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 table shows the concentrations of the ions present in the solution obtained from squid nerve cells and in human blood plasma. ion present solution obtained from squid nerve cells human blood plasma concentration in g / 1000 cm3 concentration in g / 1000 cm3 sodium 1.15 3.25 potassium 15.60 0.16 magnesium 0.03 0.04 chloride 3.55 3.65 hydrogencarbonate trace 1.50 Answer these questions using only information from the table. Give two major differences between the concentrations of the ions present in the solution obtained from squid nerve cells and in human blood plasma.  Calculate the mass of potassium ions present in 250 cm3 of the solution obtained from squid nerve cells.  mass of potassium ions = g Describe a test for sodium ions. test result  Squid produce an ink which contains a compound called taurine. The structure of taurine is shown. S O O C H H C N H H H H O H Deduce the molecular formula of taurine showing the number of carbon, hydrogen, oxygen, nitrogen and sulfur atoms. The ink used for writing is a mixture of dyes. These dyes can be separated by paper chromatography. Describe how to separate a mixture of dyes using paper chromatography. Include a labelled diagram in your answer.  
0620_w18_qp_33
THEORY
2018
Paper 3, Variant 3
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Copper(nitrate decomposes when heated. Two gases, oxygen and nitrogendioxide, and a solid are made in the reaction. A sample of copper(nitrate was decomposed using the apparatus shown. X aqueous sodium hydroxide copper(nitrate heat water Complete the chemical equation for the reaction. 2Cu(NO3)2 O2 + NO2 +  Only oxygen gas is collected at X. Explain why. Nitrogen dioxide and other oxides of nitrogen are formed in car engines. Explain how nitrogen dioxide is formed in car engines. A teacher heated 18.8 g of copper(nitrate. Calculate the number of moles of copper(nitrate present in the 18.8 g. mol Calculate the maximum number of moles of oxygen that can be made by heating 18.8 g of copper(nitrate. mol Calculate the maximum volume of oxygen at room temperature and pressure, in cm3, that can be made by heating 18.8 g of copper(nitrate. cm3 A sample of copper(nitrate was dissolved in water to form an aqueous solution. The aqueous solution was split into three portions. A separate test was done on each portion as shown. test reagent added result aqueous sodium hydroxide light blue precipitate forms zinc powder solution changes from blue to colourless and a brown solid forms ammonia gas is produced Give the formula of the light blue precipitate formed in test1. Explain the changes seen in test2. Identify the two reagents that must be added to the aqueous copper(nitrate in test3.  Copper(nitrate can be made by reacting copper(carbonate with nitricacid. One of the products is carbon dioxide. Write a chemical equation for the reaction of copper(carbonate with nitricacid. Carbondioxide is added to the air by living things. Name the chemical process by which living things add carbondioxide to the air. Carbondioxide is removed from the air by plants. Name the chemical process by which plants remove carbon dioxide from the air. 
0620_w18_qp_41
THEORY
2018
Paper 4, Variant 1
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Dilute sulfuricacid and aqueous potassiumhydroxide can be used to make potassiumsulfate crystals using a method that includes titration. conical flask dilute sulfuric acid 25.0 cm3 of aqueous potassium hydroxide A student titrated 25.0 cm3 of 0.0500 mol / dm3 aqueous potassium hydroxide with dilute sulfuric acid in the presence of an indicator. The volume of dilute sulfuric acid needed to neutralise the aqueous potassiumhydroxide was 20.0 cm3. The equation for the reaction is shown. H2SO4 + 2KOH K2SO4 + 2H2O Determine the concentration of the dilute sulfuricacid. ● Calculate the number of moles of aqueous potassium hydroxide used.  mol ● Calculate the number of moles of dilute sulfuric acid needed to neutralise the aqueous potassiumhydroxide.  mol ● Calculate the concentration of the dilute sulfuric acid.  mol / dm3 After the titration has been completed, the conical flask contains an aqueous solution of potassiumsulfate and some of the dissolved indicator. Describe how to prepare a pure, dry sample of potassiumsulfate crystals from new solutions of dilute sulfuricacid and aqueous potassiumhydroxide of the same concentrations as used in the titration. Include a series of key steps in your answer. Potassiumhydrogensulfate, KHSO4, is an acid salt. It dissolves in water to produce an aqueous solution, X, containing K+, H+ and SO4 2– ions. Describe what you would see when the following experiments are done. Magnesium ribbon is added to an excess of solutionX. A flame test is done on solutionX. An aqueous solution containing bariumions is added to solutionX. Dilute sulfuricacid reacts with bases, metals and carbonates. Write chemical equations for the reaction of dilute sulfuricacid with each of the following: magnesium hydroxide zinc sodium carbonate
0620_w18_qp_43
THEORY
2018
Paper 4, Variant 3
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This question is about ammonia. When ammonia gas reacts with hydrogenchloride gas, white fumes of ammoniumchloride are formed. NH3 + HCl NH4Cl What type of chemical reaction is this? Draw a circle around the correct answer. decomposition neutralisation oxidation reduction Watch-glasses of aqueous ammonia and concentrated hydrochloricacid were placed near each other on a table. At first no white fumes were seen. After a short time, white fumes were seen between the watch-glasses. watch-glass of ammonia watch-glass of hydrochloric acid at the start a short time later dense white fumes Explain these observations using the kinetic particle model. Ammonia is used in the manufacture of fertilisers. Name the three elements present in most fertilisers which improve plant growth.  Aqueous ammonia can be used to test for aluminium ions and zinc ions. Complete the table to show the expected observations. ion observation on adding a small volume of aqueous ammonia observation on adding an excess of aqueous ammonia aluminium (Al 3+) zinc (Zn2+)  
0620_w19_qp_31
THEORY
2019
Paper 3, Variant 1
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This question is about compounds of nitrogen. Aqueous ammonia is alkaline. Which one of the following pH values could be the pH of aqueous ammonia? Draw a circle around the correct answer. pH 1 pH 5 pH 7 pH 9 Ammonia has a strong smell. A beaker of aqueous ammonia was placed in front of a class of students. At first, the students at the back of the class could not smell the ammonia. After a few minutes they could smell the ammonia. Explain these observations using the kinetic particle model. Ammonia is used in the manufacture of nitric acid. Balance the chemical equation for the first step in the process. 4NH3 + 5O2 NO + 6H2O The reaction is exothermic. What is meant by the term exothermic? The NO produced in the first step then reacts with oxygen to produce nitrogendioxide, NO2. 2NO + O2 2NO2 How does this equation show that NO is oxidised? Is nitrogen dioxide an acidic oxide or a basic oxide? Give a reason for your answer. Oxides of nitrogen are atmospheric pollutants. State one adverse effect of oxides of nitrogen on health. Ammonia reacts with nitricacid to form a salt which is present in many fertilisers. Name the salt formed when ammonia reacts with nitricacid. 
0620_w19_qp_32
THEORY
2019
Paper 3, Variant 2
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This question is about ions and ionic compounds. Choose from the following list of ions to answer the questions. Br – Ca2+ Cl – Cr3+ Cu2+ K+ Li+ Na+ SO3 2– SO4 2– Each ion may be used once, more than once or not at all. State which ion: gives a lilac colour in a flame test forms a grey-green precipitate with aqueous ammonia forms a white precipitate with aqueous sodium hydroxide forms a cream precipitate with acidified aqueous silver nitrate forms a white precipitate with acidified aqueous barium nitrate. Describe how to do a flame test on a sample of a salt. Magnesiumphosphate contains magnesium ions, Mg2+, and phosphate ions, PO4 3–. Deduce the formula of magnesiumphosphate. 
0620_w19_qp_41
THEORY
2019
Paper 4, Variant 1
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This question is about sulfuricacid and substances that can be made from sulfuricacid. Sulfuric acid is a strong acid. What is meant by the term strong acid ? strong acid  Dilute sulfuricacid and aqueous sodiumhydroxide are used to make aqueous sodiumsulfate, Na2SO4, or aqueous sodiumhydrogensulfate, NaHSO4. The method includes use of the following apparatus. conical flask dilute sulfuric acid 25.0 cm3 of aqueous sodium hydroxide 25.0 cm3 of aqueous sodiumhydroxide of concentration 0.100 mol / dm3 was neutralised by 25.0 cm3 of dilute sulfuricacid of concentration 0.0500 mol / dm3. The equation for the reaction is shown. This is reaction1. 2NaOH+ H2SO4Na2SO4+ 2H2O reaction 1 The same technique and the same solutions can be used to make aqueous sodiumhydrogensulfate. The equation for the reaction is shown. This is reaction2. NaOH+ H2SO4NaHSO4+ H2O reaction 2 Complete the table to calculate the volume of dilute sulfuricacid that reacts with 25.0 cm3 of aqueous sodiumhydroxide in reaction2. volume of 0.0500 mol / dm3 dilute sulfuric acid in cm3 volume of 0.100 mol / dm3 aqueous sodium hydroxide in cm3 reaction 1 25.0 25.0 reaction 2 25.0  Aqueous sodium hydrogen sulfate, NaHSO4, contains the ions Na+, H+and SO4 2–. Describe what you would see if the following experiments were done. A flame test was done on aqueous sodiumhydrogensulfate. Solid copper(oxide was added to aqueous sodiumhydrogensulfate and the mixture was warmed. A test can be done to show the presence of SO4 2–by adding acidified aqueous bariumchloride or acidified aqueous bariumnitrate. State the observation that would show that SO4 2– is present. Write an ionic equation for the reaction that occurs if SO4 2– is present. Include state symbols. 
0620_w19_qp_43
THEORY
2019
Paper 4, Variant 3
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Questions Discovered
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