7.56 The pH of milk, black coffee, tomato juice, lemon juice and egg white are 6.8, 5.0, 4.2, 2.2 and 7.8 respectively. Calculate corresponding hydrogen ion concentration in each.

The hydrogen ion concentration in the given substances can be calculated by using the given relation: pH = –log [${\mathrm{H}}^{+}$]

(i) pH of milk = 6.8

Since, pH = –log [${\mathrm{H}}^{+}$]

6.8 = –log [${\mathrm{H}}^{+}$]

log[${\mathrm{H}}^{+}$] = –6.8

[${\mathrm{H}}^{+}$] = antilog(–6.8)

= 1.5×${19}^{-7}$ M

(ii) pH of black coffee = 5.0

Since, pH = –log [${\mathrm{H}}^{+}$]

5.0 = –log [${\mathrm{H}}^{+}$]

log[${\mathrm{H}}^{+}$] = –5.0

[${\mathrm{H}}^{+}$] = anitlog(–5.0)

${10}^{-5}$ M

(iii) pH of tomato juice = 4.2

Since, pH = –log [${\mathrm{H}}^{+}$]

4.2 = –log [${\mathrm{H}}^{+}$]

log[${\mathrm{H}}^{+}$] = –4.2 [H+] = anitlog(–4.2)

= 6.31× ${10}^{-5}$M

(iv) pH of lemon juice = 2.2

Since, pH = –log [${\mathrm{H}}^{+}$]

2.2 = –log [${\mathrm{H}}^{+}$]

log[${\mathrm{H}}^{+}$] = –2.2

[${\mathrm{H}}^{+}$] = anitlog(–2.2)

= 6.31× ${10}^{-3}$ M

(v) pH of egg white = 7.8

Since, pH = –log [${\mathrm{H}}^{+}$]

7.8 = –log [${\mathrm{H}}^{+}$]

log[${\mathrm{H}}^{+}$] = –7.8

[${\mathrm{H}}^{+}$] = anitlog(–7.8)

=1.58×${10}^{-8}$ M