Question

In an experiment, a solution sulfuric acid is mixed with an excess of sodium carbonate. One of the products is a gas. This gas is collected in a one-liter flask at 20.0°C. What will be the pressure in the flask if 113 mL of the sulfuric acid solution is used? The [H2SO4] can be found from its complete titration (25.0 mL H2SO4) with 16.0 mL of NaOH (NaOH : standardized with 58.7 mL of a 1.000 M HCl)

Answer 1

Molarity of NaOH solution required to neutralise 58.7ml of 1M HCl can be given by following equation,

16 x M_NaOH = 58.7 x 1

M_NaOH = 58.7 / 16

= 3.66875M

Now, this NaOH is being titrated with 25ml of H₂SO₄, So, for calculating Normality of H₂SO₄ we can write equation as,

25 x N_H2SO4 = 3.66875 x 16

N_H2SO4 = 3.66875 x 16 / 25

N_H2SO4 = 2.348N

Now, We know N_H2SO4 = 2 M_H2SO4

So, M_H2SO4 = 1.174M

So, no. of moles of H₂SO₄ in 113 ml = 1.174*113/1000

= 0.132662

Now, writing the Chemical reaction involved

H₂SO₄ + Na₂CO₃ Na₂SO₄ + H₂O + CO₂

So the gas evolved is CO₂. from balanced equation we can see that when 1 mol of sulphuric acid reacts, one mole of carbon dioxide evolves.

So, we can say that 0.132662 moles of carbon dioxide is evolving so, Pressure can be calculated using the following formula

PV = nRT

where, V = 1 L

n = 0.132662

R = 0.0821

T = 273+20 = 293K

So, P = (0.132662*0.0821*293) / 1

P = 3.19 atm.