To 200 g of sodium carbonate solution was added 200 g of a 19.6% sulfuric acid solution.

| May 22, 2021 | education

To 200 g of sodium carbonate solution was added 200 g of a 19.6% sulfuric acid solution. To completely neutralize the unreacted acid, 200 g of a 19.6% potassium hydroxide solution was added to the solution. Determine the mass fraction of salt in the original solution.

In order to solve this problem, we first write down the reaction equations:
Na2CO3 + H2SO4 = Na2SO4 + CO2 + H2O
H2SO4 + 2 KOH = K2SO4 + 2 H2O
Let’s start by calculating how much pure potassium hydroxide has reacted with the remains of sulfuric acid:
m (KOH) = [w (KOH) * m (solution)] / 100 = (200 * 19.6) / 100 = 39.2 (g)
Using the Periodic Table of D.I. Mendeleev, we calculate the molar masses of potassium hydroxide and sulfuric acid:
M (KOH) = 39 + 12 +1 = 52 g / mol
M (H2SO4) = 2 * 1 + 32 + 4 * 16 = 98 g / mol
now, by composing a proportion, we calculate the mass of the sulfuric acid residue, from the second reaction equation:
m (H2SO4) = [m (KOH) * M (H2SO4)] / 2 * M (KOH) = 39.2 * 98/2 * 56 = 3841.6 / 112 = 34.3 g.
For further calculations, we need to calculate the mass of pure sulfuric acid in the solution, which was added to sodium carbonate:
m (to-you) = [w (acid) * m (solution)] / 100 = (200 * 19.6) / 100 = 39.2 (g)
From here we calculate the mass of the acid that has reacted with sodium carbonate. To do this, from the total mass of acid in solution, subtract the mass of acid neutralized with potassium hydroxide:
m (acid) = m (all to-you) – m (to-you, reaction with KOH) = 39.2 – 34.3 = 4.9 g.
From the first reaction equation, we calculate, by composing the proportion of the mass of salt:
Using the Periodic Table of D.I. Mendeleev, we calculate the molar masses of potassium hydroxide and sulfuric acid:
M (Na2CO3) = 2 * 23 + 12 + 3 * 16 = 106 g / mol
M (H2SO4) = 2 * 1 + 32 + 4 * 16 = 98 g / mol
now, by composing a proportion, we calculate the mass of the sulfuric acid residue, from the second reaction equation:
m (Na2CO3) = [m (H2SO4) * M (Na2CO3)] / M (H2SO4) = 5.3 g.
And with the last action, we calculate the mass fraction of salt in the solution:
w (KOH) = m (Na2CO3) / m (solution) = 5.3 / 200 = 0.0265
or 2.65%.



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