12. Experimental techniques and chemical analysis
A section of Chemistry, 0620
Listing 10 of 677 questions
The table shows the ions present in a 1000 cm3 sample of blood plasma. ion present formula of ion mass present in the 1000 cm3 sample / g sodium Na+ 3.25 potassium K+ 0.16 calcium Ca2+ 0.10 magnesium Mg2+ 0.04 chloride Cl – 3.65 hydrogencarbonate HCO3 – 1.50 phosphate PO4 3– 0.64 sulfate SO4 2– 0.10 Answer these questions using only information from the table. Which positive ion is present in the lowest concentration? Give the name of the compound formed from K+ and Cl – ions. Calculate the mass of potassium ions present in 200 cm3 of this blood plasma.  mass of potassium ions = g When the 1000 cm3 sample of blood plasma is crystallised, several compounds are formed. Suggest the name of the compound which forms the greatest mass of crystals. Describe a test for potassium ions. test result  Blood plasma also contains proteins. Proteins are present in food. Which one of the following substances is also present in food? Draw a circle around the correct answer. carbohydrate hematite polyterylene  CompoundS is one of the monomer units used to make proteins. Its structure is shown. H2N CH compound S CH2 COOH OH On the structure, draw a circle around the alcohol functional group. Deduce the molecular formula of compoundS showing the number of carbon, hydrogen, oxygen and nitrogen atoms. 
0620_w18_qp_31
THEORY
2018
Paper 3, Variant 1
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The table shows the concentrations of the ions present in a solution obtained from cells in the body. ion present formula of ion concentration in mg / 1000 cm3 sodium Na+ potassium K+ calcium Ca2+ magnesium Mg2+ chloride Cl – hydrogencarbonate HCO3 – phosphate PO4 3– Answer these questions using only information from the table. Which negative ion is present in the highest concentration? Calculate the mass of potassium ions present in 250 cm3 of this solution.  mass of potassium ions = mg Calculate the total mass of positive ions present in 1000 cm3 of this solution.  total mass of positive ions = mg Give the name of the compound formed from Na+ and HCO3 – ions. Describe what is observed in these two reactions. ● ● An excess of aqueous sodium hydroxide is added to a solution containing Ca2+ ions. ● ● An excess of aqueous ammonia is added to a solution containing Ca2+ ions.  Lacticacid can build up in muscle cells during exercise. The structure of lacticacid is shown. C COOH OH H CH3 On the structure, draw a circle around the carboxylic acid functional group. Deduce the molecular formula of lacticacid showing the number of carbon, hydrogen and oxygen atoms. Lacticacid can form a polymer. Complete the sentence about polymers using words from the list. atomic large molecular monomers polymers small During polymerisation molecules called join together to form long-chain molecules with a very high relative mass.  
0620_w18_qp_32
THEORY
2018
Paper 3, Variant 2
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The diagrams show the structures of four substances, R, S, T and U. R T U S C C C H H H H H H C C H H H H C C H H H H C C H H H H C C H H H H O C O O C O O C O O C O Ti Ti Ti Ti Ti Ti Ti Ti Ti Ti Ti NH4 + NH4 + Cl – NH4 + NH4 + Cl – NH4 + Cl – Cl – State which one of these substances, R, S, T or U: is an element contains ionic bonds is a gas at room temperature is a polymer. Ammonium chloride is present in some fertilisers. Which two of the following compounds are also present in many fertilisers? Tick two boxes. hydrogen sulfide calcium phosphate copper(fluoride nickel(oxide potassium nitrate  A mixture of ammoniumchloride and aqueous sodiumhydroxide is heated as shown. heat mixture filter paper soaked in methyl orange and acid The filter paper changes colour from red to yellow. Explain why. 
0620_w18_qp_32
THEORY
2018
Paper 3, Variant 2
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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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