Question

B. There are usually about 20 drops of aqueous solution in 1ml. If a drop of sodium hydroxide should cling to the buret tip, how would it affect your resulting value of molarity?

C. Sodium hydroxide is a commonly used base in neutralization titrations. It is a normal procedure to determine the molarity by standardizing with an acid such as KHP. Why don’t we just weigh the sodium hydroxide and then calculate the molarity?

D. Prior to dissolving KHP, you are instructed to boil the distilled water. By boiling

the water, you are removing CO₂, and thus carbonic acid, from the solution. If you were to use non-boiled water, would you use up more NaOH solution in the titration, or would you use less? Explain how you came to your answer

E. Titrating using indicators have limitations. Describe one limitation using a change of solution color to indicate the endpoint of a titration.

Answer 1

B:)

If a drop of Sodium hydroxide remains on the buret tip, it means that we have 1 drop less of NaOH or 1/20 ml less of NaOH present in the solution whose molarity we are measuring. Due to this, moles of NaOH that we would measure would be lesser than what it would have been had the drop of NaOH not remained on buret tip whereas the volume of solution is the same. Thus, the molarity that we measure would turn out to be lesser than the actual/correct value.

C:)

NaOH is highly hygroscopic in nature which means that it readily abosrbs water molecules from air making it extremely tough to get an accurate measure of it's weight when weighing it directly as this would also include the weight of water that it abosrbed and thereby report a number which would be higher than the actual amount of NaOH present. Therefore, we titrate it against an acid of known molarity to determine it's concentration. This procedure is called standardization.

D:)

If we use non-boiled water, there would be some Carbonic acid already present in the solution. Some amount of NaOH would be used to neutralize this too. Since the KHP amount being used in both cases is same, we would end up using more NaOH solution during titration against KHP in the case of using non-boiled water because we use up some extra NaOH solution to neutralize the Carbonic acid already present in solution.

E:)

Since the colour change is a fairly subjective thing, meaning it can vary from person to person, it is very likely that one person reports the change of colour at the end point 2-3 drops before or after another person. This gives way to inaccuracy in measurement which is mostly reduced by taking multiple titration measurements and then averaging out the results.