A water sample has total hardness due to divalent ions of 3.00x10^-3 mol/L. Taking CaCO3 = 100 and Na2CO3 = 106 (all hardness precipitated as carbonates, 1 : 1), which of the following are correct?

The hardness is 300 ppm as CaCO3.

One litre of the sample contains hardness equivalent to 0.300 g of CaCO3.

25.0 mL of the sample needs 7.5 mL of 0.0100 M EDTA.

The hardness is 300 ppm as CaCO3.

One litre of the sample contains hardness equivalent to 0.300 g of CaCO3.

25.0 mL of the sample needs 7.5 mL of 0.0100 M EDTA.

Softening one litre needs 0.636 g of Na2CO3.

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JEE Main levelOne or more correct optionsDifficulty 2 of 3eq102

A water sample has total hardness due to divalent ions of $3.00 \times 1 0^{- 3}$ mol/L. Taking $CaCO X_{3}$ = 100 and $Na X_{2} CO X_{3}$ = 106 (all hardness precipitated as carbonates, 1 : 1), which of the following are correct?

AThe hardness is 300 ppm as $CaCO X_{3}$ .
BOne litre of the sample contains hardness equivalent to $0.300 g$ of $CaCO X_{3}$ .
C $25.0 mL$ of the sample needs $7.5 mL$ of $0.0100 M$ EDTA.
DSoftening one litre needs $0.636 g$ of $Na X_{2} CO X_{3}$ .

Answer: A, B, C

Hardness = 3.00e-3 x 100 = 0.300 g/L = 300 ppm. EDTA: 0.0250 x 3.00e-3 = 7.5e-5 mol / 0.0100 M = 7.5 mL. Na2CO3 needed is 1:1, i.e. 3.00e-3 x 106 = 0.318 g, not 0.636 g.

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A water sample has total hardness due to divalent ions of 3.00×10−3 mol/L. Taking CaCOX3​ = 100 and NaX2​COX3​ = 106 (all hardness precipitated as carbonates, 1 : 1), which of the following are correct?

Answer: A, B, C

More questions on Back titration and hardness of water

A water sample has total hardness due to divalent ions of $3.00 \times 1 0^{- 3}$ mol/L. Taking $CaCO X_{3}$ = 100 and $Na X_{2} CO X_{3}$ = 106 (all hardness precipitated as carbonates, 1 : 1), which of the following are correct?