The hardness of water can be determined by volumetrically using the reagent (a) sodium thio sulphate (b) potas

Choose the Best Answer · Q9

Q. The hardness of water can be determined by volumetrically using the reagent

(a) sodium thio sulphate

(b) potassium permanganate

(d) EDTA

Tamil Nadu DgeTextbookSubjectiveImportance★★★★★

27% · 17/64 Questions

🔒 Locked · start free trial →

You're viewing a preview — the full solution, concept, methods & PYQ mapping are locked.

Start your 14-day free trial to unlock the full solution →

Step 1. EDTA (ethylenediaminetetraacetic acid) forms strong, selective 1:1 complexes with Ca²⁺ and Mg²⁺ ions.

Step 2. Titrating a water sample against a standard EDTA solution (with a suitable metal-ion indicator such as Eriochrome Black T) therefore gives a direct, quantitative volumetric measure of total hardness. …

Start your 14-day free trial to unlock the full solution →

Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

CBSE 2025Set ANNUAL1 markMCQ
$Q. Assertion : Permanent hardness of water is removed by treatment with Washing soda. Reason : Washing soda reacts with soluble Calcium and Magnesium chlorides and sulphates in hard water to form insoluble carbonates.$
(a) Assertion is true but Reason is false.
(b) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(c) Both Assertion and Reason are false.
(d) Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
›Reveal solutionSolution

Both statements are individually true, and the reason correctly explains the assertion: washing soda removes permanent hardness precisely because it converts soluble Ca2+/Mg2+ salts into insoluble carbonates that precipitate out.

Permanent hardness of water is caused by dissolved chlorides and sulphates of calcium and magnesium (unlike temporary hardness, which is caused by their bicarbonates and can be removed simply by boiling).

Washing soda, Na2CO3, removes this permanent hardness by a double-displacement (precipitation) reaction:

CaCl2(aq) + Na2CO3(aq) -> CaCO3(s) (down arrow) + 2NaCl(aq)

MgSO4(aq) + Na2CO3(aq) -> MgCO3(s) (down arrow) + Na2SO4(aq)

The soluble calcium/magnesium chloride and sulphate salts are converted into insoluble calcium/magnesium carbonate, which precipitates out and is removed (e.g. by filtration/settling), leaving the water softened.

…

Start your 14-day free trial to see the full solution →
CBSE 2023Set ANNUAL1 mark
$Q. Fill in the blank: The chemical formula of permutit is __________.$
›Reveal solutionSolution

Permutit is hydrated sodium aluminium silicate, Na2Al2Si2O8·xH2O, used as an ion-exchange resin to soften hard water.

Hard water contains dissolved Ca2+ and Mg2+ salts. Permutit is a synthetic zeolite (a sodium aluminosilicate) that removes this hardness by ion exchange: when hard water is passed through a bed of permutit, the Na+ ions in the permutit are exchanged for the Ca2+/Mg2+ ions in the water, which get trapped in the permutit lattice while soft (Na+-ri …

Start your 14-day free trial to see the full solution →

←Previous questionQ8 — If a body of a fish contains 1.2 g hydrogen in its total body mass, if…→Next questionQ10 — The cause of permanent hardness of water is due to (a) Ca(HCO₃)₂ (b) M…

Q.The hardness of water can be determined by volumetrically using the reagent

Concept understanding — Hard and Soft Water — Causes and Softening

Q.The hardness of water can be determined by volumetrically using the reagent

🎓Unlock everything free for 14 days

Unlock everything free for 14 days