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. $$2Cu_2(CO_3)(OH)_2 (s) + H_2O (l) \rightarrow 3CuCO_3(OH)_2 (s) + CO_2 (g)$$ Analysis shows that the only copper-containing pigments in the painting are azurite and malachite and that the picture now contains 3.81 g of copper. (i) What mass of pure azurite contains 3.81 g copper? (ii) Calculate the maximum mass of malachite that will eventually be formed from this mass of azurite? (iii) What is the volume, measured at s.t.p., of carbon dioxide that would be released from the painting in the formation of this mass of malachite? (iv) Suggest a way that further deterioration of the painting by this chemical reaction could be prevented or delayed.

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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

Question (a)

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 e... show full transcript

Worked Solution & Example Answer: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

Step 1

What mass of pure azurite contains 3.81 g copper?

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Answer

To determine the mass of pure azurite containing 3.81 g of copper, we first consider the molar mass of copper, which is approximately 63.55 g/mol. In azurite, which has the formula (Cu_2(CO_3)(OH)_2), there are 2 moles of copper per mole of azurite. Therefore, the mass of azurite corresponding to the copper content can be found using the ratio:

Calculate moles of copper:

$\text{Moles of copper} = \frac{\text{mass of copper}}{\text{molar mass of copper}} = \frac{3.81 g}{63.55 g/mol} \approx 0.0599 \text{ moles of copper}$
Find the moles of azurite from moles of copper:

$\text{Moles of azurite} = \frac{0.0599 \text{ moles of copper}}{2} \approx 0.02995 \text{ moles of azurite}$
Calculate the molar mass of azurite:

The molar mass of azurite is approximately 344.5 g/mol.
Calculate mass of azurite:

$\text{Mass of azurite} = \text{moles of azurite} \times \text{molar mass of azurite} \approx 0.02995 \text{ moles} \times 344.5 g/mol \approx 10.31 g$

Thus, approximately 10.31 g of pure azurite contains 3.81 g of copper.

Step 2

Calculate the maximum mass of malachite that will eventually be formed from this mass of azurite?

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Answer

To calculate the maximum mass of malachite formed from the azurite, we use the balanced chemical equation:

$2Cu_2(CO_3)(OH)_2 (s) + H_2O (l) \rightarrow 3CuCO_3(OH)_2 (s) + CO_2 (g)$

From the equation, 2 moles of azurite yield 3 moles of malachite. Therefore, the stoichiometric ratio of azurite to malachite is:

$\frac{3}{2}$
We previously calculated that we have approximately 0.02995 moles of azurite. Hence, the moles of malachite produced can be calculated as follows:

$\text{Moles of malachite} = 0.02995 \text{ moles of azurite} \times \frac{3}{2} \approx 0.044925 \text{ moles of malachite}$
Calculate the molar mass of malachite, which is approximately 221 g/mol:

$\text{Mass of malachite} = \text{moles of malachite} \times \text{molar mass of malachite} \approx 0.044925 \text{ moles} \times 221 g/mol \approx 9.93 g$

Thus, a maximum of approximately 9.93 g of malachite will be formed.

Step 3

What is the volume, measured at s.t.p., of carbon dioxide that would be released from the painting in the formation of this mass of malachite?

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Answer

To calculate the volume of carbon dioxide released during the formation of malachite, we analyze the balanced equation:

$2Cu_2(CO_3)(OH)_2 + H_2O \rightarrow 3CuCO_3(OH)_2 + CO_2$

From this equation, we see that 2 moles of azurite produce 1 mole of carbon dioxide when converting to malachite.

Calculate the moles of malachite formed:

From the previous calculation, we have 0.044925 moles of malachite.

The moles of carbon dioxide released will be half of the moles of malachite:

$\text{Moles of } CO_2 = \frac{0.044925}{3} \approx 0.014975\text{ moles}\text{ of } CO_2$
Use the molar volume of gas at standard temperature and pressure (s.t.p.), which is approximately 22.4 L/mol:

$\text{Volume of } CO_2 = 0.014975 \text{ moles} \times 22.4 \frac{L}{mol} \approx 0.335 L$

Thus, approximately 0.335 liters of carbon dioxide would be released.

Step 4

Suggest a way that further deterioration of the painting by this chemical reaction could be prevented or delayed.

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Answer

To prevent or delay further deterioration of the painting caused by the reaction converting azurite to malachite, it is recommended to:

Keep it dry and in a low humidity environment: Moisture can facilitate the chemical reaction, so keeping the painting in a controlled environment will help slow down the process.
Use waterproof varnish (coating): Applying a protective coating can limit exposure to moisture and prevent chemical reactions, ensuring the conservation of the painting.
Protect from heat: Excessive heat can also accelerate deterioration, so keeping the painting in a stable temperature environment is essential.

By taking these measures, the longevity of the artwork can be maintained.

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

Worked Solution & Example Answer: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

What mass of pure azurite contains 3.81 g copper?

Calculate the maximum mass of malachite that will eventually be formed from this mass of azurite?

What is the volume, measured at s.t.p., of carbon dioxide that would be released from the painting in the formation of this mass of malachite?

Suggest a way that further deterioration of the painting by this chemical reaction could be prevented or delayed.

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