12. Experimental techniques and chemical analysis
A section of Chemistry, 0620
Listing 10 of 677 questions
The table shows the mass of each type of ion present in a 100 cm3 sample of milk. name of ion formula of ion mass of ion present in 100 cm3 milk / mg calcium Ca2+ chloride Cl – Mg2+ phosphate PO4 3– potassium K+ sodium Na+ SO4 2– negative ions of organic acids Calculate the mass of calcium ions present in a 20 cm3 sample of this milk.  mass of calcium ions = mg Which positive ion is present in the highest concentration in this sample of milk? Name the compound formed from Mg2+ and SO4 2– ions. Describe a test for chloride ions. test result  One of the organic acids present in milk is lactic acid. The structure of lactic acid is shown. C C O O H O H C H H H H On the structure shown draw a circle around the carboxylic acid functional group. Deduce the molecular formula of lactic acid showing the number of carbon, hydrogen and oxygen atoms. Ethanoic acid is another organic acid. The reduction of ethanoic acid produces ethanol. What is meant by the term reduction? The molecular formula of ethanol is C2H6O. Complete the table to calculate the relative molecular mass of ethanol. number of atoms relative atomic mass carbon 2 × 12 = 24 hydrogen oxygen  relative molecular mass = 
0620_m18_qp_32
THEORY
2018
Paper 3, Variant 2
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Limestone rock is mainly calciumcarbonate, CaCO3. The ‘limestone cycle’ is shown. Each step is numbered. limestone calcium carbonate CaCO3limewater calcium hydroxide Ca(OH)2slaked lime calcium hydroxide Ca(OH)2lime step 2 add limited water step 4 add CO2 step 3 add an excess of water step 1 heat Complete the box to give the chemical name and formula of lime. Which step involves a physical change? What type of reaction is step1? Suggest how step2 could be reversed. Write a chemical equation for step4. Explain why step4 is a neutralisation reaction. Refer to the substances reacting in your answer. Dolomite is a similar rock to limestone. Dolomite contains magnesiumcarbonate, MgCO3. Write a chemical equation for the reaction between magnesiumcarbonate and dilute nitricacid. Forsterite is another rock which contains a magnesium compound. A sample of forsterite has the following composition by mass: Mg, 2.73 g; Si, 1.58 g; O, 3.60 g. Calculate the empirical formula of forsterite.  empirical formula = 
0620_m18_qp_42
THEORY
2018
Paper 4, Variant 2
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A list of compounds is shown. aluminium oxide calcium bromide calcium oxide ethane ethene hydrogen chloride methane nitrogen dioxide potassium iodide potassium manganate(sodium chloride Answer the following questions using only the compounds in the list. Each compound may be used once, more than once or not at all. Which compound: when in acidified solution, is used to test for sulfurdioxide is the main constituent of natural gas when dissolved in water, gives a yellow precipitate on addition of acidified aqueous silvernitrate is used in flue gas desulfurisation to neutralise acidic gases is a reactant used in the manufacture of ethanol? What is the meaning of the term compound ? Complete the electronic structure of a molecule of hydrogen chloride. Show only the outer shell electrons. Cl H  
0620_m20_qp_32
THEORY
2020
Paper 3, Variant 2
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The table shows the mass of some of the ions in a 1000 cm3 sample of sea water. name of ion formula of ion mass of ion in 1000 cm3 of sea water / mg bromide Br – calcium Ca2+ chloride Cl – 18 980 hydrogencarbonate HCO3 – magnesium Mg2+ metaborate B3O6 3– K+ sodium Na+ 10 556 strontium Sr2+ SO4 2– Answer these questions using only the information in the table. State which negative ion has the lowest mass in 1000 cm3 of sea water. Give the formulae of the ions in potassiumsulfate. and Calculate the mass of calcium ions in 200 cm3 of this sample of sea water.  mass = mg A sample of this sea water is evaporated. State the name of the compound which is present in the greatest quantity when this sample is evaporated. Give the name of the ion which reacts with aqueous silvernitrate to give a cream precipitate. The B3O6 3– ion can be converted to boric acid, H3BO3. Boricacid is also produced when borontrichloride, BCl 3, reacts with water. Complete the equation for this reaction. BCl 3 + H2O → H3BO3 + HCl  The symbol of a strontium ion is shown. 87Sr2+ Deduce the number of electrons, protons and neutrons in one atom of this strontium ion. number of electrons number of protons number of neutrons  Some isotopes of strontium are radioactive. Give one medical use of radioactive isotopes. The isotope 235U is also radioactive. State the major use of this isotope of uranium. 
0620_m21_qp_32
THEORY
2021
Paper 3, Variant 2
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A student wanted to make some zincchloride crystals. The student followed the procedure shown. step 1 Add excess zinc powder to dilute hydrochloricacid to form aqueous zincchloride. step 2 Remove unreacted zinc powder from the aqueous zincchloride. step 3 Heat the solution until it is saturated. step 4 Allow the saturated solution to cool and remove the crystals that form. Write the equation for the reaction in step1. Include state symbols. Explain why excess zinc powder is added in step1. Suggest how unreacted zinc powder is removed in step2. A saturated solution is formed in step3. Suggest what is meant by the term saturated solution. Explain why crystals form as the solution cools in step4. Name two zinc compounds which react with dilute hydrochloricacid to form zincchloride. If excess calcium metal is used instead of excess zinc powder in step1, pure calciumchloride crystals do not form. Explain why. Some salts can be made by titration. In a titration experiment, 20.0 cm3 of aqueous sodiumhydroxide reacts exactly with 25.0 cm3 of 0.100 mol / dm3 dilute sulfuricacid to make sodium sulfate. 2NaOH+ H2SO4→ Na2SO4+ 2H2OCircle the name of the type of reaction that takes place. decomposition neutralisation precipitation reduction  Calculate the concentration of the aqueous sodiumhydroxide in g / dm3 using the following steps. ● Calculate the number of moles of dilute sulfuricacid used.  mol ● Determine the number of moles of sodium hydroxide which react with the dilute sulfuricacid.  mol ● Calculate the concentration of the aqueous sodiumhydroxide in mol / dm3.  mol / dm3 ● Calculate the concentration of the aqueous sodiumhydroxide in g / dm3.  g / dm3  
0620_m21_qp_42
THEORY
2021
Paper 4, Variant 2
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