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The hardness of water samle containing 0...

The hardness of water samle containing 0.002 mole of magnesium sulphate dissolved in a litre of water is expressed as

A

a) 20 ppm

B

b) 200 ppm

C

c) 2000 ppm

D

d) 120 ppm

Text Solution

Verified by Experts

The correct Answer is:
B
The hardness of water sample containing 0.002 mole of `MgSO_(4)` dissolved in 1 L of water.
Number of moles = `("mass")/("molecular mass")`
`0.02=("mass")/(120)`
mass `=240xx10^(-3)g`
i.e., `240xx10^(-3)g` mass of `MgSO_(4)` in 1 L of water.
`therefore 10^(3)g` of `H_(2)O` contains
= 0.240 g of `MgSO_(4)`
`therefore 10^(6)g` of `H_(2)O` contains
`=(0.240xx10^(6))/(10^(3))g" of "MgSO_(4)`
`=0.240xx10^(3)g" of "MgSO_(4)`
`therefore 10^(6)g` of water contains
`=240g" of "MgSO_(4)`
`120gMgSO_(4)-=100g" of "CaCO_(3)`
`240g" of "MgSO_(4)`
`=(100xx240)/(120)=200g" of "CaCO_(3)`
Hence, hardness of `H_(2)O=200` ppm
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