7.3. Preparation of salts
A subsection of Chemistry, 0620, through 7. Acids, bases and salts
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This question is about salts. Salts that are insoluble in water are made by precipitation. ● Lead(iodide, PbI2, is insoluble in water. ● All nitrates are soluble in water. ● All sodium salts are soluble in water. You are provided with solid lead(nitrate, Pb(NO3)2, and solid sodiumiodide, NaI. Describe how you would make a pure sample of lead(iodide by precipitation. Your answer should include: ● practical details ● a chemical equation for the precipitation reaction. Nitrates decompose when heated. When hydrated zincnitrate is heated, oxygen gas is given off. Describe a test for oxygen. test observations  Complete the equation for the decomposition of hydrated zincnitrate. 2Zn(NO3)2•6H2O → ZnO + NO2 + O2 + H2O Some sulfates are hydrated. When hydrated sodiumsulfate crystals, Na2SO4•xH2O, are heated, they give off water. Na2SO4•xH2O→ Na2SO4+ xH2OA student carries out an experiment to determine the value of x in Na2SO4•xH2O. step 1 Hydrated sodiumsulfate crystals are weighed. step 2 The hydrated sodiumsulfate crystals are then heated. step 3 The remaining solid is weighed. Describe how the student can check that all the water has been given off. In an experiment, 1.61 g of Na2SO4•xH2O is heated until all the water is given off. The mass of Na2SO4 remaining is 0.71 g. [Mr: Na2SO4,142; H2O,18] Determine the value of x using the following steps. ● Calculate the number of moles of Na2SO4 remaining.  mol ● Calculate the mass of H2O given off.  g ● Calculate the number of moles of H2O given off.  mol ● Determine the value of x.  x =  
0620_s21_qp_41
THEORY
2021
Paper 4, Variant 1
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