Chemistry · Oct / Nov 2024 · Paper 42 · Question 4
0620
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Silver bromide, AgBr, is made when aqueous silver ethanoate, CH3COOAg, is added to aqueous sodium bromide, NaBr. The equation for the reaction is shown in equation 1. equation 1 CH3COOAg + NaBr CH3COONa + AgBr The method includes the following steps. step 1 Add 200.0 cm3 of 0.0500 mol / dm3 CH3COOAg to a beaker. This volume contains 0.0100 mol of Ag+ ions. step 2 Add 50.0 cm3 of aqueous NaBr. This volume contains 0.0100 mol of Br – ions. A precipitate forms. step 3 Filter the mixture. step 4 Dry the solid residue until all the water is removed. step 5 Record the mass of the dry residue.
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4(a)[1]
Ag+(aq) + Br–(aq) → AgBr(s)
4(b)[1]
(silver) nitrate
4(c)[1]
0.01 × 1000 / 50 = 0.2(00) (mol / dm3)
4(d)[1]
cream
4(e)[3]
M1 mol of AgBr = 0.01(00)
M2 Mr of AgBr = 188
M3 188 x 0.01 = 1.88 (g)
4(f)[1]
sodium ethanoate
4(g)(i)[1]
rinsing of residue
4(g)(ii)[1]
(crystals of) sodium ethanoate
4(h)(i)[2]
M1 named soluble barium salt e.g. barium chloride / barium nitrate
M2 named soluble sulfate salt e.g. sodium sulfate / potassium sulfate / ammonium sulfate / sulfuric acid
4(h)(ii)[2]
M1 any equation with BaSO4 as a product
M2 correct equation using soluble reactants
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