Mass calculations
\(copper\:sulfate + sodium\:hydroxide \rightarrow copper\:hydroxide + sodium\: sulfate\)
The solid copper hydroxide precipitate was collected by filtering, washed with water and dried in an oven. It was found to weigh 1.95g and from this we can calculate the mass of copper sulfate in solution at the start
\(CuSO_{4} + 2NaOH \rightarrow Cu(OH)_{2} + Na_{2}SO_{4}\)
Step 1 - Work out the number of moles of copper hydroxide that were collected.
\(Number of moles of precipitate (Cu(OH)_{2}) = \frac{mass\:of\:Cu(OH)_{2}}{formula\: mass\:of\:Cu(OH)_{2}}\)
\(= \frac{1.95}{97.5} = 0.02\:moles\)
Step 2 - Find the mole ratio
\(CuSO_{4} + 2NaOH \rightarrow Cu(OH)_{2} + Na_{2}SO_{4}\)
Using the balanced equation we can see that 1 mole of \(CuSO_{4}\) makes 1 mole of \(Cu(OH)_{2}\) looking at the large balancing numbers. The mole ratio is 1:1.
From step 1 we know that there were 0.02 moles of \(Cu(OH)_{2}\) so there must have been 0.02 moles of \(CuSO_{4}\) in the solution at the start.
Step 3 - Calculate the mass
Using the same formula as step 1
\(mass = number\: of\: moles \times formula\: mass\) \(mass\: of\: CuSO_{4} = 0.02 \times 159.5\) \(= 3.19g\)
There was therefore 3.19g of \(CuSO_{4}\) in the solution at the start.
