Brass is an alloy of copper and zinc. An experiment is completed to find the percentage by mass of copper in a sample of brass. In the experiment, the sample of brass is reacted with an excess of concentrated nitric acid, HNO3. This forms a solution containing Cu2+(aq) ions. The amount of Cu2+(aq) ions formed is determined by titration. A student uses the following method. step 1 Weigh a glass beaker and record the mass. step 2 Add approximately 1.00g of powdered brass to the beaker and record the mass of the beaker and the brass. step 3 Transfer the brass into conical flask A which contains excess concentrated HNO3. step 4 Reweigh the glass beaker and record the mass. step 5 Add aqueous sodium carbonate, Na2CO3(aq), dropwise to flask A until a precipitate of copper(II) carbonate, CuCO3(s), appears. Then add dilute ethanoic acid dropwise until the precipitate is fully dissolved. step 6 Transfer all the contents of flask A to a 100.0cm³ volumetric flask and make up to the mark with distilled water. This is solution B. step 7 Transfer 10.0 cm³ of solution B into conical flask C. step 8 Add 10cm³, an excess, of aqueous potassium iodide, KI(aq), to flask C. step 9 Titrate the contents of flask C against 0.0600moldm⁻³ sodium thiosulfate, Na2S2O3(aq), using starch solution as an indicator. step 10 Repeat steps 7 to 9 until concordant results are obtained.