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.

Formula sheet (PDF) →

Chemistry · Chapter 5

Acids, Bases and Salts

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

12 formulas · 3 solved examples · 6 practice questions · Board weight: 4-5 marks · Maharashtra State Board Class 10

Not in the 2025–26 syllabus. This chapter is not part of the Maharashtra SSC (Std X) syllabus for 2025–26. It is kept here for reference.

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 ReactionBoard favourite

Acid + Base \to Salt + Water

Definition of pHBoard favourite

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 ProcessBoard favourite

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.