Chemistry

Hydrogenionic Product (pH)


Where KW = H +. OH- and KW = 1.10-14, calculate the concentration value of H + ions and OH- ions:





So if 1.10-7 is the neutral solution, if there is more H + ions, the solution will be acidic. If there are more OH- ions, the solution will be basic.

Chemists have devised a simpler way to express these values. The concept of pH was used to calculate the amount of ions in these aqueous solutions.

pH is the hydrogenic product of water and is a scale designed to measure the acidity of aqueous solutions. pOH measures the amount of OH- ion in aqueous solutions.

See the scale made with the previously calculated values:

CONCENTRATION (mol / L)
1.10-14
1.10-7
1.10-1

TYPE OF SOLUTION
Basic
Neutral
Acidic

pH
14
7
1

The pH range ranges from 0 to 14. The logarithm is a function used to scale down. According to each pH, ​​there is a type of solution:

0  1  2  3  4  5  6

7

8  9  10  11  12  13  14

Acidic

Neutral

Basic

The determination of pH today is very important, such as in swimming pools, in an aquarium, in the soil, in a river, in our body, etc. It can determine if a solution is more acidic or more basic.

Look at the table with different pH values ​​found in our daily lives:

SYSTEM

pH at 25 ° C

Battery water

1,0

Gastric juice

1,6

Lemon juice

2,2-2,4

Vinegar

2,6-3,0

Orange juice

3,0-4,0

Wine

3,5

Beer

4,0

Acid rain

4,0

Coffee

5,0

Spittle

6,5

Cow milk

6,7

Pure water

7

Potable water

7,2

Blood and tear

7,4

Egg white

8,0

Sea water

8,0

Toothpaste

9,9

Soap

10,0

Milk of magnesia

10,5

Bleach

12,0

Green Devil Caustic Soda

14,0

Summing up:

Pure water

pH = 7

pOH = 7

Acid solution

pH <7

pOH> 7

Basic solution

pH> 7

pOH <7

Example:

- Calculate the pH of a 0.1mol / l NaOH solution.

                



pH + 1 = 14
pH = 14-1
pH = 13

Note that the same concentration of NaOH solution is the same concentration of OH- ions. POH is first calculated and then the pH.

- Calculate the pH of a 0.002mol / l HCl solution.


The concentration of the solution is equal to the concentration of H + ions.