10 Introductory Chemistry 2017/18 H8IICH Part C (50 marks) Calculation of the Mo

Question

10 Introductory Chemistry 2017/18 H8IICH Part C (50 marks) Calculation of the Molarity of copper in the "Brass Contaminated Sand (BCS) solution" and the calculation of the % w/w copper of the brass in the Brass Contaminated Sand (BCS) solid Given that the zinc ions in the Brass Contaminated Sand (BCS)' solution do not react with thiosulphate and can be considered as spectator ions. Assume that the reaction between copper ions and thiosulphate ions is a 1 to 1 reaction. Note: The assumption is a correct statement but is an over-simplification of the overall reaction. The assumption is given to allow you to undertake the calculation without knowledge of the reaction Calculate the Molarity of copper in the 'Brass Contaminated Sand (BCS)' solution and quote your answer to 4 decimal places. ( Molarity of Na2S203.5H20 0.07999 M and the Volume 25ml,20 ml of Brass contaminated sand used And Calculate the % w/w of copper in the brass component of the Brass Contaminated Sand (BCS) solid and quote your answer to 2 decimal placesA sample of Brass Contaminated Sand (BCS) from the fly tip site is found to contain 3.87 % w/w brass and has been quantitatively prepared for you by weighing accurately 1280.8199 gram of Brass Cortamiriated Sand (BCS

Explanation / Answer

1) M1=molarity of BCS=?

V1=volume of BCS=20ml

M2=molarity of thiosulfate=0.07999M

V2=volume of thiosulfate=25ml

Copper and thiosulfate reacts in 1:1 molar ratio

mol of Cu=M1V1 is equal to mol of thiosulfate=M2V2

M1V1=M2V2

or, M1=M2V2/V1=(0.07999M)(25ml/20ml)=0.09999M

M1=0.09999M

2) M1=molarity of Copper in BCS=0.0999mol/L

mass of copper in BCS solution=M1*molar mass(Cu)=0.09999mol/L*(63.546g/mol)=6.35396 g/L=6.35396g/1000g water [density of water=1g/ml)

%(w/w) of Cu in the solution=(6.353960g/1000g)*100=0.63%

%(w/w) brass in the solution=3.87%

thus %(w/w) of Cu in brass=(0.63/3.87)*100=16.28%

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