12.5. Identification of ions and gases
A subsection of Chemistry, 0620, through 12. Experimental techniques and chemical analysis
Listing 10 of 359 questions
The diagram below shows the apparatus which can be used to obtain pure water from sea-water. heat sea-water pure water State the name of this process. Label the boxes on the diagram above with the correct names of the pieces of apparatus shown. Complete the following sentences using words from the list below. boils condenses cools freezes higher lower melts Water has a boiling point than salt. When a solution of salt is heated strongly, the water and escapes as steam. When the steam cools, it back to liquid water. The table shows the concentration of the seven most abundant compounds in sea-water. compound ions present concentration in g / m3 calcium carbonate Ca2+ and CO3 2– calcium sulfate Ca2+ and SO4 2– 1 800 magnesium chloride Mg2+ and Cl – 6 800 magnesium sulfate 5 700 potassium bromide K+ and Br – potassium chloride K+ and Cl – sodium chloride Na+ and Cl – 28 000 Which negative ion is present in the greatest concentration in sea-water? Which positive ion is present in the lowest concentration in sea-water? Write the formulae of the two ions present in magnesium sulfate.
0620_w13_qp_22
THEORY
2013
Paper 2, Variant 2
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The diagram shows a kiln for making lime (calcium oxide) from limestone (calcium carbonate). A B D C brick lime kiln Which letter on the diagram above shows where the limestone is added, where the waste gases exit from the kiln? Complete the symbol equation for the decomposition of limestone. CaCO3 → CaO + When 50 g of calcium carbonate is decomposed, 28 g of calcium oxide is formed. Calculate the minimum mass of calcium carbonate needed to produce 8.4 g of calcium oxide. The table below shows the temperatures at which some Group II carbonates decompose. Group II carbonate temperature at which Group II carbonates decompose / °C beryllium carbonate magnesium carbonate calcium carbonate Describe the pattern in the ease of decomposition of Group II carbonates. Predict the decomposition temperature of barium carbonate. °C Lime is calcium oxide. State one use of lime. What type of oxide is calcium oxide? Calculate the relative formula mass of calcium oxide. Use your Periodic Table to help you. Calcium is extracted from its compounds by electrolysis. Suggest why calcium is extracted by electrolysis rather than by reduction with carbon.
0620_w13_qp_22
THEORY
2013
Paper 2, Variant 2
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A mixture of soil and water was shaken and then fi ltered. Draw a labelled diagram of the apparatus you would use for separating the insoluble particles of soil from the solution. The fi ltrate was then evaporated. The table shows the composition and mass of each compound obtained by evaporating the fi ltrate. compound ions present in the compound mass of compound / g calcium carbonate Ca2+ and CO3 2– 4.0 calcium sulfate Ca2+ and SO4 2– 5.0 magnesium sulfate Mg2+ and SO4 2– 2.8 K+ and NO3 – 1.2 potassium sulfate K+ and SO4 2– 2.4 sodium carbonate 3.0 sodium chloride Na+ and Cl – 1.6 State the name of the compound which contains K+ and NO3 – ions. Write the symbols for the ions present in sodium carbonate. Which compound with a singly charged negative ion has the highest mass in the mixture? The table from page 7 is repeated below: compound ions present in the compound mass of compound / g calcium carbonate Ca2+ and CO3 2– 4.0 calcium sulfate Ca2+ and SO4 2– 5.0 magnesium sulfate Mg2+ and SO4 2– 2.8 K+ and NO3 – 1.2 potassium sulfate K+ and SO4 2– 2.4 sodium carbonate 3.0 sodium chloride Na+ and Cl – 1.6 Calculate: the total mass of all the compounds present in the mixture, the percentage of magnesium sulfate by mass in the mixture. Calcium carbonate decomposes when heated. Complete the symbol equation for this reaction. CaCO3 → CaO + Calcium oxide, CaO, reacts with water to form a strongly alkaline solution. Which one of the following pH values is strongly alkaline? Put a ring around the correct answer. pH 3 pH 7 pH 8 pH 12
0620_w14_qp_23
THEORY
2014
Paper 2, Variant 3
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Rubidium and strontium are very reactive metals at the top of the reactivity series. Because their ions have different charges, their compounds behave differently when heated. The formulae of the ions of these two elements are Rb+ and Sr2+. Explain why these metals, which are in different groups, form ions which have different charges. Strontium carbonate is similar to calcium carbonate. It is insoluble in water and it decomposes when heated. Rubidium carbonate is soluble in water and does not decompose when heated. Describe a method to prepare a pure sample of the insoluble salt, strontium carbonate, by precipitation. Complete the equation for the decomposition of strontium carbonate. SrCO3 → + Metal nitrates decompose when heated. Rubidium nitrate decomposes as follows: 2RbNO3 → 2RbNO2 + O2 What is the name of the compound RbNO2? The nitrates of most other metals decompose in a different way. Complete the equation for the decomposition of strontium nitrate. Sr(NO3)2 → + 4NO2 +
0620_w14_qp_33
THEORY
2014
Paper 3, Variant 3
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The structures of six compounds are shown below. Al Cl Cl Cl Cl Al Cl Cl Cl A C C H H H H SO4 2– B D F E O H H Ba2+ NH4 + NH4 + NH4 + NH4 + SO4 2– NH4 + NH4 + SO4 2– NH4 + NH4 + SO4 2– NH4 + SO4 2– NH4 + NH4 + SO4 2– NH4 + H Cl – Cl – Cl – Cl – Ba2+ Cl – Cl – Ba2+ Cl – Cl – Ba2+ Cl – Ba2+ Cl – Cl – Ba2+ Cl – Answer the following questions about these substances. Each compound may be used once, more than once or not at all. Which substance, A, B, C, D, E or F, gives a white precipitate on addition of an aqueous solution of sodium sulfate, is a component of many fertilisers, contains a Group III element, is an acidic gas at room temperature, turns anhydrous cobalt chloride pink, is the main component of natural gas? Compound A can be made by direct combination of chlorine and aluminium using the apparatus shown below. chlorine excess chlorine aluminium foil compound A Al 2Cl 6 On the diagram above, draw an arrow to show where heat is applied. Suggest one safety precaution that should be taken when carrying out this experiment. Complete the symbol equation for this reaction. 2Al + Cl 2 → Al 2Cl 6
0620_w15_qp_21
THEORY
2015
Paper 2, Variant 1
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Hydrogen chloride can be prepared in the laboratory by heating sodium chloride with concentrated sulfuric acid using the apparatus shown below. sodium chloride concentrated sulfuric acid Complete the diagram by adding the labels in the boxes. The equation for the reaction is shown below. 2NaCl + H2SO4 → Na2SO4 + 2HCl State the name of the salt formed as a product in this reaction. Hydrogen chloride gas dissolves in water to form hydrochloric acid. The diagram below shows the apparatus used to electrolyse concentrated hydrochloric acid. X Y + – Label the diagram to show • the anode, • the cathode, • the electrolyte. Give the names of the gases collected at X, Y. Complete the word equation for the reaction of hydrochloric acid with calcium carbonate. hydrochloric acid + calcium carbonate → + + Aqueous ammonia is added slowly to a beaker containing hydrochloric acid. The graph below shows how the pH of the solution in the flask changes as the aqueous ammonia is added. pH volume of aqueous ammonia / cm3 What was the pH of the hydrochloric acid at the start of the experiment? Describe how the pH of the solution changes as the titration proceeds.
0620_w15_qp_23
THEORY
2015
Paper 2, Variant 3
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Questions Discovered
359