PAG 01a- Determination Of The Composition Of Copper (ii) Carbonate

Question 1

Describe how to set up the apparatus to measure the volume of gas produced in a reaction

Answer 1

A gas syringe or upside-down water-filled measuring cylinder in a trough of water may be used to collect the gas

Question 2

How can the number of moles of CO2 be calculated from the volume of CO2 collected during an experiment?

Answer 2

• If at room temperature and pressure (RTP), use the equation n=V/24 where V is volume in dm^3
• If not at RTP, rearrange the ideal gas law PV= nRT and plug in numbers for R (8.31), T in kelvin, P in pascals and V in m^3

Question 3

What is used to accurately measure the mass?

Answer 3

A digital balance that records mass to two decimal places

Question 4

CuCO3 reacts with HCl to produce 15 moles of CO2. How many moles of CuCO3 reacted?

Answer 4

CuCO3 + 2HCl -> CuCl2 + H2O + CO2
Ratio of CuCO3: CO2 is 1:1
15 moles of CuCO3 reacted

Question 5

How could you find percentage mass of CuCO3 in CuCO3.Cu(OH)2?

Answer 5

1. Record mass of CuCO3.Cu(OH)2
2. React with acid and measure volume of CO2 collected. Use this to work out moles of CO2 produced (moles= volume (dm^3) /24)
3. Use ratio in chemical equation to find moles of CuCO3 that reacted
4. Calculate mass of CuCO3
5. Calculate percentage mass of CuCO3 in original sample:
   (mass of CuCO3/ mass of CuCO3.Cu(OH)2) x100

Question 6

Why is it important to rapidly put the bung into conical flask after adding sulfuric acid to CuCO3.Cu(OH)2?

Answer 6

The reaction starts as soon as the acid is added so CO2 will start to be produced. To reduce amount of CO2 that escapes, the bung should be inserted rapidly.

Question 7

Give 3 possible sources of error when investigating volume of gas produced in a reaction

Answer 7

• Some gas could have escaped before the bung was put into conical flask
• Reaction may be incomplete
• Some gas may dissolve in the water meaning a smaller volume would be collected than was released

Question 8

What safety precaution should be taken when conducting an experiment with CuCO3.Cu(OH)2 and H2O?

Answer 8

-CuCO3.Cu(OH)2 is harmful is swallowed so avoid putting it near your face and wash hands after use. It is also an irritant so wear safety goggles and avoid contact with skin.
-H2SO4 causes skin and eye irritation so we wear safety goggles and avoid contact with skin.