Question

1. If the bubble in the tip of the buret is not removed prior to performing the HCl titration, will the reported concentration of the HCl be greater than, less than, or equal to the true concentration of the HCl if the bubble is pushed from the buret during the titration? Explain your answer. 2. Explain why it is not always necessary to refill the buret after every titration. 3. Explain why it is not necessary to dry the Erlenmeyer flask after rinsing it out between successive trials. 4. Suppose that the lab prep staff incorrectly recorded the masses of KHP. You are told they used 0.50 g of KHP to standardize the NaOH solution; however, they actually used 0.10 g KHP in the standardization. What will this do to your calculated concentration of the unknown HCL solution? Explain your answer

Answer 1

1. If the bubble is not removed during titration, the recorded volume of the NaOH solution added will be higher than the actual volume added. This is because, the bubble will also add to the burette reading and introduce an error. As the recorded volume of the NaOH solution added will be higher, this will give the impression that the concentration of HCl is higher than the actual value. You will be considering that more volume of NaOH is required to neutralize the volume of acid, therefore the acid solution has more acid present thus higher concentration.

2. The amount of NaOH solution to be added from burette will depend on the concentration of the acid solution and the quantity of acid solution taken. If the concentration of the acid solution is low or the volume of the acid solution taken in the flask is low, then you will require lesser volume of NaOH solution to titrate. Even if the burette is not completely filled, it may still have sufficient NaOH solution to complete the titration. Only thing you have to make sure is that the exact readings of the burette are recorded before and after the titration. The difference of these values is what is important, not the initial reading of the burette.

3. Water has 7 PH. It is neutral and will not take part in the titration. Presence of traces of water in the flask will not impact the end point of the titration. Therefore it is not necessary to dry the flask in between successive titrations.

4. Let us look at this scenario

Actual KHP is 0.1 g and this requires X ml of NaOH solution

Now you think that you have taken 0.5g KHP. The experimental volume of NaOH solution is still X ml. So you will assume that more NaOH is present in X ml of rhe solution.

Now molarity is moles /L

The volume remains same in both cases. But for the second case, more NaOH quantity (moles) will be assumed. Thus the calculated molarity of NaOH will be higher (roughly 5 times higher) than the actual molarity.

When you titrate HCl with this NaOH solution, you will be making all the calculations considering that the Molarity of NaOH solution is much higher than the actual volume. So as per the calculations, you will assume that higher moles of NaOH are required for the titration.

This will lead to the error where you will calculate the concentration of your HCl to be much higher than the actual concentration.