50gm of a sample of ca(oh)s is dissolved in 50ml of 0.5N hcl solution. The excess of hcl was titrated with 0.3N -naoh. The volume of naoh used was 20cc. Calculate of naoh used was 20cc. Calculate % purity ca(oh)2
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To calculate the percentage purity of Ca(OH)2, we need to determine the number of moles of Ca(OH)2 present in the sample and compare it to the number of moles of Ca(OH)2 that should be present if the sample was pure.
Here are the step-by-step calculations:
Step 1: Calculate the number of moles of HCl used to react with the Ca(OH)2.
Since we know the concentration of HCl (0.5 N) and the volume used (50 mL), we can calculate the number of moles of HCl as follows:
Number of moles of HCl = concentration × volume
= 0.5 N × 0.050 L
= 0.025 moles
Step 2: Calculate the number of moles of NaOH used.
Since we know the concentration of NaOH (0.3 N) and the volume used (20 mL), we can calculate the number of moles of NaOH as follows:
Number of moles of NaOH = concentration × volume
= 0.3 N × (20/1000) L
= 0.006 moles
Step 3: Calculate the excess moles of HCl.
The total moles of HCl used is equal to the moles of NaOH used because the reaction is stoichiometrically balanced. Therefore, the excess moles of HCl can be calculated by subtracting the moles of NaOH used from the total moles of HCl used:
Excess moles of HCl = Total moles of HCl used - Moles of NaOH used
= 0.025 moles - 0.006 moles
= 0.019 moles
Step 4: Calculate the number of moles of Ca(OH)2 reacted.
Since the balanced chemical equation between HCl and Ca(OH)2 is 2HCl + Ca(OH)2 -> CaCl2 + 2H2O, we know that 2 moles of HCl react with 1 mole of Ca(OH)2. Therefore, the moles of Ca(OH)2 can be calculated as follows:
Moles of Ca(OH)2 = Excess moles of HCl / 2
= 0.019 moles / 2
= 0.0095 moles
Step 5: Calculate the mass of Ca(OH)2 in the sample.
The molar mass of Ca(OH)2 can be calculated by summing the atomic masses of calcium (Ca), oxygen (O), and hydrogen (H):
Molar mass of Ca(OH)2 = (Ca: 40.08 g/mol) + (O: 16.00 g/mol) + 2(H: 1.01 g/mol)
= 74.09 g/mol
Mass of Ca(OH)2 = Moles of Ca(OH)2 × Molar mass of Ca(OH)2
= 0.0095 moles × 74.09 g/mol
= 0.7047 grams
Step 6: Calculate the percentage purity of Ca(OH)2.
The percentage purity can be calculated by dividing the mass of pure Ca(OH)2 by the mass of the sample and multiplying by 100%:
Percentage purity = (Mass of pure Ca(OH)2 / Mass of the sample) × 100%
= (0.7047 g / 50 g) × 100%
= 1.41% purity
Therefore, the calculated percentage purity of Ca(OH)2 in the sample is approximately 1.41%.