Question

Following are pH ranges for several human biological materials. From the pH at the midpoint of each range, calculate the corresponding [H3O+]. Which materials are acidic, which are basic, and which are neutral?

Gastric Contents, pH range 1.0-3.0

Saliva, pH range 6.5-7.5

Urine, pH range 4.8-8.4

Blood plasma, pH range 7.35-7.45

Answer 1

(i) For Gastric contents: pH range is 1.0 to 3.0

Mid point is 2.0

pH = 2.0

[H3O+] = 10^-pH = 10^-2.0 = 0.01 M

As it has pH less than 7, so it is acidic.

(ii) For Saliva: pH range is 6.5 to 7.5

Mid point is 7.0

pH = 7.0

[H3O+] = 10^-pH = 10^-7.0 = 10^-7 M

As it has pH = 7, so it is neutral.

(iii) For Urine: pH range is 4.8 to 8.4

Mid point is (4.8+8.4)/2 = 6.6

pH = 6.6

[H3O+] = 10^-pH = 10^-6.6 = 2.5*10^-7 M

As it has pH less than 7, so it is acidic.

(iv) For Blood Plasma: pH range is 7.35 to 7.45

Mid point is 7.40

pH = 7.40

[H3O+] = 10^-pH = 10^-7.40 = 4.0*10^-8 M

As it has pH more than 7, so it is basic.