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# 12.5 mL of a solution containing 6g of a dibasic acid in 1L was found to be neutralised by 10mL of a decinormal solution of NaOH. The molecular mass of the acid is:(a110(b)75(c)120(d)150

Last updated date: 13th Jun 2024
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Hint:Neutralisation is the process where a known quantity of acid and a base react to form salt and water. Using stoichiometric calculation we can solve the question.

It is given that the amount of acid in 1L solution = 6g
So, the amount of acid in 12.5mL solution will be = $\dfrac{6}{1000}\times 12.5g=0.075g$
When it is at neutralisation,
10mL of $\dfrac{N}{10}$NaOH = 10mL of $\dfrac{N}{10}$acid (it is given that decinormal which means$\dfrac{N}{10}$)
We calculated that $\dfrac{N}{10}$acid=0.075g
So, for 1000mL $\dfrac{N}{10}$acid=$\dfrac{0.075}{10}\times 1000=7.5$g
1000mL of N acid = 7.5x10 =75g
Therefore, we get the equivalent mass of the acid= 75
As the acid is dibasic, we need to multiply equivalent mass with 2 in order to calculate molecular mass.
Molecular mass= 75x2=150g
Thus, the correct answer to the question is option (d).

Only in neutralisation reaction we can take the condition 10mL of $\dfrac{N}{10}$NaOH = 10mL of $\dfrac{N}{10}$acid. We should also keep in mind to multiply the equivalent mass with 2, and then only we get the molecular mass.