Reaction proportions?

Question

How would you tackle a question like this?

Q: What would be the minimum mass of silver Nitrate that would be needed to be added to 5g of Sodium Chloride to ensure complete precipitation of the chloride?

AgNo3(aq) + NaCl(aq) ---> AgCl(s) + NaNO3(aq)

Thank you very much

Answer 1

1. Number of moles of NaCl:  moles = mass/RFM

                                                     = 5.00/58.5

                                                     = 0.0855 (3s.f.)

2. AgNO3 and NaCl react in a 1:1 ratio therefore there are also 0.0855 moles of AgNO3

3. Mass of AgNO3: mass = moles x RFM

                                      = 0.0855 x 170

                                      = 14.5 g

Hope that makes sense!

Answer 2

1 mole of AgNO3 reacts with one mole of NaCl. So you divide the mass of NaCl by its molecular mass and find the number of moles. Then multiply this number of moles by the molecular mass of AgNO3 and find the required mass of AgNO3.