Question

A. If you have 100 mL of a 0.1 M solution of HCl and add 300 mL of distilled water, what will be the final molar concentration?

b. How much water should you add to a 50 ml 0.25 M NaOH solution to make a 0.05 M solution?

Answer 1

Answer: a) 0.00909 mol/L

b) 2g in litre

Step-by-step explanation: a) Given:

Volume = 100 ml = 100/1000 L = 0.1 L

Molarity = 0.1 M

Molarity = Mole / Volume

Mole = Molarity * Volume = 0.1 * 0.1 = 0.01 mol of HCl

1 L water is added,

now total volume = 0.1 + 1 = 1.1 L

Molarity = Mole / Volume = 0.01/1.1 =1/110 mol/L = 0.00909 mol/L

b) Compute the molar mass of NaOH by adding the atomic masses of the component atoms. 1 mole of Na has a mass of 23 g; 1 mole of oxygen has a mass of 16 g, and 1 mole of H has a mass of 1g. The masses sum up to 40g.

Multiply 40 g/ mole by 0.05 moles/liter. The product is 2 g/L.

Dissolve 2g of NaOH in a liter of water.

The resulting solution has a concentration of 0.05 M of NaOH or 0.05 moles per liter of NaOH