Class 10 Science · Original EZT practice
Acids, Bases and Salts (Class 10 Chapter 2): summary and practice
Acids, Bases and Salts is the lab-bench chapter: what indicators show, how acids and bases react with metals, carbonates, oxides and each other, why water unlocks H+ and OH-, what the pH scale measures, and how salt families and their crystals behave. All questions are original EZT tutor practice following the chapter's own section order.
6 original worked examples, 6 fresh self-check questions and 4 mixed questions, with explained answers. These are not copied textbook exercises, an official chapter index or a full answer key. No affiliation with NCERT is claimed.
Official sources for topic and edition context, checked 21 October 2026:
1. Acids and bases in the laboratory
Indicators translate chemistry into colour: litmus flips red-blue, turmeric stays yellow in acid and turns reddish in base, and olfactory indicators like onion and vanilla lose their smell in base but not in acid. Section 2.1.1 runs these tests.
2. Characteristic reactions
Acids release hydrogen with active metals, carbon dioxide from carbonates and hydrogencarbonates, and water when they meet a base - neutralisation. Metallic oxides behave like bases toward acids, while non-metallic oxides behave like acids toward bases: sections 2.1.2 to 2.1.6 with their word equations.
3. What acids and bases share in water
Acids produce H+ (as H3O+) and bases produce OH- only in water - dry HCl gas is not acidic at all. Diluting is exothermic, so always add acid to water with stirring, never the reverse.
4. The pH scale
pH counts hydrogen-ion concentration on a 0 to 14 scale: 7 is neutral, below is acidic, above is basic. Section 2.3.1 applies it to everyday life - soil for crops, stomach acid, toothpaste against decay.
5. More about salts
Salts sort into families by their parent acid and base, and their own pH follows the stronger parent. From common salt come chlor-alkali products like NaOH, bleaching powder, baking soda and washing soda, and many salt crystals carry water of crystallisation.
Choose, solve, check, then try a fresh question.
Before calculating, read the method prompt and name the condition that makes it useful. Write your own attempt. Open the steps only when you need them, and use the check to catch a wrong sign, unit or interpretation. Finish with the fresh question before reading its answer.
pH of a strong acid
Choose the method: pH = -log[H+]; a strong acid dissociates fully.
EZT practice question
Find the pH of 0.01 M HCl, a strong acid.
Show the worked solution
- Full dissociation, so [H+] = 0.01 = 10^-2 M.
- pH = -log(10^-2).
Answer: pH = 2 - strongly acidic.
Check: Ten times more dilute means one pH unit up: 0.001 M HCl sits at pH 3.
Watch for this: Strong versus concentrated are different words - strength is about dissociation, concentration about amount per litre.
Now try it yourself
pH of 0.001 M HCl?
Check your answer
3.
[H+] = 10^-3, so pH = 3.
Read pH from [H+]
Choose the method: pH is the negative log of the hydrogen-ion concentration.
EZT practice question
A solution has [H+] = 10^-4 mol/L. Find its pH and say whether it is acidic or basic.
Show the worked solution
- pH = -log(10^-4) = 4.
- Below 7 on the scale.
Answer: pH 4, acidic.
Check: Every factor of ten in [H+] shifts the pH by exactly one unit.
Watch for this: A pH ABOVE 7 means fewer H+ ions, not more - the scale runs backwards to intuition.
Now try it yourself
A solution at pH 9. [H+] and character?
Check your answer
[H+] = 10^-9 mol/L, basic.
pH 9 is two units above neutral, so H+ is scarce and the solution is basic.
Neutralisation stoichiometry
Choose the method: Acid + base -> salt + water; HCl and NaOH pair 1:1.
EZT practice question
How many moles of NaOH exactly neutralise 1 mole of HCl, and what forms?
Show the worked solution
- HCl + NaOH -> NaCl + H2O.
- One H+ pairs with one OH-.
Answer: 1 mole of NaOH, giving sodium chloride and water.
Check: The resulting solution of a strong-acid-strong-base salt is neutral, pH 7.
Watch for this: Neutralisation does not always give pH 7 - a salt of a weak parent tips acidic or basic.
Now try it yourself
Moles of NaOH for 0.5 mole of HCl?
Check your answer
0.5 mole.
The pairing stays 1:1 whatever the amount.
The limewater test
Choose the method: CO2 turns limewater milky by forming CaCO3.
EZT practice question
Write the word equation when carbon dioxide is passed through limewater, and state the observation.
Show the worked solution
- Limewater is calcium hydroxide solution.
- CO2 + Ca(OH)2 -> CaCO3 + H2O.
Answer: Carbon dioxide + calcium hydroxide -> calcium carbonate + water; the solution turns milky as white CaCO3 precipitates.
Check: This is the standard test for CO2 - the same gas that acids release from carbonates in 2.1.3.
Watch for this: Excess CO2 redissolves the milkiness as soluble calcium hydrogencarbonate - the test works on moderate gas flow.
Now try it yourself
Which gas do acids release from metal carbonates?
Check your answer
Carbon dioxide.
Section 2.1.3: carbonate plus acid gives salt, water and CO2.
Metal meets acid
Choose the method: Active metal + acid -> salt + hydrogen gas.
EZT practice question
Zinc granules are dropped into dilute sulphuric acid. Write the word equation and name the gas.
Show the worked solution
- Zinc is more reactive than hydrogen.
- Zn + H2SO4 -> ZnSO4 + H2.
Answer: Zinc + sulphuric acid -> zinc sulphate + hydrogen; bubbles of hydrogen gas rise, and a burning splint pops at the mouth of the tube.
Check: The pop test is the classic confirmation of H2 from section 2.1.2.
Watch for this: Not every metal reacts - copper sits below hydrogen and stays quiet in dilute acid.
Now try it yourself
Magnesium + hydrochloric acid. Products?
Check your answer
Magnesium chloride + hydrogen.
Mg + 2HCl -> MgCl2 + H2, the same active-metal pattern.
Water of crystallisation
Choose the method: Many salt crystals lock water molecules into their structure.
EZT practice question
Name the salt CuSO4.5H2O and explain what the 5H2O means.
Show the worked solution
- CuSO4 is copper sulphate.
- The dot marks water of crystallisation - five water molecules per formula unit.
Answer: Hydrated copper sulphate (blue vitriol); each formula unit carries five water molecules, which give the crystal its blue colour and leave as a white powder on heating.
Check: Washing soda is Na2CO3.10H2O and gypsum is CaSO4.2H2O - heat gypsum and it loses water to become plaster of Paris.
Watch for this: The water is chemically bound, not wetness - dry-looking crystals can hold plenty of it.
Now try it yourself
Gypsum CaSO4.2H2O loses water on gentle heating. What forms?
Check your answer
Plaster of Paris, CaSO4.1/2 H2O.
It keeps only half a water molecule per formula unit and sets hard when mixed back with water.
Try a mixed set
Choose a method or explanation before opening each answer.
1. pH formula?
Show answer and reason
pH = -log[H+].
One unit per factor of ten.
2. Neutralisation?
Show answer and reason
Acid + base -> salt + water.
H+ pairs with OH-.
3. Limewater test?
Show answer and reason
CO2 turns limewater milky.
CaCO3 precipitates.
4. Safe dilution?
Show answer and reason
Add acid to water, stirring.
The heat of dilution can spurt concentrated acid.
Try it yourself
Work these on paper before checking any notes. Answers are deliberately not shown here.
- Find the pH of 0.001 M HCl.
- A solution is at pH 9. Is it acidic or basic, and what is [H+]?
- Name the product when gypsum is gently heated.
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Questions about this practice page
- Why does dry HCl gas not change dry litmus paper?
- Acidic behaviour needs H+ ions, and HCl only splits into ions in water. With no water there are no free H+ ions, so the gas is not acidic and the dry litmus stays put.
- What does pH actually measure?
- The hydrogen-ion concentration of a solution, compressed into a 0 to 14 scale: pH 7 is neutral, lower is acidic, higher is basic, and each step is a factor of ten in H+ concentration.
- Why do you always add acid to water, never water to acid?
- Mixing releases a lot of heat. Acid poured slowly into water spreads the heat through the bulk; a splash of water onto concentrated acid boils instantly at the surface and can spurt acid onto you.
- Are all salt solutions neutral?
- No. A salt's pH follows its parents: strong acid plus strong base gives neutral (like NaCl), strong acid plus weak base gives acidic, and weak acid plus strong base gives basic (like sodium carbonate).
- Are these the NCERT exercise questions for Acids, Bases and Salts (Class 10)?
- No. EZT pages are original practice following the chapter's section order - use them to prepare for the textbook exercises, not as a substitute for your book.