JEE Main · 2020 · 07 Jan 2020 · Shift 2 · Surface Chemistry

The flocculation value of HCl for arsenic sulphide sol is

30 m mol L^{- 1}

. If

H_{2} SO_{4}

is used for the flocculation of arsenic sulphide, the amount, in grams of

H_{2} SO_{4}

in 250 mL required for the above purpose is ____ (Molecular mass of

H_{2} SO_{4} = 98 g / mol

)

Answer: 0.3675

Solution

Arsenic sulphide sol is negatively charged, so the flocculating power comes from the cation. A flocculation value of

30

mmol/L of HCl means

250

mL needs

\frac{30}{4} = 7.5

mmol of

H X^{+}

. Because each

H X_{2} SO X_{4}

supplies two

H X^{+}

ions, only half as many moles are needed,

\frac{7.5}{2} = 3.75

mmol, and the mass is

3.75 \times 1 0^{- 3} \times 98 = 0.3675

JEE Main · 2020 · 07 Jan 2020 · Shift 2 · Numerical answer