A 0.325 g sample of copper was weighed out by a student to start this experiment

Question

A 0.325 g sample of copper was weighed out by a student to start this experiment.

1. How many moles of Cu2+ ions should be produced when the nitric acid was added to the copper metal?

2.When the sodium hydroxide was added to the solution, how many moles of Cu(OH)2 should have formed?

3. The directions require you to add 1.00 g of zinc. If you assume a 100 % yield of copper, how many grams of zinc were added in excess?

4. If magnesium metal were used instead of zinc metal, what is the minimum mass, in grams, of magnesium metal that should be used to ensure that all of the copper ions in the solution is converted back to copper metal?

Explanation / Answer

1. Cu + 2HNO3 -> Cu(NO3)2 + H2 therefore no. of moles of Cu2+ ions produced = 0.325/ 63.5g = 0.005 mol 2. When the sodium hydroxide was added to the solution , Cu + 2NaOH -> Cu(OH)2 hence for one mole of Cu , 1 mol of Cu(OH)2 is formed. hence for 0.005 mol of Cu , 0.005mol of Cu(OH)2 is produced 3. mol wt of zinc = 64.5 g . Hence for 0.325 g of Cu , 0.33 g of zinc is required, but 1 g is added hence 0.67 g of zinc is added in excess 4. Mg mol wt = 24.3 g Hence Mg + Cu(OH)2 -> Cu + Mg(OH)2 Hence for forming 1 mol of Cu , 1 mol of Mg is required. hence for 0.005 mol , 0.1215g is required minimum

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