krit.club logo

Acids, Bases and Salts - Explain pH scale, neutralisation, and importance of pH in daily life

Grade 10CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

The pH scale is a scale for measuring hydrogen ion concentration, [H+][H^+], in a solution.

•

The 'p' in pH stands for 'potenz' in German, which means power.

•

The pH scale ranges from 00 (very acidic) to 1414 (very alkaline/basic).

•

A neutral solution has a pH=7pH = 7. Examples include pure H2OH_2O and NaClNaCl solution.

•

Acidic solutions have a pH<7pH < 7. The lower the pH value, the higher the concentration of H+H^+ (or H3O+H_3O^+) ions.

•

Basic solutions have a pH>7pH > 7. The higher the pH value, the higher the concentration of OH−OH^- ions and lower the concentration of H+H^+ ions.

•

The strength of acids and bases depends on the number of H+H^+ ions and OH−OH^- ions produced, respectively. Strong acids like HClHCl dissociate completely, while weak acids like CH3COOHCH_3COOH dissociate partially.

•

Universal Indicator is used to determine pH by showing different colors at different concentrations of hydrogen ions in a solution.

•

Importance of pH in daily life: Plants and animals are pH sensitive. Our body works within the pH range of 7.07.0 to 7.87.8. Acid rain has a pH less than 5.65.6.

•

pH in the digestive system: The stomach produces HClHCl with a pH of about 1.21.2. Excess acid causes indigestion, which is treated with antacids like Mg(OH)2Mg(OH)_2 (Milk of Magnesia).

•

Tooth decay starts when the pH of the mouth is lower than 5.55.5. Bacteria produce acids by degradation of sugar and food particles.

📐Formulae

pH=−log⁡10[H+]pH = -\log_{10}[H^+]

[H+][OH−]=10−14 at 25∘C[H^+][OH^-] = 10^{-14} \text{ at } 25^\circ C

If [H+]=10−x, then pH=x\text{If } [H^+] = 10^{-x}, \text{ then } pH = x

pH+pOH=14pH + pOH = 14

💡Examples

Problem 1:

You have two solutions, A and B. The pH of solution A is 66 and the pH of solution B is 88. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic?

Solution:

Solution A (pH=6pH = 6) has a higher hydrogen ion concentration than solution B (pH=8pH = 8). Solution A is acidic and solution B is basic.

Explanation:

On the pH scale, values less than 77 represent acidic nature and values greater than 77 represent basic nature. Since pHpH is the negative logarithm of [H+][H^+], a lower pH value indicates a higher concentration of H+H^+ ions. Solution A has [H+]=10−6 mol/L[H^+] = 10^{-6} \text{ mol/L} while Solution B has [H+]=10−8 mol/L[H^+] = 10^{-8} \text{ mol/L}.

Problem 2:

Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4,1,11,74, 1, 11, 7 and 99 respectively. Which solution is: (a) neutral (b) strongly alkaline (c) strongly acidic (d) weakly acidic (e) weakly alkaline?

Solution:

(a) D (pH=7pH = 7), (b) C (pH=11pH = 11), (c) B (pH=1pH = 1), (d) A (pH=4pH = 4), (e) E (pH=9pH = 9).

Explanation:

According to the pH scale: pH=7pH = 7 is neutral. pH=1pH = 1 is the lowest value here, making it strongly acidic. pH=11pH = 11 is the highest, making it strongly alkaline. pH=4pH = 4 is closer to neutral than 11, so it is weakly acidic. pH=9pH = 9 is closer to neutral than 1111, so it is weakly alkaline.

Problem 3:

A milkman adds a very small amount of baking soda (NaHCO3NaHCO_3) to fresh milk. Why does he shift the pH of the fresh milk from 66 to slightly alkaline?

Solution:

He shifts the pH to prevent the milk from setting as curd quickly.

Explanation:

Fresh milk has a pH of 66 and is slightly acidic. As it sits, bacteria produce lactic acid, which lowers the pH and causes the milk to curdle. By adding baking soda (NaHCO3NaHCO_3), which is basic, the milkman increases the pH (making it alkaline). This alkaline environment neutralizes the lactic acid produced, delaying the souring and curdling process.

Explain pH scale, neutralisation, and importance of pH in daily life Class 10 Notes & Examples