Question

HCl gas is in a 1.21-L cylinder at 0.870 atm and 28.0° C. This gas is dissolved in 750.0 mL of water. Calculate the pH of this solution (assume no volume change).

Answer 1

first find the moles of HCl

using PV = nRT formula

P = 0.87 atm , V = 1.21 L, R = 0.0821 L atm mol-1 K-1, T = 273+28 = 301 K

put these values in above equation

0.87 atm x 1.21 L = n x 0.0821 L atm mol-1 K-1 x 301

n = 1.0527 / 24.7121 mol-1

n = 0.0421 mol

given volume is 750 mL convert in to L = 0.75L

Molarity of HCl = moles / volume = 0.0421 mol / 0.75 L

= 0.0567 mol/L

since HCl is strong acid concentration of HCl = concentration of H+

pH = -logH+ = -log0.0567 = 1.24