Question

A 1.358g sample of brass is dissolved in nitric acid to produce 100.0 mL of a solution containing Cu2+ ions which are blue in solution. Using a colorimeter it is determined the molarity of the Cu2+ ions is 0.135M. What is the % of copper in the original brass sample?

Answer 1

To calculate the percentage of copper in the original brass sample using the molarity of Cu2+ ions, multiply the molarity of the solution by the volume to find moles of Cu2+, convert moles to mass, and divide the mass of copper by the mass of the brass sample and multiply by 100.

Step-by-step explanation:

The student is asking how to calculate the percentage of copper in the original brass sample, given the molarity of Cu2+ ions in a diluted solution. To find the percentage of copper, one needs to:

1. Calculate the number of moles of Cu2+ ions in the 100 mL solution using the molarity (0.135 M).
   
2. Determine the mass of Cu in grams from the number of moles, using copper's atomic mass (63.546 g/mol).
   
3. Divide the mass of copper by the mass of the brass sample and then multiply by 100 to find the percentage of copper.

To address the question step-by-step:

1. Calculate moles of Cu2+: Molarity (M) = moles of solute/volume of solution (L) => 0.135 mol/L * 0.100 L = 0.0135 moles of Cu2+.
   
2. Calculate mass of Cu: 0.0135 mol * 63.546 g/mol = 0.858 g of Cu.
   
3. Calculate percentage of Cu in brass: (0.858 g Cu / 1.358 g brass sample) * 100 = 63.2% Cu.