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9.38

9 .39


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Answer 1

Answer:

Explanation:

To make a gallon of 3% peroxide: In a clean gallon container, combine 1 and ¼ cups of 35% food grade hydrogen peroxide with 14 and ¾ cups of water. To make 3% hydrogen peroxide from 35% hydrogen peroxide, the general mixing guideline is: 1 part 35% hydrogen peroxide plus 11 parts water = 3% hydrogen peroxide.

Hydrogen peroxide is used to restore the colour of old oil paintings containing lead oxide. ... Now, when the painting is dipped in a dilute solution of H2O2 for some time, lead sulphide is slowly oxidised to white lead sulphate. Thus the colour of lead painting is restored.

The white pigment in old painting turns black due to formation of PbS.This white pigment is restored by using hydrogen peroxide.The reaction is as follows:

H2O2(aq) + PbS(s) →PbSO4(s) + H2O(l)             white pigment

Answer 2

Question 9.38

Hydrogen peroxide is a combination of hydrogen and oxygen.The foam is oxygen bubbles.

The liquid contains oxygen and hydrogen molecules. It is an oxidizing agent, which means that it can kill living cells, such as bacteria.

Different strengths, or concentrations, of hydrogen peroxide are available, depending on its intended use. High concentrations are typical in industrial production. The most common concentration sold for household use is 3 percent.

Hydrogen peroxide is safe for most people if they use it correctly. However, the compound can be harmful if a person uses it too often or if the concentration is too strong.

Hydrogen peroxide is already found in concentrated form. 3% of concentration is safe to use but hydrogen peroxide which has a concentration of 35% can lead to severe problems.

That is why dilution of hydrogen peroxide is important. As dilute hudrogen peroxide is safe to use.

But if a dilute solution of hydrogen peroxide is needed to be concentrated it cannot be done by strong heating. Never concentrate H2O2 by strong heating as it breaks into hydrogen and oxygen gas instead of making a concentrated solution.

Question 9.39

When an oil painting is constantly exposed to the atmosphere, the traces of hydrogen sulphide gas present in the atmosphere slowly blackens the the painting converting lead oxide (white) to lead sulphide (black).

PbO + H2S -> PbS + H2O

(white) (black)

Now, when the painting is dipped in a dilute solution of H2O2 for some time, lead sulphide is slowly oxidised to white lead sulphate.

PbS + 4H2O2 -> PbSO4 + 4H2O

Thus the colour of lead painting is restored.

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