Question

For each reaction below, calculate the minimum amount of reactant needed to make the reaction go to completion. Identify each of the reaction below as precipitation, acid/base, or redox.

Start with 0.200g of Cu. 1. Cu(s) + 4HNO3(aq)  Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l) 0.200g Cu + x mL of 15.8M HNO3

2. Cu(NO3)2(aq) + 2NaOH(aq)  Cu(OH)2(s) + 2NaNO3(aq) x mL of 6.00M NaOH

3. Cu(OH)2(s) + H2SO4(aq)  CuSO4(aq) + 2H2O(l) x mL of 2.00M H2SO4

4. CuSO4(aq) + Mg(s)  Cu(s) + MgSO4 x g of Mg

After reaction 4 is complete there may be some Mg left over. Hydrochloric acid will be added to the solution.  Write the reaction for magnesium reacting with hydrochloric acid.  What kind of reaction is this?  Why does the HCl not react with the copper? (hint: activity series)

Answer 1

1. Cu(s) + 4 HNO₃(aq) ---------------------> Cu(NO₃)₂(aq) + 2 NO₂(g) + 2 H₂O(l)

0.2 gm Cu = 0.2 / 63.546 = 0.0031473 Moles

Hence amount of HCl =   0.0031473 x 1000 / 15.8 = 0.12 ml HCl is need.

This reaction gives 0.59 gm of Cu(NO₃)₂ for 100% yield.

2. Cu(NO₃)₂(aq) + 2 NaOH(aq) ----------------> Cu(OH)₂(s) + 2 NaNO₃(aq)

0.59 gm of Cu(NO₃)₂ = 0.59 / 187.5558 = 0.00314573 Moles

Volume of  6.00M NaOH need = 0.00314573 x 1000 / 6 = 0.524 ml of 6M NaOH need

This reaction will give 0.306899 gm of Cu(OH)₂

3. Cu(OH)₂(s) + H₂SO₄(aq) ----------> CuSO₄(aq) + 2 H₂O(l)

0.306899 gm of Cu(OH)₂ = 0.3068996 / 97.560 = 0.00314573 Moles

Volume of  2.00M H2SO4 need =   0.00314573 x 1000 / 2 = 1.572 ml of H2SO4 is need

This reaction will give 0.50208 gm of CuSO4

CuSO₄(aq) + Mg(s) --------------> Cu(s) + MgSO₄

0.50208 gm of CuSO4 = 0.50208 / 159.6086 = 0.00314569 Moles

Mg weight =  0.00314569 x 24.305 = 0.0764561 gm of Mg is need

reaction for magnesium reacting with hydrochloric acid

It is a exothermic reaction.

Mg + 2 HCl = MgCl₂ + H₂

Only those metals whose standard reduction potentials are lower than that of hydrogen react with non-oxidising acids like HCl and dil.H2SO4, and displace hydrogen from them.

Copper has higher reduction potential (more positive) than hydrogen, and it does not react with HCl acid.