Some of the blue pigment azurite used by an artist in a picture painted in 1600 has changed over the years into green malachite according to the following balanced equation - Leaving Cert Chemistry - Question a - 2017

To calculate the maximum mass of malachite that forms from 6.89 g of azurite:

• The molar mass of malachite:

  $M_{malachite} = 221 ext{ g/mol}$

• From the balanced equation, we see:

  $2 ext{ moles azurite} \rightarrow 3 ext{ moles malachite}$

• The amount of azurite that corresponds to 6.89 g:

  $0.03 ext{ moles azurite} \rightarrow 0.01 ext{ moles malachite}$

Using stoichiometry:

• The maximum mass of malachite that will form:

  $3 \times \frac{221 ext{ g malachite}}{663 ext{ g azurite}} \times 6.89 ext{ g azurite}$

Calculating gives the maximum mass of malachite as approximately 6.63 g.

To find the volume of carbon dioxide released:

• Use the ideal gas law where 1 mole of gas at standard temperature and pressure (s.t.p.) occupies 22.4 L.

• From the equation, for the amount of malachite formed:

  $689 ext{ g azurite} \rightarrow 663 ext{ g malachite} \rightarrow 0.224 ext{ L CO}_2$

• Determine the moles of malachite:

  $0.01/2 \rightarrow 0.01 ext{ moles CO}_2$

Thus, the volume of carbon dioxide released would be approximately 0.224 L.

To prevent or delay the deterioration of the painting, it is advisable to:

1. Keep it dry to reduce moisture that facilitates the reaction.
2. Maintain low humidity levels to inhibit further reactions.
3. Use a protective coating, such as a water-resistant varnish, to shield it from environmental factors.
4. Protect from heat and direct sunlight to minimize degradation.