a solution containing 4.2g KOHand Ca(OH) 2 is neutralized by an acid. it consumes 0.1 equivalent of acid, calculate the percentage composition of the sample
To calculate the percentage composition of the sample, we need to determine the amounts (in grams) of the components present in the solution.
Given:
- The solution contains 4.2g KOH and Ca(OH)2.
- The acid consumed 0.1 equivalent.
Step 1: Determine the molar mass of each compound.
- Molar mass of KOH = atomic mass of K + atomic mass of O + atomic mass of H
= 39.10 g/mol + 16.00 g/mol + 1.01 g/mol
= 56.11 g/mol
- Molar mass of Ca(OH)2 = atomic mass of Ca + (atomic mass of O × 2) + (atomic mass of H × 2)
= 40.08 g/mol + (16.00 g/mol × 2) + (1.01 g/mol × 2)
= 74.10 g/mol
Step 2: Calculate the moles of each compound.
- Moles of KOH = mass of KOH / molar mass of KOH
= 4.2 g / 56.11 g/mol
= 0.075 mol
- Moles of Ca(OH)2 = mass of Ca(OH)2 / molar mass of Ca(OH)2
= 4.2 g / 74.10 g/mol
= 0.057 mol
Step 3: Determine the mole ratio based on the acid consumption.
According to the given information, 0.1 equivalent of acid is consumed. Since equivalent weight is defined as the molar mass divided by the number of acidic or basic equivalents, we need to determine the number of equivalents for each compound.
- Equivalents of KOH = moles of KOH / (number of acidic or basic equivalents per mole of KOH)
= 0.075 mol / 1 [KOH has 1 basic equivalent]
= 0.075 equivalents
- Equivalents of Ca(OH)2 = moles of Ca(OH)2 / (number of acidic or basic equivalents per mole of Ca(OH)2)
= 0.057 mol / 2 [Ca(OH)2 has 2 basic equivalents]
= 0.0285 equivalents
Step 4: Calculate the amount of each compound that reacts.
Since the acid consumed is limiting, we will focus on the amount consumed by the acid.
- Amount of KOH consumed = equivalents of KOH × molar mass of KOH
= 0.1 equivalents × 56.11 g/mol
= 5.611 g
- Amount of Ca(OH)2 consumed = equivalents of Ca(OH)2 × molar mass of Ca(OH)2
= 0.1 equivalents × 74.10 g/mol
= 7.41 g
Step 5: Calculate the percentage composition of the sample.
- Percentage of KOH = (amount of KOH consumed / total sample mass) × 100%
= (5.611 g / 4.2 g) × 100%
≈ 133.6%
(Note: The percentage of KOH is greater than 100% because the amount consumed exceeds the initial mass. This indicates that the KOH is in excess in the solution.)
- Percentage of Ca(OH)2 = (amount of Ca(OH)2 consumed / total sample mass) × 100%
= (7.41 g / 4.2 g) × 100%
≈ 176.4%
(Note: The percentage of Ca(OH)2 is greater than 100% for the same reason as mentioned above.)
Therefore, the percentage composition of the sample is approximately 133.6% KOH and 176.4% Ca(OH)2.
KOH = 35%,
Ca(OH) 2 = 65%
Hoped it helped!