Core practical 1

Question 1

What is CP1?

Answer 1

It is finding the molar volume of a gas

Question 2

What is the method?

Answer 2

1) Place 30 cm3 of 1 mol dm−3 ethanoic acid in the boiling tube.
2) Set the apparatus up as shown in the diagram.
3) Place approximately 0.05 g of calcium carbonate in a test tube.
4) Weigh the test tube and its contents accurately.
5) Remove the bung from the boiling tube and tip the calcium carbonate into the boiling tube. Quickly replace the bung in the boiling tube.
6) Once the reaction is over, measure the volume of gas collected in the measuring cylinder.
7) Reweigh the test tube that had contained the calcium carbonate.
8) Repeat the experiment six more times, increasing the mass of calcium carbonate by about 0.05 g each time. Do not exceed 0.40 g of calcium carbonate.

Question 3

What are some key points?

Answer 3

Overall equation: CaCO3 + 2CH3COOH → Ca(CH3COO)2 + CO2 + H2O
● Wait until no effervescence is observed before weighing flask containing acid and marble chips (CaCO3) to minimise gas loss.
● Don’t use too much CaCO3 so you don’t produce more gas than the measuring cylinder can fit.
● A weak acid is used so that the reaction is slower, meaning there is less gas loss between adding marble chips and attaching bung.
● An alternative method could involve attaching marble chips on a string to the bung, sealing the test tube with a bung, and then tipping the test tube so that the acid comes to the contact with the marble chip. This could reduce the loss of product.

Question 4

What are some errors that could occur?

Answer 4

● If using syringe, plunger may not be free moving. It may need a lubricant.
● CO2 is slightly soluble in water, so the exact volume is not measured as some may dissolve in solution.
● Some gas escapes between addition of marble chips and sealing the test tube.
● Bung may not be airtight.
● Transferring the solid. It is important to weigh the tube containing marble chips before the addition and reweigh after the addition. This method is ‘ weighing by difference’ and ensures the amount of CaCO3 that ends up in the reaction mixture is known

Question 5

What is avogadros law?

Answer 5

Equal volumes of gases at the same temp and pressure will contain an equal number of molecules

Question 6

What is the weighing by difference method?

Answer 6

Mass of substance = Mass of weighing dish and substance - mass of weighing dish after substance has been transferred

Question 7

What equipment would you need for this experiment?

Answer 7

Boiling tube

Stand and clamp

Bung fitted with delivery tube to fit boiling tube

100cm3 measuring cylinder

50cm3 measuring cylinder

test tube

mass balance (2 d.p.)

1 mol dm-3 ethanoic acid

powdered calcium carbonate

Question 8

How would you analyse the data?

Answer 8

Plot a graph of mass of CaCO3 on the x-axis against volume of CO2 collected on the y axis
Draw a line of best fit that passes through the origin
In this reaction, CACO3 to CO2 is a 1:1 ratio. You could calculate the number of moles of CaCO3 in 0.25g and use this to calculate the volume of 1 mol of CO2 in dm3

Question 9

What health and safety measures should you take?

Answer 9

Wear eye protection.

Remove the bung if the delivery tube gets blocked, clear blockage and repeat the procedure from the start.

Avoid skin contact with the ethanoic acid, especially if the skin is broken or sensitive.