12. Experimental techniques and chemical analysis
A section of Chemistry, 0620
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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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