## Ph Meter

Category : 10th Class

### Ph Meter

At 25°c temperature:

• If pH is greater than 7, the solution is basic
• If pH is equal to 7, the solution is neutral
• If pH is less than 7, the solution is acidic

In pure water:

$[{{H}^{+}}]=[O{{H}^{-}}]$

In acidic solution $[{{H}^{+}}]>[O{{H}^{-}}]$ and in basic solution $[{{H}^{+}}]<[O{{H}^{-}}]$

pH of some common samples

• Human blood (7.3-7.5)
• Soil alkaline (7-9)
• Wine (6.5 - 7.5)
• Cow's milk (4.8 - 8.4)
• Lemon Juice (6.3-6.6)
• Astric Juice (1 - 2) -

Importance of pH in Daily Life

• Aluminium hydroxide $[Al{{(OH)}_{3}}]$ is used for treatment of gastric ulcers.

The gastric ulcer is due to excessive secretion of hydrochloric acid in the stomach. The hydrochloric acid is secreted by stomach inner lining for digesting food. But its excessive secretion causes ulcer. Aluminium hydroxide is a base and it slowly neutralizes the excess of acid and gives relief to the patient.

• In Agriculture citrus crops grow better in alkaline soils, while sugarcane grow better in neutral soil.

The pH of soil is to be tested before growing the crop.

• In cosmetics - soaps, shampoos, creams etc are prepared with suitable pH for different types of skins.
• Tooth decay - When pH of our mouth reaches a value less than 5.5, the enamel of tooth starts-decaying. In presence of sugar and food particles in the mouth the bacterial action starts and acid is produced. This acid is naturalized by alkaline saliva in the mouth. The acid which is not neutralized can be removed by brushing with a tooth paste as they are alkaline and prevents the tooth decay.
• The sting of honey bee is very painful as it contains methanoic acid. To get relief, a milk solution of baking soda can be applied.

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