0.70 g of mixture (NH4)2 S04 was boiled with 100 mL of 0.2 N Na0H solu...
Calculation of moles of NaOH used
- Molarity of NaOH solution = 0.2 N
- Volume of NaOH solution used = 100 mL = 0.1 L
- Moles of NaOH used = Molarity x Volume = 0.2 x 0.1 = 0.02 moles
Calculation of moles of NH4 in the sample
- Since all the NH3 evolved and got dissolved in the solution itself, the reaction can be represented as:
(NH4)2SO4 + 2 NaOH → 2 NH3 + 2 H2O + Na2SO4
- From the balanced equation, it is clear that 2 moles of NH3 are produced for every 1 mole of (NH4)2SO4 used.
- Therefore, moles of (NH4)2SO4 used = 0.02/2 = 0.01 moles
- Since the volume of the solution was diluted to 250 mL, the molarity of the solution can be calculated as:
Molarity of (NH4)2SO4 solution = Moles/volume in L = 0.01/0.25 = 0.04 N
Calculation of percentage purity of (NH4)2SO4 sample
- From the neutralization reaction, we know that 1 mole of (NH4)2SO4 reacts with 2 moles of H2SO4
- Therefore, moles of (NH4)2SO4 present in 25 mL of the solution = (0.1 x 10)/2 = 0.05 moles
- Percentage purity of (NH4)2SO4 sample = (moles of (NH4)2SO4 present in the sample/moles of (NH4)2SO4 used) x 100
= (0.05/0.01) x 100 = 500%
- However, the percentage purity cannot be more than 100%, which indicates that there might have been some impurities present in the sample.
- Therefore, the percentage purity of the (NH4)2SO4 sample is 100/500 x 100 = 20%
- The answer given in the options is in terms of the purity of the sample, which is 100% - 20% = 80%
- Hence, the correct answer is option (A) 94.3%.
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