pH: Definition, Uses and Facts

pH in Chemistry is used to measure the acidity or basicity of an aqueous solution. The full form of pH is the Potential of Hydrogen. It is the negative logarithm H+ion concentration. Students can measure the pH value by using a pH scale. The pH scale ranges from 0 to 14 in water. pH 7 is neutral. Solutions carrying the pH value from 0 to 7 come under the acidic state, whereas 8 to 14 are basic.

According to the research, pH is very important for water purification, chemistry, medicines, biology, agriculture, and other science-related activities. Scroll down to read more on pH!

Definition and Fullform of pH

The pH of a solution can be defined as the negative logarithm of its \(\left( {{{\rm{H}}^ + }} \right)\) ion concentration.,
\({\rm{pH}} = \; – {\rm{log}}\left( {{{\rm{H}}^ + }} \right)\)
The pH of a solution is also defined as the logarithm of the reciprocal of \(\left( {{{\rm{H}}^ + }} \right)\) ion concentration.
\({\rm{pH}} = {\rm{log}}\;1/\left( {{{\rm{H}}^ + }} \right)\)

pH is an abbreviation for “power of hydrogen” where “p” is short for the potenz (the German word for power), and H is the symbol of the element hydrogen. 

pH Scale in Chemistry

A litmus solution or litmus paper determines whether a given solution is acidic or basic. But suppose you have two acidic solutions containing different amounts of acids in them. We cannot say which solution is more acidic than the other. Similar is the case with the basic solutions. This problem is solved by using a scale known as the pH scale.

Who Discovered the pH Scale?

the pH scale is introduced by S.P.L. Sorensen in \( 1909.\) pH of a solution indicates which solution is more acidic or more basic than the other.
Sorensen linked the hydrogen ion concentrations of acid and base solutions to the simple numbers \(0\) to \(14\) on his pH scale. The pH of a solution is inversely proportional to the concentration of hydrogen ions in it. That is, a solution having a high concentration of hydrogen ions has a low pH value. On the other hand, a solution having a low concentration of hydrogen ions has a high pH value. Thus the strength of an acid or base is measured on a scale of numbers called the pH scale.

Learn About Acids and Bases

pH of Acids and Bases

Here, we have mentioned some of the most important rules while using the pH scale. Students must go through the pointers given below to know more about the same.

1. Neutral Substances have a pH of Exactly \(7\): The neutral solutions have pH \(7.\) Pure water is a neutral substance. So, the pH of pure water is \(7.\) A substance having pH \(7\) will have no effect on the litmus paper or any other common indicators such as methyl orange or phenolphthalein, etc.
   
2. Acids have a pH of Less than \(7\): A solution with a pH of less than \(7\) is an acidic solution. For example, a solution with a pH of \(4\) will be acidic in nature. A solution of pH \(1\) is much more acidic than another solution of pH \(4.\) In other words, a solution of pH \(1\) will be a much stronger acid than another acid having pH \(4.\) The solutions with pH of \(0,{\rm{ }}1,{\rm{ }}2,{\rm{ }}3\) are usually considered strong acids, and the solutions with pH of \(4,{\rm{ }}5,{\rm{ }}6\) are considered weak acid solutions. The solutions with pH less than \(7\) are acidic in nature, and hence they turn blue litmus to red. They also turn methyl orange indicator red.
   
3. Bases have a pH of more than \(7\): A solution with a pH of more than \(7\) is a basic solution or alkaline solution. For example, a solution with a pH of \(11\) will be basic in nature. A solution of pH \(14\) will be much more basic than another solution of pH \(10\). In other words, a solution of pH \(14\) will be a much stronger base than another solution of pH \(10.\) The solutions with pH values of \(8,{\rm{ }}9,\) and \(10\) are usually considered weak bases, and the solutions with pH values of \(11,{\rm{ }}12,{\rm{ }}13,\) and \(14\) are usually considered strong bases. All the substances having a pH of more than \(7\) are basic in nature, and hence they turn red litmus to blue. They also turn phenolphthalein indicator pink.

pH Values Of Some Of The Common Substances

How to Measure pH?

The pH of a solution is generally determined with the help of a pH paper or universal indicator. The pH paper gives a particular colour with a solution of particular pH. The colour is compared with a chart with different colours at different pH values.

The pH Of A Solution Can Be Measured in Two ways:

1. Adding universal indicator solution or paper to the solution and reading the pH from the colour chart for the indicator
2. Reading from a pH meter with the probe dipped into the solution.

Universal Indicator

Common acid-base indicators indicate whether a solution is acidic or basic. They cannot be utilized for determining the strength of acidic or alkaline solutions. They cannot differentiate between acidic or basic solutions of different pH values. 
For example, litmus can tell us that sulphuric acid and vinegar are both acidic, but it cannot be said that sulphuric acid is stronger than vinegar.
“A universal indicator is a mixture of several indicators. The universal indicator shows different colours at different concentrations of hydrogen ions in a solution”.

Utility Of Universal Indicator:

1. It indicates the strength or pH range of the acidic or alkaline solution.
2. It can be utilized for determining the strength of acidic or alkaline solutions.
3. It can differentiate between acidic or basic solutions of different pH values by giving different colours with different pH values.

Colour Change by Universal Indicator: The universal indicator is used in a solution or a paper strip impregnated with the universal indicator called the pH paper.

• A drop of the solution to be tested is put on a strip of universal indicator paper.
• The indicator paper change in colour.
• The colour produced on the indicator paper is then matched on the standard pH colour chart.
• We can read the pH value corresponding to this colour from the colour chart.
• After knowing the pH value, we can tell whether the acid or base is strong or weak.

pH Meter

The pH paper gives only approximate values of the pH of the solution. Nowadays, the pH of a solution can be measured accurately with the help of a pH meter.

Effect of Temperature and Concentration on pH Change

Effect of Temperature on pH: Increasing temperature decreases the pH of the aqueous solution

Effect of Concentration: If \(\left( {{{\rm{H}}^ + }} \right)\) concentration increases by \(10\) times pH decreases by \(1\) unit, and if \(\left( {{{\rm{H}}^{\rm{ + }}}} \right)\) concentration decreases by \(10\) times, the pH increases by \(1\) unit.

1. In general, if the changing factor of \(\left( {{{\rm{H}}^ + }} \right)\) is m, the change in units of pH is \({\rm{lo}}{{\rm{g}}_{10}}{\rm{m}}{\rm{.}}\)
2. In general, if pH changes by p units, then changing factor of \(\left( {{{\rm{H}}^ + }} \right)\) is \(\left({{{10}^{\rm{p}}}} \right).\)

Importance of pH in Everyday Life

Let’s understand the importance of pH in our daily life through some examples:

Are Plants And Animals pH-Sensitive?

All plants and animals are pH-sensitive. Living organisms work within a narrow range of pH like our body also works within the pH range of \(7.0\) to \(7.8.\) If this pH range increases or decreases, the survival of living organisms becomes difficult.

For Example

1. We face the problem of acidity when the pH of our stomach decreases.
2. If the pH value of our mouth decreases, our tooth starts decaying.
3. During the stinging by a bee or wasp, the pH of our skin changes that causes irritation and pain.
4. If the pH value of river water decreases, the survival of aquatic life becomes difficult.
5. If the pH value of the soil increases or decreases, then the normal soil becomes infertile. Hence, it is clear that living organisms are pH-sensitive.

pH in Our Digestive System

When we eat food, digestion starts in our mouth, where salivary amylase acts on carbohydrates. It works under optimum pH of \(6.7-7.0.\) In the stomach, the presence of gastric juices makes the medium acidic, killing many harmful microorganisms that might have been swallowed along with the food.

The enzyme pepsin in the stomach works best in an acidic medium (at pH around \(2\)). From the stomach, food travels to the small intestine. The enzymes in the small intestine like peptidase, trypsin, and maltase work best in an alkaline medium (at a pH of around \(7.5\)). Bile juice makes the medium alkaline in the small intestine.

Tooth Decay as A Result of pH Change

A balanced pH protects dental health, and this may be done by focusing on the alkaline diet. Cleaning the mouth thoroughly by rinsing with plenty of water after eating food also reduces the risk of cavities, gum disease, and tooth decay. Toothpaste being basic in nature neutralizes acid in our mouth and helps in preventing tooth decay. Foods such as candies, sweets, ice cream, and chocolates should be consumed less to maintain a balanced pH.

pH of Soil

Soils are generally acidic. Plants require a definite pH range for their proper growth. They do not grow in alkaline soil, and many plants do not grow properly in highly acidic or highly alkaline soil. So, highly acidic soil is treated by spreading quicklime, slaked lime, or calcium carbonate to lower its acidity.

FAQs

Here, we have enlisted some of the most important frequently asked questions related to pH and its scale. Candidates must read these questions and answers to clear out their doubts regarding the same subject.

Q.1. What is high pH called?
Ans: A solution of a high pH value (pH value with more than \(7\)) has a higher concentration of hydroxide ions than the hydronium ions and hence, is called a base.

Q2. Who introduced the concept of pH to measure the strength of acids and bases?
Ans: “pH” was first introduced by Danish biochemist Soren Peter Lauritz Sorensen in \(1909.\)

Q.3. What is the name of the indicator which can be used for testing the pH of a solution?
Ans: The name of the indicator which can be used for testing the pH of a solution is a universal indicator.

Q.4. What is the importance of pH?
Ans:
a. pH control is essential for the optimum growth of plants.
b. Biological processes take place at optimum pH.
c. Many industrial processes require control of pH.
d. Medicinal preparation such as injections, syrups requires control of pH for further stability.

Q.5: Is pH \(0\) or pH \(14\) possible?
Ans: The pH of a solution is inversely proportional to the concentration of hydrogen ions in it. That is, a solution having a high concentration of hydrogen ions has a low pH value. On the other hand, a solution having a low concentration of hydrogen ions has a high pH value. so, it is not possible to have a pH above \(14\) or below zero.

Q.6. What is the pH of pure water at \(25^\circ \,{\rm{C}}\)

Ans: The pH of pure water at \(25^\circ \,{\rm{C}}\) is \(7.\) The temperature increases, ionisation of water increases, however the concentration of \(\left( {{{\rm{H}}^ + }} \right)\) ions and \(\left( {{\rm{O}}{{\rm{H}}^ – }} \right)\) ions are equal.

Q.7. What is the highest pH level?
Ans: The pH level ranges from \(0\) to \(14.\) Hence, the highest pH level is \(14.\)

Q.8. What is the pH value of acid rain?
Ans: pH of rain is around \(5.6\) which is due to the presence of carbonic acid in it. But when the pH of rain is less than \(5.6\), it is referred to as acid rain. This acid rain decreases the pH of water in lakes and rivers. This adversely affects the life of aquatic animals and plants. Some aquatic animals and plants die due to acid rain and some plants lose their leaves.

Q.9. What is the pH formula?
Ans: The formula of pH is \({\rm{pH}} = – {\rm{log}}\left( {{{\rm{H}}^ + }} \right).\)

Q.10. What is pH and why is it important?
Ans: The pH is the power of hydrogen ions. The nature of a solution can be determined based on Hydrogen ion concentration.
pH is important for living organisms. They can survive only in a narrow range of pH changes. Our body works within the pH range of \(7.0\) to \(7.8.\) When the pH of rainwater is less than \(5.6\), it is called acid rain and if the pH value of river water decreases, survival of aquatic life becomes difficult. Hence, pH value has a lot of real-life applications.

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Study Materials on Embibe

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From this article, we understood that pH helps us test the acidity and basicity of a solution. We also got to know that pH plays an important role in many activities of our daily life. So, It is important for us to assist our body in creating and maintaining a healthy pH since most diseases, illnesses, and bad bacteria thrive in an over-acidic environment.

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PRACTICE QUESTIONS ON pH

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