Question

Question 5.6 The drain cleaner, Drainex contains small bits of aluminum which react with caustic soda to produce dihydrogen. What volume of dihydrogen at 20 °C and one bar will be released when 0.15g of aluminum reacts?

Class XI States of Matter Page 153

Answer 1

Al react with caustic soda to produce dihydrogen. reaction will be
2Al + 2NaOH + 2H2O -->2NaAlO2 + 3H2

here we see that, 2 mol of Al produce 3 mole of H2
∴ 2 × 27 g of Al produce 3 × 2 g of H2 .
∴ 54 g of Al produce 6g of H2.
∴ 1 g of Al produce 6/54 = 1/9 g of H2.
∴ 0.15g of Al produce 0.15/9 g of H2

so, number of mole of H2 produce = weight of HE produce/molar weight of H2
= (0.15/9)/2
= 0.15/18 = 0.00833 mol

now, use formula, PV = nRT
Here, P = 1 bar or 0.987 atm
T = 20°C or 293K
n = 0.00833 mol
R = 0.0821 atm dm³/K/mol
V = ?

V = 0.00833 × 0.0821 × 293/0.987
= 0.203 dm³
we know, 1 dm³ = 1000 mL
so, Volume of H2 = 1000× 0.203mL = 203mL

Answer 2

Answer : 201 mL of dihydrogen will be released.

Explanation : Aluminium reacts with caustic soda in accordance with the reaction

The reaction of aluminium with caustic soda can be represented as:

Therefore volume of hydrogen at STP released when 0.15g of Al reactsv

=0.15 x 3 x 22.4 /54 = 187ml

Now P1 = 1 bar,

P2 = 1 bar

T1 = 273 K

T2 = 20 + 273 = 293 K

V1 = 187 ml

V2 = x

When pressure is held constant,then

V2 = P1 V1 T2 / P2 T1

OR

x = 1 X 187 X 293 / 0.987 X 273

= 201 ml

Therefore, 201 mL of dihydrogen will be released.

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