Experiment 12: Titration of an unknown acid

Notes: The students have seen a titration demonstrated and should be familiar with the new apparatus: burette, pipette, filler.

Chemicals:

• Dilute hydrochloric acid - unknown concentration
• Sodium hydroxide 0,1M
• Phenolphthalein indicator

Instructions:

1. Fill the burette with the unknown dilute hydrochloric acid provided.
2. Using the pipette deliver 25cm3 of the sodium hydroxide solution into a clean conical flask and add three drops of phenolphthalein indicator.
3. Add the dilute hydrochloric acid to the solution in the conical flask until one drop just removes the colour. You will need to carry out the procedure in a rough way at first to find the approximate end-point before carrying out the procedure more accurately.

Write-up

Aim, Method and Diagram - no hypothesis needed

Data collection:

Record all of your readings and present them in suitable tables

Data analysis:

Given that the reaction between the acid and the base is in a 1:1 ratio in terms of the equation see if you can calculate the strength of the unknown acid solution. The calculation should go as follows:

No of moles of base = volume of base solution cm3/1000 x concentration of base solution

No of moles of acid = no of moles of base

concentration of acid = no of moles of acid/ volume of acid added.

Conclusions:

State what you have found out and give a summary of the new apparatus used.

Evaluation:

Where are the experimental weaknesses? Did you introduce any errors? How could you improve the experiment?