Partnership Division, University of Greenwich at Medway, Pembroke Building, Chatham Maritime ME4 4TB

The University of Greenwich is running a practical session for Chemistry students in Year 13

Assessed Chemistry Practical Lab Session for A2

Thermometric Titration of a Strong Acid Wednesday 28 March at 12.30 – 3.00 pm University of Greenwich, Medway Campus

This free session is open to all students on a first come first served

basis. Please see accompanying information for further information.

Programme:

12.30 Arrival and briefing

1.00 Chemistry Practical session begins

2.30 Post-activity Assessment

3.00 End

For bookings and enquiries, contact C.S.Bushnell@greenwich.ac.uk

Partnership Division, University of Greenwich at Medway, Pembroke Building, Chatham Maritime ME4 4TB

Thermometric Titration of a Strong Acid

(Time required for this experiment: 1.30 hr with an addition of 30 min for post assessment)

Start: 1.00 PM on Wednesday the 28th of March till 3.00 PM

Location: Link Lab (School of Science, University of Greenwich, Medway)

Aims:

The aims of the practical session are to use thermometric titration to determine the

concentration of a strong acid HA. Neutralisation is an exothermic reaction and the maximum

temperature is reached at the end-point. From your results, you will draw a graph of

temperature against the volume of strong acid HA added.

Assessment on:

Your ability to work carefully and safely, making accurate measurements and detailed

observations and record all your results clearly in an appropriate way.

Carrying out the titration (reading and recording burette volumes and temperature

values accurately).

Drawing and interpreting the graph to find the volume added of the strong acid.

You will be supplied with the followings:

• 1.0 M sodium hydroxide solution

• Concentrated hydrochloric acid (HA)

The neutralisation point in this titration occurs when the optimum volume of sodium

hydroxide solution (needed to exactly neutralise the amount of strong acid used) has been

added to the acid. Neutralisation is an exothermic reaction and the maximum temperature is

reached at the end-point

Partnership Division, University of Greenwich at Medway, Pembroke Building, Chatham Maritime ME4 4TB

At the end point of the titration of a strong avid and base the temperature is maximum. An

addition of a little amount of the acid in solution will take the temperature down.

Methods:

Transfer 50cm3

of sodium hydroxide solution to a polystyrene cup. Allow it to stand

for a few minutes, and then record the temperature of the solution.

Add 5.0cm3 of hydrochloric acid from a burette to the cup.

Immediately stir the mixture with the thermometer and record its temperature.

Repeat the above step until you have added a total of 50.0cm3

of acid (total 10 steps

additions of 5.0cm3 HCl).

Analysis:

Plot a graph of temperature (vertical axis) against total volume of acid added

(horizontal axis).

Draw straight lines of best fit and extend them until they cross (see diagram above).

The point at which the two lines meet corresponds to the volume of acid needed for

neutralisation and to the maximum temperature.

Record the volume needed for HCl

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

Evaluations and post assessments:

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.

Use the equation below to calculate the acid concentration

Partnership Division, University of Greenwich at Medway, Pembroke Building, Chatham Maritime ME4 4TB

Cb x Vb = Ca x Va

Where,

Cb = concentration of base (NaOH)

Vb = Volume of the base (NaOH)

Ca = Concetration of HCl

Va = Volume used of HCl

Now calculate the volume of HCl needed to neutralise 25cm3 of NaOH 1.0M solutions.

At this volume the solution shows the highest temperature during the titration. The

concentration for the HCl used is 2.0M.

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, Goggles, Labcoats and eye protection.

If spilt, wash with a lot of water.