CALCULATION OF [H+]

1. [H+] is the molar concentration of Hydrogen ion in a solution (per liter).

2. Formula to calculate [H+] ion is pH= -log[H+]

3. Example : Calculate [H+] when pH is 6Solution : We know that pH = -log[H+][H+] = 10-pH

i.e., [H+] = 10-6 is the answer

CONCEPT OF MOLARITY

1. Molarity in other term is similar to concentration and is defined as the moles per unit volume.

2. There are two different formulas to calculate molarity.

3. M=(weight of solute/molecular weight)/ volume of solution in Liters

4. Initial conc. X initial Volume=final conc. X final volume i.e. M1V1 = M2V2

Q. What amount(volume) of acid is required to decrease the pH of a juice sample (100 Liters) from 5.2 to 3.2 ?

We know that pH= -log[H+]

[H+] = 10-pH i.e. [H+] = 10-5.2

[H+] = 6x10-6 i.e., this is the conc. (M1) when the pH of the juice is 5.2

[H+] = 10-3.2 [H+] = 4x10-4 i.e., this is the conc. (M2) when the pH of the juice is 3.2

We can calculate the required amount of acid to be added to the solutionM1 = 6x10-6 , V1 = 100M2 = 4x10-4 , V2 = ?

Now using the formula M1V1=M2V2 6x10-6 x 100 = 4x10-4 x v2

V2 = 1.5 Liter

CONCEPT OF PPM

ppm stands for parts per million i.e., 1 ppm= 1 ml in 10-6

ppm depends on concentration, temperature etc.

Q. What amount of Sodium Hypochlorite(NaOCl) is required to prepare 100 liters of a 50 ppm solution from a 12.5 percent sodium hypochlorite?

12.5 % of NaOCl solution means 12.5 in 100 units i.e., 12.5 in 102 units

1 unit = 12.5/102

106 unit = (12.5/102)x106 i.e., 125000 ppm Final chlorine solution volume = 100 Litres = 100,000

milliliters (ml)

We an calculate the required amount of NaOCl to be added

M1= 125000 ppm, V1= ? M2= 50 ppm , V2= 100,000 ml

Now using the formula M1V1=M2V2 125000 x V1 = 50 x 100,000

V1 = 40 ml