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Some Basic Concepts of Chemistry question

2020 · 7 Jan · Shift 2 · Q17
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Some Basic Concepts of Chemistry question

2020 · 7 Jan · Shift 2 · Q17

JEE MainChemistrySome Basic Concepts of ChemistryNumerical+4 / −1
The flocculation value of HClHClHCl for arsenic sulphide sol. is 30 m mol L-1 If H2SO4H_2SO_4H2​SO4​ is used for the flocculatiopn of arsenic sulphide, the amount in grams, of H2SO4H_2SO_4H2​SO4​ in 250 ml required for the above purposed is ‾\underline{\hspace{2cm}}​. (molecular mass of H2SO4H_2SO_4H2​SO4​ = 98 g/mol)
Numerical answer
View written solutionFree

Correct answer: 0.36TO0.38

  1. Use Hardy–Schulze rule

For coagulation of a negatively charged sol like arsenic sulphide, the coagulating power depends on the valency of the oppositely charged ion.

If flocculation value for HCl\mathrm{HCl}HCl is given, the active ion is H+\mathrm{H^+}H+, which is monovalent.

For H2SO4\mathrm{H_2SO_4}H2​SO4​, the effective coagulating ion is again H+\mathrm{H^+}H+, and since each mole of H2SO4\mathrm{H_2SO_4}H2​SO4​ gives 2 moles of H+\mathrm{H^+}H+, the molar concentration of H2SO4\mathrm{H_2SO_4}H2​SO4​ needed will be half that of HCl\mathrm{HCl}HCl.

So,

C(H2SO4)=30 mmol L−12=15 mmol L−1C(\mathrm{H_2SO_4})=\frac{30\ \text{mmol L}^{-1}}{2}=15\ \text{mmol L}^{-1}C(H2​SO4​)=230 mmol L−1​=15 mmol L−1
  1. Find moles required in 250 mL250\,\text{mL}250mL

Volume:

250 mL=0.250 L250\,\text{mL}=0.250\,\text{L}250mL=0.250L

Moles of H2SO4\mathrm{H_2SO_4}H2​SO4​ required:

n=15×10−3×0.250n = 15\times 10^{-3}\times 0.250n=15×10−3×0.250 n=3.75×10−3 moln = 3.75\times 10^{-3}\ \text{mol}n=3.75×10−3 mol
  1. Convert moles to mass

Given molar mass of H2SO4=98 g mol−1\mathrm{H_2SO_4}=98\,\text{g mol}^{-1}H2​SO4​=98g mol−1

m=nM=3.75×10−3×98m = nM = 3.75\times 10^{-3}\times 98m=nM=3.75×10−3×98 m=0.3675 gm = 0.3675\,\text{g}m=0.3675g
  1. Final answer

Required mass of H2SO4\mathrm{H_2SO_4}H2​SO4​ in 250 mL250\,\text{mL}250mL is

0.368 g\boxed{0.368\ \text{g}}0.368 g​

As an integer-type entry rounded suitably, this is about 0.37 0.37\,0.37g.

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