12.0g of a mixture of potassium carbonate and potassium chloride were
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12.0g of a mixture of potassium carbonate and potassium chloride were dissolved in a 250cm³ standard flask. 25cm³ of this solution required 40.00cm³ of 0.1 M HCI neutralization. What is the percentage by weight of K₂CO₃ in the mixture?
(K = 39, O = 16, C = 12)
A. 60
B. 72
C. 82
D. 92
QUICK ANSWER…
D
DETAILS…
Please note that:
Potassium carbonate is a base which will react and be neutralized by the acid HCl,
Potassium chloride is a salt which will remain inactive while the reaction occurs.
Equation of neutralization:
K₂CO₃ + 2HCl → 2KCl + H₂O + CO₂
We are going to be using acid – base equation to determine the molar concentration of the base.
What this simply mean is that the molar concentration of the base K₂CO₃ in the solution is 0.08 mol/cm³
But, mass concentration = molar concentration x molar mass
Molar mass of K₂CO₃ = 2(39) + 12 + 3(16) = 138g/mol
Therefore, mass concentration = 0.08 x 138 = 11.04g/cm³
But the mass of the mixture = 12 g/cm³
Hence, the percentage by mass/weight of K₂CO₃ in the mixture = (11.04/12) × 100 = 92%
Now for the right answer to the above question:
- Option A is incorrect.
- Option B is incorrect.
- C is incorrect.
- D is the correct answer.
KEY-POINTS…
You may please note these/this:
- Remember, the 250cm3 is not used in our calculation because it is merely the size of the flask, and we were not told it was filled to the brim.
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/ culled from 2015 JAMB-UTME Chemistry past question 8 /
