Question

You have hydrochloric acid with a concentration of 2,0 mol/L. How can you make a 100 mL solution with concentration of 0,50 mol/L HCl from this?

Answer 1

1. Find n(HCl) in 100 mL solution with concentration of 0,50 mol/L HCl:
1000mL of solution contains 0,50 mole of HCl;
100 mL of solution contains x mole of HCl;
1000/100 =0,50/x;
x = 0,05;
n(HCl) = 0,05 mole.
2. Find the volume of solution with concentration of 2,0 mol/L that contains 0,05 mole of HCl:
1000mL of solution contains 2,0 mole of HCl;
y mL of solution contains 0,05 mole of HCl;
1000/y = 2,0/0,05;
y = 25;
V(HCl) = 25 mL.
3. To get 100 mL solution with concentration of 0,50 mol/L HCl one needs to take 25 mL of solution with concentration 2,0 mol/L in 100 mL vessel and add necessary volume of water to reach 100 mL line.

To get 100 mL solution with concentration of 0,50 mol/L HCl one needs to take 25 mL of solution with concentration 2,0 mol/L in 100 mL vessel and add necessary volume of water to reach 100 mL line.