Question

What is the amount of copper (Cu) in a sample of brass weighing 10.5 grams, if the sample was dissolved in sulfuric acid and the resulting Cu2+ ions were fully reduced using coulometry, requiring a total charge of 1150 C? (Assume 100% current efficiency and Faraday's constant as 96500 C/mol.)

Answer 1

To determine the amount of copper in the sample, we can use the following steps:1. Calculate the moles of electrons transferred during the reduction process.2. Determine the moles of copper reduced.3. Calculate the mass of copper in the sample.Step 1: Calculate the moles of electrons transferredTotal charge  Q  = 1150 CFaraday's constant  F  = 96500 C/molMoles of electrons  n  = Q / Fn = 1150 C / 96500 C/moln = 0.0119 mol of electronsStep 2: Determine the moles of copper reducedCopper ions  Cu2+  require 2 electrons to be reduced to copper metal  Cu :Cu2+ + 2e-  CuSo, the moles of copper reduced will be half the moles of electrons:Moles of Cu = 0.0119 mol of electrons / 2Moles of Cu = 0.00595 molStep 3: Calculate the mass of copper in the sampleThe molar mass of copper  Cu  is 63.55 g/mol.Mass of Cu = moles of Cu * molar mass of CuMass of Cu = 0.00595 mol * 63.55 g/molMass of Cu = 0.378 gTherefore, the amount of copper in the 10.5 g brass sample is approximately 0.378 g.