Question

0.80 g of hydrogen chloride (hcl is dissolved in water to make 5.5 l of solution. what is the ph of the resulting hydrochloric acid solution?

Answer 1

HCl is a strong acid and so dissociates fully in water:
HCl(aq) --> H+(aq) + Cl-(aq)
Since there is a 1:1 mole ratio between HCl and H+ in this reaction, the number of moles of H+ = number of moles of HCl. The number of moles of HCl can be calculated as moles = mass/RMM = 0.80g / 36.5g/mol = 0.022mol.
Since 5.5 l  of solution is made, the concentration of H+ is:
[H+] = 0.022mol / 5.5l = 0.004M. This can then be used to calculate pH through the equation pH = -log[H+] = -log(0.004) = 2.40