We can calculate the hydrogen ion concentration by applying the formula, pH = –log [H+]

(i) pH of milk = 6.8

Since, pH = –log [H+]

⇒6.8 = –log [H+]

⇒log [H+] = –6.8

By taking antilog of both the sides, we get

⇒[H+] = antilog (–6.8)

⇒[H⁺]= 1.5×19–7 M

(ii) pH of black coffee = 5.0

Since, pH = –log [H⁺]

⇒5.0 = –log [H⁺]

⇒log [H⁺] = –5.0

By taking antilog of both the sides, we get

⇒[H⁺] = antilog (–5.0)

⇒[H⁺] = 10^-5 M

(iii) pH of tomato juice = 4.2

Since, pH = –log [H⁺]

⇒4.2 = –log [H⁺]

⇒log [H⁺] = –4.2

By taking antilog of both the sides, we get

⇒[H⁺] = antilog (–4.2)

⇒[H⁺]= 6.31×10^-5 M

(iv) pH of lemon juice = 2.2

Since, pH = –log [H⁺]

⇒2.2 = –log [H⁺]

⇒log [H+] = –2.2

By taking antilog of both the sides, we get

⇒[H⁺] = antilog (–2.2)

⇒[H⁺]= 6.31×10^-3 M

(v) pH of egg white = 7.8

Since, pH = –log [H⁺]

⇒7.8 = –log [H⁺]

⇒log [H⁺] = –7.8

By taking antilog of both the sides, we get

⇒[H⁺] = antilog (–7.8)

⇒[H⁺]=1.58×10^-8 M