7.3. Preparation of salts
A subsection of Chemistry, 0620, through 7. Acids, bases and salts
Listing 10 of 150 questions
Soluble salts can be made using a base and an acid. Complete this method of preparing dry crystals of the soluble salt cobalt(chloride-6-water from the insoluble base cobalt(carbonate. Step 1 Add an excess of cobalt(carbonate to hot dilute hydrochloric acid. Step 2 Step 3 Step 4 6.0 g of cobalt(carbonate was added to 40 cm3 of hydrochloric acid, concentration 2.0 mol / dm3. Calculate the maximum yield of cobalt(chloride-6-water and show that the cobalt(carbonate was in excess. CoCO3 + 2HCl → CoCl 2 + CO2 + H2O CoCl 2 + 6H2O → CoCl 2.6H2O Maximum yield Number of moles of HCl used = Number of moles of CoCl 2 formed = Number of moles of CoCl 2.6H2O formed = Mass of one mole of CoCl 2.6H2O = 238 g Maximum yield of CoCl 2.6H2O = g To show that cobalt(carbonate is in excess Number of moles of HCl used = (use value from above) Mass of one mole of CoCO3 = 119 g Number of moles of CoCO3 in 6.0 g of cobalt(carbonate = Explain why cobalt(carbonate is in excess
0620_w10_qp_31
THEORY
2010
Paper 3, Variant 1
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Soluble salts can be made by the neutralisation of an acid by a base. Insoluble salts can be made by precipitation. The following is a brief description of the preparation of the soluble salt, nickel(chloride-6-water, from the insoluble base nickel(carbonate. Nickel(carbonate is added in small amounts to hot dilute hydrochloric acid until it is in excess. The mixture is fi ltered. The fi ltrate is partially evaporated and then allowed to cool until crystals of nickel(chloride-6-water form. Why is it necessary to use excess carbonate? Explain why it is necessary to fi lter. Why partially evaporate rather than evaporate to dryness? What additional steps are needed to obtain dry crystals? Potassium chloride can be made from hydrochloric acid and potassium carbonate. Why must a different experimental method be used for this preparation? Give a description of the different method used for this salt preparation. Insoluble salts are made by precipitation. An equation for the preparation of barium sulfate is given below. BaCl 2+ MgSO4→ BaSO4+ MgCl 2This reaction can be used to fi nd x in the formula for hydrated magnesium sulfate MgSO4.xH2O. A known mass of hydrated magnesium sulfate, MgSO4.xH2O, was dissolved in water. Excess aqueous barium chloride was added. The precipitate of barium sulfate was fi ltered, washed and dried. Finally it was weighed. Mass of hydrated magnesium sulfate = 1.476 g Mass of barium sulfate formed = 1.398 g The mass of one mole of BaSO4 = 233 g The number of moles of BaSO4 formed = The number of moles of MgSO4.xH2O = The mass of one mole of MgSO4.xH2O = g The mass of one mole of MgSO4 = 120 g The mass of xH2O in one mole of MgSO4.xH2O = x =
0620_w11_qp_32
THEORY
2011
Paper 3, Variant 2
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Questions Discovered
150