MHT CET · Chemistry · Solutions

$5.0 g$ of sodium hydroxide $(M o l a r m a s s 40 g m o l^{- 1})$ is dissolved in little quantity of water and the solution is diluted up to $100 m l$ . What is the molarity of the resulting solution?

A $0.1 m o l d m^{- 3}$
B $1.0 m o l d m^{- 3}$
C $0.125 m o l d m^{- 3}$
D $1.25 m o l d m^{- 3}$

Verified Solution

Answer & Solution

Correct Answer

(D) $1.25 m o l d m^{- 3}$

Step-by-step Solution

Detailed explanation

Molarity

= \frac{N o . o f m o l e s}{p e r l i t r e S o l u t i o n}

No. of moles

= \frac{M a s s}{M o l a r m a s s}

= \frac{5}{40 g m o l^{- 1}} = 0.125 m o l

The solution is diluted up to 100 ml.
Hence, 100 ml consists of 0.125 mol of NaOH.
1 L consists of 'x' mole of NaOH

∴ x = \frac{0.125 \times 1000 m l}{100 m l} = 1.25 m o l d m^{- 3}

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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5.0 g of sodium hydroxide Molar mass 40 g mol-1 is dissolved in little quantity of water and the solution is diluted up to 100 ml . What is the molarity of the resulting solution?

Step-by-step Solution

$5.0 g$ of sodium hydroxide $(M o l a r m a s s 40 g m o l^{- 1})$ is dissolved in little quantity of water and the solution is diluted up to $100 m l$ . What is the molarity of the resulting solution?