Question

The following two solutions are mixed: 100.0mL of 0.100M Na₂S, and 50.0mL of 0.100M FeCl₃.

a. Write a balanced chemical equation showing the proper phase for each product and reactant.

b. What is the molarity of each ion remaining in the solution, assuming complete precipitation of all insoluble compounds, and assuming that volumes are additive?

Answer 1

1.The balanced chemical equation is:

               3Na₂S(aq)    +    2FeCl₃(aq)                     ------------------->            6NaCl(aq) +   Fe₂S₃(s)

2.Ions that are remaining in the solution are:

Na+ and Cl-.

Their concentrations can be calculated as below:

                            3Na₂S(aq)    +    2FeCl₃(aq)                     ------------------->            6NaCl(aq) +   Fe₂S₃(s)

number of moles of each ion are:

0.1L x 0.100M x 6 of Na+= 0.06moles of Na+

0.05L x 0.100M x 6 of Cl-= 0.03moles of Cl-

molarity = number of moles/volume in litres

total volume = 100ml+50ml=150ml=0.15L

Hence molarity of Na+ ions = 0.06mol/0.15L

                                            = 0.4M

molarity of Cl- ions = 0.03mol/0.15L

                               = 0.2M