# Making HCl

## CAUTION!!

Wear eye protection, acid-resistant gloves, and an acid-resistant lab apron! When diluting concentrated acid, always add acid to water, never water to acid!!

I) Remember that percent concentration is always reckoned by weight.

II) You will need the percent concentration of the stock solution, and its density (specific gravity is numerically equal): 37.3%, and 1.189 g/ml, respectively for this example. These quantities are printed on the stock bottle label. The range of concentrations for stock HCl is commonly between 36.5% and 38.0%.

A) Take the reciprocal of the density (= 0.841 ml/g), and multiply by 100/100 (= 84.1 ml/100 g).

B) Use this information to convert [g HCl/100g sol'n] -- which you know as percent concentration -- to [ml HCl/g]:

Divide [84.1 ml/100g] by [37.3 g/100g] to find the number of milliliters of stock solution which contain 1 g of HCl; in this case it is 2.25 ml/g

III) 10% HCl has [10 g HCl/100 g sol'n], so use 10 g X 2.25 ml/g (= 22.5 ml) stock sol'n for every 100 ml of dilute acid desired. If you wish to make 1000 ml of 10% HCl, use 10 X 22.5 ml (= 225 ml) stock HCl.

IV) Add this amount to sufficient distilled/de-ionized water to the even 100 ml: 77.5 ml to make 100 ml of dilute acid, 775 ml to make 1000 ml.