Required practicals

Question 1

Describe how to prepare a standard solution

Answer 1

1. Weigh the sample bottle containing the solid on a (2 dp) balance.
2. Transfer solid to beaker and reweigh sample bottle.
3. Record the difference in mass.
4. Add distilled water and stir with a glass rod until all the solid has dissolved.
5. Transfer to a volumetric flask with washings.
6. Make up to the 250cm3
   mark with distilled water.
7. Shake flask.

Question 2

Describe a method for determining the concentration of an unknown solution of hydrochloric acid, using a 0.1mol dm-3 solution of sodium hydroxide by an acid-base titration

Answer 2

• rinse burette with sodium hydroxide to remove impurities
• overfill burette with sodium hydroxide and run through so jet space is filled
• use a volumetric pipette to transfer 25cm3 hydrochloric acid to conical flask
• add 2 drops of phenolphthalein
• slowly add NaOH to the acid and swirl
• stop at colour change from colourless to pink
• repeat until concordant results and calculate a mean

Question 3

Describe how you would measure the enthalpy change when copper sulfate dissolves in water

Answer 3

• measure 50cm3 of water using a volumetric pipette
• transfer to polystyrene cup with lid
• measure 4g of copper sulfate using an accurate balance
• use a precise thermometer to measure the temperature of the water each minute for 4 minutes
• pour copper sulfate into water at minute 5
• reweigh weighing boat
• replace lid and stir
• record the temperature at minute intervals for 15 minutes
• plot temperature against time graph