Question

what is the molarity of 20.0 ml of a KCl solution that reacts completely with 30.0 ml of a 0.400 M Pb(NO3)2 solution?

Answer 1

Answer:

[KCl] = 1.2 M

Explanation:

We need to complete the reaction:

2KCl(aq) + Pb(NO₃)₂(aq)  → 2KNO₃(aq) + PbCl₂(s)↓

By stoichiomety we know that 1 mol of chloride needs 1 mol of nitrate to react:

Let's find out the moles of nitrate, we have:

Molarity = mol/volume(L)

We convert the volume → 30 mL . 1L/1000mL = 0.030L

Molarity . volume(L) = moles → 0.400 M . 0.030L = 0.012 moles

Therefore, we can make a rule of three.

1 mol of nitrate reacts with 2 moles of chloride

Then, 0.012 moles of nitrate must react with (0.012 . 2) / 1 = 0.024 moles of KCl

We convert the volume from mL to L → 20 mL . 1L /1000mL = 0.020L

Molarity = mol /volume(L) → 0.024 mol /0.020L = 1.2 M