Question

A) How would your final result for the % KHP in the unknown be affected (if at all) if the water used to prepare your unknown solution and your standard KHP solution was CO2-free, but the water used to prepare your NaOH solution was CO2-contaminated? Assume no other experimental error occurred.

B) How would your final result for the % KHP in the unknown be affected (if at all) if the water used to prepare your NaOH solution and your unknown solution was CO2-free, but the water used in your standard KHP solution was CO2-contaminated? Assume no other experimental error occurred

c) How would your final result for the % KHP in the unknown be affected (if at all) if the water used to prepare your NaOH solution and your standard KHP solution was CO2-free, but the water used in your unknown solution was CO2-contaminated? Assume no other experimental error occurred.

Answer 1

A) NaOH reacts with water to form Na2CO3

2NaOH + CO2 --> Na2CO3 + H2O

this reduced the overall OH- present for titration in NaOH solution prepared.

If the water used for the preparation of NaOH has CO2 contamination, the resultant NaOH concentration would be lower than expected value. Less amount of OH- available for titration with KHP. Therefore, overall more volume of KOH would be required to neutralize KHP is titration than the theoretical value calculated. The end reult for the %KHP would be higher than actual amount of KHP present.

B) If the water used for the preparation of KHP is contaminated with CO2. No effect would be seen on the concentration of KHP. However, KHP + CO2 (contamination) would both react with added NaOH during titration. More amount of NaOH would be needed to reach the end point and would result in error in experiment. Again the % KHP calculated by titration would be higher than the true value.

C) If the water used for preparation of unknown has CO2 contamination. It would need more amount of OH- for titration, greater than the theoretical value. this would thus give a higher value for result and leads to error in titration. The %KHP result would be greater than the actual value.