sulfate crystals using a method that involves titration. The apparatus for titration is shown in . 25.0 cm3 aqueous sodium hydroxide 0.100 mol / dm3 dilute sulfuric acid conical flask Thymolphthalein is used as an indicator for this titration. State the colour change of thymolphthalein at the end-point of this titration. from to Suggest why universal indicator is not used for this titration. 25.0 cm3 of aqueous sodium hydroxide, NaOH, of concentration 0.100 mol / dm3 is neutralised by 20.0 cm3 of dilute sulfuric acid, H2SO4. The equation for the reaction is shown. 2NaOH + H2SO4 → Na2SO4 + 2H2O Calculate the concentration of H2SO4 using the following steps. ● Calculate the number of moles of NaOH used. mol ● Determine the number of moles of H2SO4 that react with the NaOH. mol ● Calculate the concentration of H2SO4. mol / dm3 A student is provided with an aqueous solution of sodium sulfate. Describe how to prepare a pure sample of sodium sulfate crystals from this solution. Potassium hydrogen sulfate, KHSO4, can be prepared by a reaction between aqueous potassium hydroxide and dilute sulfuric acid. Water is the only other product. Write a symbol equation for this reaction. Potassium hydrogen sulfate, KHSO4, dissolves in water to form solution X. Solution X contains K+, H+ and SO4 2– ions. Name the type of solution that contains H+ ions. State the observations when the following tests are done. ● A flame test is carried out on X. ● Solid copper(carbonate is added to X. ● Aqueous barium nitrate acidified with dilute nitric acid is added to X. 0.325 g of Zn is added to dilute sulfuric acid which contains 0.0100 moles of H2SO4. The equation for this reaction is shown. Zn + H2SO4 → ZnSO4 + H2 Determine whether Zn or H2SO4 is the limiting reactant. Explain your answer. In another experiment, 48.0 cm3 of hydrogen gas, H2, is produced. The experiment is carried out at room temperature and pressure, r.t.p. Calculate the number of molecules in 48.0 cm3 of H2 gas measured at r.t.p. The value of the Avogadro constant is 6.02 × 1023. molecules
0620_w24_qp_43
THEORY
2024
Paper 4, Variant 3
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Aqueous ammonia is an alkali. Complete the dot-and-cross diagram to show the electron arrangement in a molecule of ammonia. H N H H  Complete the word equation for the reaction of aqueous ammonia with dilute hydrochloricacid. ammonia + hydrochloric acid  Describe the colour change when excess aqueous ammonia is added to an acidified solution of methylorange. from to ���������������������������������������������������������������� Aqueous ammonia reacts with aqueous copper(ions to produce compoundB. The formula of compoundB is CuN4H16O2. Complete the table to calculate the relative molecular mass of compoundB. type of atom number of atoms relative atomic mass copper 1 × 64 = 64 nitrogen 4 × 14 = 56 hydrogen oxygen  relative molecular mass =  Ammonia is used in the production of fertilisers. State why farmers put fertilisers on the soil where crops are to be grown. 
0620_m21_qp_32
THEORY
2021
Paper 3, Variant 2
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