Thermometric titration

Thermometric titration

Your task
You will use thermometric titration to determine the concentration of hydrochloric acid. Neutralisation is an exothermic reaction and the maximum temperature is reached at the end-point.

To gain full marks, you should:
• complete the experiment without guidance
(but remember – always ask for help if you need it);
• work carefully and safely, making accurate measurements and detailed observations; and
• record all your results clearly in an appropriate way.
Use the following reagents in your experiment:
• 1.000M sodium hydroxide solution
• approx. 2M hydrochloric acid
Method
1. Read through the Methods, then construct suitable blank tables for your Results.
2. Transfer 50cm3 of sodium hydroxide solution to a polystyrene cup.
Allow it to stand for a few minutes, then record the temperature of the solution.
3. Add 5.0cm3 of hydrochloric acid from a burette to the cup.
Immediately stir the mixture with the thermometer and record its temperature.
Repeat until you have added a total of 50.0cm3 of acid.
Analysis

1. Plot a graph of temperature (vertical axis) against total volume of acid added (horizontal axis). Total volume of acid added (cm3)Temperature (OC)
Draw straight lines of best fit and extend them until they cross (see diagram right).
The point at which the two lines meet corresponds to the volume of acid needed for neutralisation and to the maximum temperature.

2. Use information from your graph to calculate the concentration of the acid.

Evaluation
Comment on your results, their accuracy, and the likely sources of error in the experiment. Consider the limitations of the experiment, and possible improvements to it.

Thermometric titration
Technician’s Notes
Per pupil:
1 x polystyrene cup
1 x burette and stand
1 x 25cm3 pipette
1 x pipette filler
1 x plastic filter funnel
1 x thermometer

Per class:
sodium hydroxide solution: 1.000M (allow about 200cm3 per student)
hydrochloric acid: 2M approx. (allow about 150cm3 per student)
ethanoic acid: 2M approx. (allow about 150cm3 per student)

*Health and Safety Notes
Hydrochloric acid -Corrosive.
Refer to Hazcards for correct method to prepare the 2M (approx.) solution.
Ethanoic acid

Corrosive.

Harmful vapour.
Refer to Hazcards for correct method to prepare the 2M (approx.) solution.

Sodium hydroxide solid and solutions
Sodium hydroxide is very caustic and forms strongly alkaline solutions.
Exercise care in handling - wear gloves and eye protection.
If spilt, wash with a lot of water.