Module 1-Practical Skills

Question 1

Describe the experiment you would do to determine the formula of a hydrated salt.(5)

Answer 1

• weigh an empty crucible
• weigh crucible and salt
• support the crucible with a pipe-clay triangle
• heat gently for a minute and then strongly for a further 3 minutes
• reweigh the crucible and the remaining solid (until a constant mass has been reached).

Question 2

What assumptions are made during the calculation of the formula of a hydrated salt?(2)

Answer 2

• all water has been lost

- no further decomposition.

Question 3

Describe how you would calculate the relative molecular mass of a volatile liquid.(3)

Answer 3

• add a sample of the volatile liquid to a small syringe via a needle and weigh the syringe
• inject the sample into a gas syringe through the self-sealing rubber cap and then reweigh the small syringe to find the mass of the volatile liquid added to the gas syringe
• place the gas syringe in a boiling water bath at 100 degrees, the liquid vaporises producing a gas and the pressure is recorded.

Question 4

Describe how you could use a gas syringe, conical flask and HCl to identify an unknown metal.(3)

Answer 4

• Add a weighed sample of the metal to flask and add 25cm3 HCl quickly
• measure the gas evolved and use this to calculate the moles
• you can then use stoichiometry from an equation to work it out.

Question 5

Describe how you would prepare a standard solution.(5)

Answer 5

• the solid is first weighed accurately using the weighing boat technique
• the solid is then dissolved in a beaker with distilled water using less than will be needed to fill the volumetric flask
• the solution is then transferred to a volumetric flask and the traces of solution are rinsed into the flask with distilled water
• the flask in then carefully filled to the graduation line with distilled water dropwise until the meniscus is level(view at eye level)
• then invert the flask several times to thoroughly mix the solution.

Question 6

Describe the titration procedure.(4)

Answer 6

• add a measured volume of one solution to the conical flask using a pipette and add indicator e.g. Methyl orange(red in acid yellow in alkali)
• add the other solution to the burette and record the initial burette reading to the nearest 0.05cm3
• run the solution into the conical flask (whilst swirling it) until a colour change occurs, known as the end point and is the approximate titre
• repeat the experiment, but this time when you get close to the approximate titre value begin to add the solution dropwise until the end point is reached(do this three times-or as many times it takes to achieve concordat results-to calculate the mean titre).

Question 7

Describe how you could use a titration to identify a carbonate.(2)

Answer 7

• make a solution making the carbonate and add 25cm3 to a conical flask
• titration with 0.1M HCl and use the results to identify the carbonate.