chemistry Unit 18 learning aim A

unit 18: Industrial Chemical Reactions

Learning aim A: investigate chemical thermodynamics in order to understand spontaneous reactions

Assignment Title: Enthalpy and Entropy

Experiment 1: Enthalpy of Nutralisation

Hydrochloric acid and sodium hydroxide solution are used in this experiment. The concentration of both
solutions is 0.5 mol dm-3. You must calculate the enthalpy of neutralisation after determining the
temperature rise for the neutralisation of a sample of hydrochloric acid by sodium hydroxide.

Equipment

 Hydrochloric acid solution
 Sodium hydroxide solution
 Polystyrene cup
 Thermometer
 Distilled/deionised water
 Burette
 Pipette
 Pipette filler
 Small funnel
 Lab coat
 Safety glasses

Health and safety

Hydrochloric acid solution: irritant, it is corrosive to the skin and eyes. Inhalation exposure might cause
nose, eye and respiratory tract irritation and inflammation. To prevent this, wear goggles and a lab coat.
While handing it out be careful.

Sodium hydroxide solution: irritant, if eaten or drunken sodium hydroxide it can cause severe burns and
immediate vomiting, diarrhea, nausea, and chest and stomach pain. To avoid this, wear goggles and a
lab coat. May be gloves and mask to stop it from contacting you.

Method

1. Rinse the burette with hydrochloric acid. Set up the burette and fill it with hydrochloric acid
using a funnel
2. Transfer 25.0 cm3 of the hydrochloric acid in the burette into a dry and clean beaker
3. Measure the temperature of hydrochloric acid, write it down in one decimal place
4. Use distilled/de-ionised water to rinse the thermometer and then dry
5. With the sodium hydroxide solution rinse a pipette. Then using this pipette, transfer 25.0 cm3 of
the sodium hydroxide solution into a polystyrene cup.
6. Put the polystyrene cup in a beaker. Use a clamp stand to mount the thermometer in the cup.
Make sure the bulb does not touch the sides and bottom of the cup, and place a stirring rod in
the cup

, 7. Using a stirring rod stir the sodium hydroxide solution and measure the temperature to one
decimal place. Continue to measure the temperature for up to 3 minutes and record each result
in the drawn table
8. At the 4th minute pour the 25.0 cm3 of hydrochloric acid. Stir but do not record the
temperature.
9. Keep stirring the mixture and measure the temperature for up to 10 minutes and remember to
record the results to 1 decimal place in the table.

Table

Time (in minutes) Temperature
1 25
2 25
3 25
4
5 28
6 28
7 28
8 27
9 27
10 27


Graph

, Calculation

Heat energy change and enthalpy change

q=m x c x ∆t =

∆T = T2 – T1



50 x 4.18 x 3 = 627 j

Moles of sodium hydroxide (NaOH) = 0.5 mols

Moles of hydrochloric acid (HCI) = 0.5 mols

Moles = 0.5 x 25/1000 = 0.0125 mols

∆H = q/mol = 627/0.0125 = 50160 j/mol

50160/1000 = 50.16 kJ/mol



Experiment 2: To find the enthalpy change

Workout the enthalpy changes in KJ per mol from the temperature changes measured for dissolving
ammonium chloride in water.

Equipment

 Polystyrene cup
 Glass rod
 Thermometer
 Measuring cylinder
 Ammonium chloride
 Distilled water
 Stopwatch
 Weight scale

Health and safety

Ammonium chloride solid: harmful if swallowed. It can cause serious eye irritation. To prevent this,
wear eye protection and lab coats while handing.

Method

1. Measure 100 cm3 of water using measuring cylinder and pour into a polystyrene cup
2. Use a thermometer and record the temperature of the water
3. Use a weight scale to measure 5 grams of ammonium chloride. Add the ammonium chloride into
the water and stir using a stirring rod. Keep recording the temperature every 10 minutes until all
ammonium chloride is dissolved
4. Write down your results on a table