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pH
pH full form is "potential of hydrogen" (or "power of hydrogen").
pH is a scale used to specify the acidity or basicity of an aqueous solution.
Acidic solutions (solutions with higher concentrations of H+ ions) are measured to have lower pH values than basic or alkaline solutions.
The pH scale ranges from 0 to 14.
The pH scale is logarithmic and inversely indicates the concentration of hydrogen ions in the solution.
pH=−log10[H+]
If pH < 7 → acidic solution (At 25 °C (77°F), solutions with a pH less than 7 are acidic)
If pH > 7→ basic solution (At 25 °C (77°F), solutions with a pH greater than 7 are basic)
If pH = 7→ neutral solution (At 25 °C (77°F), Solutions with a pH of equal 7 are neutral)
Pure water have the same concentration of H+ ions as OH- ions.
The neutral value of the pH depends on the temperature
The pH value can be less than 0 for very concentrated strong acids, or greater than 14 for very concentrated strong bases.
The pH value can be less than 0 for very concentrated strong acids, or greater than 14 for very concentrated strong bases.
Primary pH standard values are determined using a concentration cell with transference, by measuring the potential difference between a hydrogen electrode and a standard electrode such as the silver chloride electrode.
The pH of aqueous solutions can be measured with a glass electrode and a pH meter, or a color-changing indicator.
Pure water is neutral. When an acid is dissolved in water, the pH will be less than 7 (25 °C). When a base, or alkali, is dissolved in water, the pH will be greater than 7. A solution of a strong acid, such as hydrochloric acid, at concentration 1 mol dm^(−3) has a pH of 0. A solution of a strong alkali, such as sodium hydroxide, at concentration 1 mol dm^(−3), has a pH of 14.
Method of measuring pH is using an Indicators and an electronic pH meter. For More precise measurements the color can be measured spectrophotometrically, using a colorimeter or spectrophotometer.
pOH is sometimes used as a measure of the concentration of hydroxide ions, OH−.
pH of salts
A salt of a strong acid and a strong base will be neutral in nature. pH = 7 (approx.).
A salt of a weak acid and a strong base will be basic in nature. pH > 7.
A salt of a strong acid and a weak base will be acidic in nature. pH < 7.
The pH of a salt of a weak acid and a weak base is determined by conducting a pH test.
pH scale
The pH scale ranges from 0 to 14.
Importance of pH in everyday life
1. pH sensitivity of plants and animals
Plants and animals are sensitive to pH. Crucial life processes such as digestion of food, functions of enzymes and hormones happen at a certain pH value.
2. pH of a soil
The pH of a soil optimal for the growth of plants or crops is 6.5 to 7.0.
3. pH in the digestive system
The process of digestion happens at a specific pH in our stomach which is 1.5 to 4.
The pH of the interaction of enzymes, while food is being digested, is influenced by HCl in our stomach.
4. pH in tooth decay
Tooth decay happens when the teeth are exposed to an acidic environment of pH 5.5 and below.
5. pH of self-defense by animals and plants
Acidic substances are used by animals and plants as a self-defense mechanism. For example, bee and plants like nettle secrete a highly acidic substance for self-defense. These secreted acidic substances have a specific pH.
pH of different Compounds and Solutions
pH of battery acid < 1
pH of battery acid < 1
pH of Gastric acid 1.0 – 1.5
pH of Vinegar 2.5
pH of Orange juice 3.3 – 4.2
pH of Black coffee 5 – 5.03
pH of Milk 6.5 – 6.8
pH of Pure water 7
pH of Sea water 7.5 – 8.4
pH of Ammonia 11.0 – 11.5
pH of Bleach 12.5
pH of Lye 13.0 – 13.6
pH of Gastric acid 1.5–3.5
pH of Lysosomes 4.5
pH of Human skin 4.7
pH of Urine 6.0
pH of Cytosol 7.2
pH of Blood (natural pH) 7.34–7.45
pH of Cerebrospinal fluid (CSF) 7.5
pH of Mitochondrial matrix 7.5
pH of Pancreas secretions 8.1
pH of Granules of chromaffin cells 5.5