NVAEasyJEE 2026Stoichiometry & Calculations

JEE Chemistry 2026 Question with Solution

xx mg of pure HCl was used to make an aqueous solution. 25.0mL25.0 \, \text{mL} of 0.1M0.1 \, \text{M} Ba(OH)2_2 solution is used when the HCl solution was titrated against it. The numerical value of xx is _____ × 10110^{-1}. (Nearest integer) Given: Molar mass of HCl and Ba(OH)2_2 are 36.5g mol136.5 \, \text{g mol}^{-1} and 171.0g mol1171.0 \, \text{g mol}^{-1} respectively.

Answer

Correct answer:1825

Step-by-step solution

Standard Method

Given: pure HCl solution is titrated with 25.0mL25.0 \, \text{mL} of 0.1M0.1 \, \text{M} Ba(OH)2_2. Molar masses are 36.5g mol136.5 \, \text{g mol}^{-1} for HCl and 171.0g mol1171.0 \, \text{g mol}^{-1} for Ba(OH)2_2.

Find: the numerical value of xx in x×101x \times 10^{-1} mg.

At the end point of titration, equivalents of acid equal equivalents of base.

For Ba(OH)2_2, the nn-factor is 22.

Equivalents of Ba(OH)2=Molarity×Volume (L)×n-factor\text{Equivalents of } Ba(OH)_2 = \text{Molarity} \times \text{Volume (L)} \times n\text{-factor}=0.1×0.025×2=0.005 eq= 0.1 \times 0.025 \times 2 = 0.005 \text{ eq}

Therefore, equivalents of HCl are also 0.0050.005.

Since HCl has nn-factor 11, moles of HCl are 0.005mol0.005 \, \text{mol}.

Mass of HCl=Moles×Molar mass\text{Mass of HCl} = \text{Moles} \times \text{Molar mass}=0.005×36.5=0.1825 g= 0.005 \times 36.5 = 0.1825 \text{ g}

Converting to mg:

0.1825×1000=182.5 mg0.1825 \times 1000 = 182.5 \text{ mg}

Now,

182.5 mg=1825×101 mg182.5 \text{ mg} = 1825 \times 10^{-1} \text{ mg}

Hence, x=1825x = 1825.

Therefore, the value of xx is 1825.

Using Equivalents in Titration

Given: HCl is neutralized by Ba(OH)2_2.

Find: the integer value of xx.

The key idea is that Ba(OH)2_2 is a diacidic base, so each mole provides 2mol2 \, \text{mol} of OHOH^-.

Ba(OH)2Ba2++2OHBa(OH)_2 \rightarrow Ba^{2+} + 2OH^-

So the equivalent amount of base used is

0.1×0.025×2=0.0050.1 \times 0.025 \times 2 = 0.005

This equals the equivalent amount of HCl neutralized.

HClH++ClHCl \rightarrow H^+ + Cl^-

For HCl, one mole gives one equivalent, so

moles of HCl=0.005\text{moles of HCl} = 0.005

Mass of HCl:

0.005×36.5=0.1825 g0.005 \times 36.5 = 0.1825 \text{ g}

In milligrams:

0.1825 g=182.5 mg0.1825 \text{ g} = 182.5 \text{ mg}

Matching with the form x×101x \times 10^{-1} mg,

182.5=x×101182.5 = x \times 10^{-1}x=1825x = 1825

Therefore, the value of xx is 1825.

Common mistakes

  • Using the molarity of Ba(OH)2_2 directly as the acid equivalent amount is incorrect because Ba(OH)2_2 supplies 2OH2OH^- per mole. Multiply by 22 to get the correct equivalents.

  • Forgetting to convert 25.0mL25.0 \, \text{mL} into 0.025L0.025 \, \text{L} gives a mass larger by a factor of 10001000. Always convert volume to litres before using molarity.

  • Stopping at 0.1825g0.1825 \, \text{g} and not converting to mg leads to the wrong value of xx. Convert grams to milligrams before comparing with x×101x \times 10^{-1} mg.

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