The oxides of nitrogen, \(\mathrm{NO}\) and \(\mathrm{NO_2}\), act as pollutants in the Earth’s atmosphere in a number of different ways.
Three statements about the oxides of nitrogen are listed.
1 They react with oxygen and water vapour to form nitric acid, a constituent of acid rain.
2 They react with carbon monoxide to form photochemical smog.
3 They catalyse the oxidation of sulfur dioxide in the formation of sulfuric acid, another constituent of acid rain.
Which statements are correct?
Correct Answer: \( \boxed{\mathrm{C}} \)
Statement 1 is correct because nitrogen oxides react with oxygen and water to form nitric acid, contributing to acid rain.
Statement 2 is incorrect because photochemical smog is formed mainly when nitrogen oxides react with unburnt hydrocarbons in the presence of sunlight, not carbon monoxide.
Statement 3 is correct because nitrogen oxides catalyse the oxidation of sulfur dioxide to sulfur trioxide, which forms sulfuric acid.
Therefore, the correct answer is (C).
Magnesium nitrate, \(\mathrm{Mg(NO_3)_2}\), will decompose when heated to give a white solid and a mixture of gases. One of the gases released is oxygen.
\(29.7\,\mathrm{g}\) of anhydrous magnesium nitrate is heated until no further reaction takes place.
Which mass of oxygen is produced?
Correct Answer: \( \boxed{\mathrm{A}} \)
Thermal decomposition:
\(\mathrm{2Mg(NO_3)_2\rightarrow2MgO+4NO_2+O_2}\)
Molar mass of \(\mathrm{Mg(NO_3)_2}\):
\(\mathrm{24.3+2(14+3\times16)=148.3\,g\,mol^{-1}}\)
Moles of \(\mathrm{Mg(NO_3)_2}\):
\(\mathrm{\dfrac{29.7}{148.3}\approx0.20\,mol}\)
From the equation, \(2\) mol of nitrate produce \(1\) mol of \(\mathrm{O_2}\).
Moles of \(\mathrm{O_2}=0.20\times\dfrac{1}{2}=0.10\,mol\)
Mass of \(\mathrm{O_2}=0.10\times32=3.2\,\mathrm{g}\)
Therefore, the correct answer is (A).
When heated, magnesium nitrate decomposes.
Which equation for the thermal decomposition of magnesium nitrate is correct?
Correct Answer: \( \boxed{\mathrm{C}} \)
Group 2 metal nitrates (except lithium nitrate) decompose on heating to form the metal oxide, nitrogen dioxide and oxygen.
The balanced equation is:
\(\mathrm{2Mg(NO_3)_2\rightarrow2MgO+4NO_2+O_2}\)
Therefore, the correct answer is (C).
