The hydrogen ion concentration in the given substances can be calculated by using the given relation: pH = –log [H+]

(i) pH of milk = 6.8 Since,

pH = –log [H+]

6.8 = –log [H+] log

[H+] = –6.8

[H+] = anitlog(–6.8)

= 1.5×19–7 M

(ii) pH of black coffee = 5.0 Since,

pH = –log

[H+] 5.0 = –log

[H+] log

[H+] = –5.0

[H+] = anitlog

(–5.0) = 10–5 M

(iii) pH of tomato juice = 4.2 Since,

pH = –log

[H+] 4.2 = –log

[H+] log

[H+] = –4.2

[H+] = anitlog

(–4.2) = 6.31×10–5 M

(iv) pH of lemon juice = 2.2 Since,

pH = –log

[H+] 2.2 = –log

[H+] log

[H+] = –2.2

[H+] = anitlog

(–2.2) = 6.31×10–3 M

(v) pH of egg white = 7.8 Since,

pH = –log

[H+] 7.8 = –log

[H+] log

[H+] = –7.8

[H+] = anitlog

(–7.8) =1.58×10–8 M