OVERVIEW

• A 70% (w/w) Perchloric acid is a clear colorless aqueous solution of HClO₄. It can be purchased from many commercial suppliers.
• % refers to solution concentration in percentage and “(w/w)” refers to solute and solution amount given in grams (i.e., percent by weight). This means a 70% (w/w) Perchloric acid solution contains 70 g of HCLO₄ per 100 g of solution.
• The density of 70% Perchloric acid solution is 1.68 g/ml at 25° C. This means the weight of the 1 ml of 70% Perchloric acid solution is 1.68 grams at 25°C.
• Molarity refers to the number of moles of the solute present in 1 litre of solution. To calculate the molarity of 70% Perchloric acid solution, you need to know how many moles of HClO₄ are present in 1 liter of solution. 
• In simple words, 1 mole is equal to the molecular weight of the substance. For example, 1 mole of HCLO₄ is equal to 100.46 grams of HCLO₄ (molecular weight = 100.46).

Calculation procedure

Step 1: Calculate the volume of 100 grams of 70% Perchloric acid solution.
Formula:

Density = $\frac{Weight}{Volume}$

OR

Volume = $\frac{\mathrm{Weight}}{\mathrm{Density}}$

The volume of 100 g of 70% Perchloric acid solution : $\frac{100}{1.68}$ = 59.5238 ml

Note: A 70% (w/w) Perchloric acid means 100 grams of solution contains 70 grams of HCLO₄.

The volume of 100 grams of 70% Perchloric acid solution is 59.5238 ml. This means 70 grams of HCLO₄ is present in 59.5238 ml of 70% Perchloric acid solution.

Step 2: Calculate how many grams of HCLO₄ is present in 1000 ml of 70% Perchloric acid solution.

59.5238 ml of 70% Perchloric acid solution contains   = 70 grams of HClO₄
1 ml of 70% Perchloric acid solution will contain      =   $\frac{70}{59.5238}$ grams of HClO₄

1000 ml of 70% Perchloric acid solution will contain = $\frac{1000 x 70}{59.5238}$  = 1176.00 grams of HClO₄

1000 ml of 70% Perchloric acid solution will contain 1176.00 grams of HCLO₄.

Step 3: Calculate the number of moles of HCLO4 present in 1176.00 grams of HCLO4.

100.46 g of HClO₄ is equal to 1 mole.

1 g of HClO₄ will be equal to $\frac{1}{100.46}$ moles.

1176.00 grams of HCLO₄ will be equal to = $\frac{1176.00 \mathrm{x} 1}{100.46}$ = 11.706 moles

Therefore, we can say that 1 liter of 70% Perchloric acid solution contains 11.706 moles of HClO4 or in other words molarity of 70% (w/w) Perchloric acid is equal to 11.706M.