Is it correct to say: Writing pH = log[H+] (missing negative sign)?

pH = -log[H+]. Without the minus, values become negative.

Is it correct to say: Saying 'acid + base → salt' (forgetting water)?

Complete equation is Acid + Base → Salt + Water. Water is always a product.

Is it correct to say: Confusing baking soda (NaHCO_3) with washing soda (Na_2CO_3·10H_2O)?

Baking soda is the mono-sodium salt; washing soda is the di-sodium salt with 10 water molecules of crystallisation.

Is it correct to say: Writing chlor-alkali products as only Cl_2 and NaOH?

Three products: NaOH (solution), Cl_2 (anode gas), H_2 (cathode gas).

Is it correct to say: Assuming all salts are neutral?

Salt of strong acid + weak base → acidic (NH_4Cl). Weak acid + strong base → basic (Na_2CO_3).

Is it correct to say: Adding water to concentrated acid?

Always add acid to water slowly with stirring. Reverse causes violent splashing due to heat of dilution.

Acids, Bases and Salts

Ionisation of acids/bases, pH scale, neutralisation, salt hydrolysis, chlor-alkali process — Maharashtra SSC Science Part 1

📐 12 formulas✏️ 3 examples🎯 6 practice⚖️ 4-5 marks🏫 Maharashtra State Board📚 Class 10✓ 2025–26 syllabus

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Board Exam Tips

→pH definition + one numerical (pH ↔ [H+]) is almost every year on SSC.
→Chlor-alkali process (electrolysis of brine) — memorise all three products and their uses.
→Marathi terms: आम्ल (acid), आम्लारी (base), क्षार (salt), उदासीनीकरण (neutralisation).
→Draw the pH-scale diagram with 4-5 examples (HCl, lemon, water, soap, NaOH) for a 2-mark question.
→State the colour change in indicators exactly (blue litmus → red in acid, phenolphthalein pink in base).

📐 Formulas(12)

Ionisation of an Acid

H C l \to H^{+} + C l^{-}

Ionisation of a Base

N a O H \to N a^{+} + O H^{-}

Neutralisation Reaction★ Board fav

Acid + Base \to Salt + Water

Definition of pH★ Board fav

p H = - lo g_{10} [H^{+}]

Symbol	Meaning
$[H^{+}]$	Molar concentration of H+ ions (mol/L)

pOH and its Relation

pO H = - lo g_{10} [O H^{-}], p H + pO H = 14

Ionic Product of Water

K_{w} = [H^{+}] [O H^{-}] = 1 0^{- 14} at 25 ° C

Acid + Metal

Z n + 2 H C l \to Z n C l_{2} + H_{2} ↑

Acid + Metal Carbonate

2 H C l + N a_{2} C O_{3} \to 2 N a C l + H_{2} O + C O_{2} ↑

Chlor-alkali Process★ Board fav

2 N a C l (a q) + 2 H_{2} O electrolysis 2 N a O H + C l_{2} ↑ + H_{2} ↑

Formation of Baking Soda (Solvay first step)

N a C l + H_{2} O + C O_{2} + N H_{3} \to N H_{4} C l + N a H C O_{3}

Formation of Washing Soda

2 N a H C O_{3} Δ N a_{2} C O_{3} + H_{2} O + C O_{2}

Bleaching Powder

C a (O H)_{2} + C l_{2} \to C a O C l_{2} + H_{2} O

✏️ Solved Examples

1Solved Exampleeasy2 steps

Calculate the pH of 0.01 M HCl solution.

HCl is a strong acid — dissociates completely

[H^{+}] = 0.01 = 1 0^{- 2} mol/L

2Solved Exampleboard4 steps

Write balanced equations for (a) Zn + dilute H_2SO_4, (b) NaOH + HCl. State the type of reaction in each.

Zinc displaces hydrogen from sulphuric acid

Z n + H_{2} S O_{4} \to Z n S O_{4} + H_{2} ↑

3Solved ExampleHOTS4 steps

The concentration of H+ ions in a solution is 4 × 10^-4 mol/L. Find its pH and state whether it is acidic, basic or neutral.

Substitute in pH formula

p H = - lo g (4 \times 1 0^{- 4})

⚠️ Traps & Common Mistakes

⚠️Common Mistakes6

1
Writing pH = log[H+] (missing negative sign)
✓pH = -log[H+]. Without the minus, values become negative.
2
Saying 'acid + base → salt' (forgetting water)
✓Complete equation is Acid + Base → Salt + Water. Water is always a product.
3
Confusing baking soda (NaHCO_3) with washing soda (Na_2CO_3·10H_2O)
✓Baking soda is the mono-sodium salt; washing soda is the di-sodium salt with 10 water molecules of crystallisation.
4
Writing chlor-alkali products as only Cl_2 and NaOH
✓Three products: NaOH (solution), Cl_2 (anode gas), H_2 (cathode gas).
5
Assuming all salts are neutral
✓Salt of strong acid + weak base → acidic (NH_4Cl). Weak acid + strong base → basic (Na_2CO_3).
6
Adding water to concentrated acid
✓Always add acid to water slowly with stirring. Reverse causes violent splashing due to heat of dilution.

🎯 Practice Yourself

🎯Practice Yourself6 questions

Q1
State the pH of pure water at 25 °C. What is its [H+]?
Q2
Name the acid present in curd, and its chemical formula.
Q3
Write the balanced reaction of dilute HCl with sodium bicarbonate.
Q4
List any two uses of bleaching powder (CaOCl_2).
Q5
The pH of a solution is 10. Find [H+] and [OH-].
Q6
Write the chemical formula of plaster of Paris and its precursor gypsum.

📝 Notes

Acids, Bases and Salts

Acids donate H+ ions, bases donate OH- ions, and their reaction produces salt + water. This chapter connects daily-life chemistry (curd, soap, antacids) with the industrial giants — chlor-alkali, baking soda and washing soda.

SSC angle

Maharashtra SSC weaves this chapter into Chemical Reactions (Ch 3) and Metallurgy (Ch 8):

2-mark: define acid/base, pH scale diagram, indicator colour changes.
3-mark: neutralisation with balanced equations, or a pH numerical.
HOTS: chlor-alkali flow chart with anode/cathode products.

Testing for acid or base

| Indicator | Acidic | Basic | |---|---|---| | Blue litmus | Turns red | No change | | Red litmus | No change | Turns blue | | Methyl orange | Red | Yellow | | Phenolphthalein | Colourless | Pink |

The pH scale

0-3: strong acids (HCl, H_2SO_4).
3-7: weak acids (vinegar, citric acid).
7: pure water — neutral.
7-11: weak bases (baking soda, ammonia).
11-14: strong bases (NaOH, KOH).

Salt families to remember

NaCl (common salt) — from HCl + NaOH.
NaHCO_3 (baking soda) — antacid, fire extinguisher, baking.
Na_2CO_3·10H_2O (washing soda) — cleaning agent, glass making.
CaOCl_2 (bleaching powder) — disinfectant, paper/textile bleach.
CaSO_4·½H_2O (Plaster of Paris) — from gypsum by heating at 373 K.

Board vs CBSE

Both boards teach identical content. Maharashtra SSC leans harder on real-life applications and preparation reactions of salts — practise writing every preparation equation.