Find the mass of Hydrogen Chloride gas

Question

What mass of hydrogen chloride gas is required to produce 250 mL of a hydrochloric acid solution with a pH of 1.57?

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Answer 1

HCl(g) + H2O ==> HCl(aq)

pH = 1.57

[H+] = 1x10^-1.57 = 2.69x10^-2 M

Since we have 250 ml, this is equal to 0.250 L, so the moles of HCl needed would be ....

2.69x10^-2 mol/L x 0.250 L = 0.0067 moles HCl

Converting this to grams HCl using the molar mass of HCl, we have...

0.0067 moles HCl x 36.5 g / mol = 0.246 g HCl required (3 sig. figs.)