2.3.2. pH Scale

We can quantitatively find the amount of these ions present in a solution? Can we judge how strong a given acid or base is?

We can do this by making use of a universal indicator, which is a mixture of several indicators. The universal indicator shows different colours at different concentrations of hydrogen ions in a solution. A scale for measuring hydrogen ion concentration in a solution, called pH scale has been developed. The p in pH stands for ‘potenz’ in German, meaning power.

The pH scale is a system that allows us to measure the acidity or basicity of a solution. When we talk about the power of hydrogen, we refer to the concentration of hydrogen ions (H⁺) in a solution. By using a universal indicator, which can change colors depending on the acidity or basicity, we can easily determine the pH value of various solutions.

Think of the pH scale like a measuring tape for how acidic or basic something is. Just like you can measure height, the pH scale allows us to measure acidity. For example, lemon juice is acidic, so it will have a low pH, while soap is basic and will have a high pH.

On the pH scale we can measure pH generally from 0 (very acidic) to 14 (very alkaline). pH should be thought of simply as a number which indicates the acidic or basic nature of a solution. Higher the hydronium ion concentration, lower is the pH value.

The pH of a neutral solution is 7. Values less than 7 on the pH scale represent an acidic solution. As the pH value increases from 7 to 14, it represents an increase in OH– ion concentration in the solution, that is, increase in the strength of alkali.

The pH scale ranges from 0 to 14. A pH of 7 is neutral, meaning that the solution is neither acidic nor basic. If the pH is less than 7, the solution is acidic, which means it has a higher concentration of hydrogen ions. Conversely, a pH greater than 7 indicates that the solution is basic (alkaline) and has a higher concentration of hydroxide ions.

Imagine a seesaw. At the center (pH 7), it is balanced (neutral). If one side goes down (pH < 7), it becomes acidic, while if the other side rises (pH > 7), it becomes basic. Just like that seesaw, the pH scale helps us balance our understanding of acids and bases.

Generally paper impregnated with the universal indicator is used for measuring pH.

Universal indicators are often found on pH test strips. When you dip these strips into a solution, they change color depending on the pH level of that solution. Each color corresponds to a specific pH value, making it easy to see how acidic or basic the solution is.

Using a pH test strip is like using a thermometer to check the temperature of water. Just as the thermometer tells you how hot or cold the water is, a pH strip tells you how acidic or basic the solution is by changing color.

The strength of acids and bases depends on the number of H+ ions and OH– ions produced, respectively. If we take hydrochloric acid and acetic acid of the same concentration, say one molar, then these produce different amounts of hydrogen ions. Acids that give rise to more H+ ions are said to be strong acids, and acids that give less H+ ions are said to be weak acids.

Different acids produce different amounts of H⁺ ions when dissolved in water. Strong acids, like hydrochloric acid, release a lot of H⁺ ions and thus are very effective at lowering the pH of a solution. Weak acids, like acetic acid (found in vinegar), release fewer H⁺ ions and have less effect on pH.

Think of strong and weak acids like a powerful speaker and a soft one. The powerful speaker (strong acid) can be heard from far away because they produce a loud sound (more H⁺ ions), while the softer speaker (weak acid) can only be heard nearby (fewer H⁺ ions).

Our body works within the pH range of 7.0 to 7.8. Living organisms can survive only in a narrow range of pH change. When pH of rainwater is less than 5.6, it is called acid rain. When acid rain flows into the rivers, it lowers the pH of the river water. The survival of aquatic life in such rivers becomes difficult.

Most living organisms need a specific pH range to thrive, typically between 7.0 and 7.8. If the pH of their environment falls outside this range, it can lead to health issues or even death. Acid rain is a concern because it can impact the natural pH levels of water bodies, harming fish and other aquatic life.

Imagine a fish tank. If the water's pH is too low or too high, the fish can get sick or die, just like how our body can react negatively if it doesn't maintain a suitable pH. Just as you would carefully check the water parameters for your fish, nature does the same for its aquatic organisms.

Plants require a specific pH range for their healthy growth. Our stomach produces hydrochloric acid. It helps in the digestion of food without harming the stomach. During indigestion the stomach produces too much acid and this causes pain and irritation. To get rid of this pain, people use bases called antacids.

Plants grow best in a certain pH range, which varies depending on the species. Similarly, our stomach uses hydrochloric acid for digestion, but too much acid can irritate the stomach lining. Antacids are bases that help neutralize excess stomach acid, relieving discomfort.

Just like how plants grow better in soil with the right pH, we need the right balance of stomach acid for digestion. When there's too much acid, it feels like a balloon that's about to burst! Antacids act like a gentle release valve, easing the pressure.

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