Question-1[(a) (i)] :2022-may-Chemistry_paper_2__TZ1_SL
Topic:
Given: When heated in air, magnesium ribbon reacts with oxygen to form magnesium oxide.
Discuss: Write a balanced equation for the reaction that occurs.
Answer/Explanation
Solution:
The balanced chemical equation for the reaction between magnesium and oxygen can be written as:
$2 \mathrm{Mg}(\mathrm{s})+\mathrm{O} _2(\mathrm{~g}) \rightarrow 2 \mathrm{MgO}(\mathrm{s})$
This equation shows that two atoms of magnesium $(\mathrm{Mg})$ react with one molecule of oxygen gas $(\mathrm{O} _2)$ to form two molecules of magnesium oxide $(\mathrm{MgO})$ in solid state.
Question-1[(a) (ii)] :2022-may-Chemistry_paper_2__TZ1_SL
Topic:
Discuss: State the block of the periodic table in which magnesium is located.
Answer/Explanation
Solution:
Magnesium (Mg) is located in the second block (s-block) of the periodic table. It is in group 2 (formerly known as group IIA) along with other alkaline earth metals such as beryllium (Be), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).
Question-1[(a) (iii)] :2022-may-Chemistry_paper_2__TZ1_SL
Topic:
Discuss: Identify a metal, in the same period as magnesium, that does not form a basic oxide.
Answer/Explanation
Solution:
In the same period as magnesium (period 3), the metal aluminum $(\mathrm{Al})$ is another commonly known metal that does not form a basic oxide. Instead, aluminum reacts with oxygen to form aluminum oxide $(\mathrm{Al_2O_3})$, which is amphoteric and can behave as both an acid and a base.
Question-1[(b) (i)] :2022-may-Chemistry_paper_2__TZ1_SL
Topic:
Given: The reaction in (a)(i) was carried out in a crucible with a lid and the following data was recorded:
Mass of crucible and lid $=47.372 \pm 0.001 \mathrm{~g}$
Mass of crucible, lid and magnesium ribbon before heating $=53.726 \pm 0.001 \mathrm{~g}$
Mass of crucible, lid and product after heating $=56.941 \pm 0.001 \mathrm{~g}$
Calculate: the amount of magnesium, in mol, that was used.
Answer/Explanation
Solution:
To calculate the amount of magnesium used in the reaction, we need to first determine the mass of magnesium used. We can do this by subtracting the mass of the crucible and lid from the mass of the crucible, lid, and magnesium ribbon before heating:
mass of magnesium = (mass of crucible, lid, and Mg) – (mass of crucible and lid)
mass of magnesium $=(53.726 \pm 0.001 \mathrm{~g})-(47.372 \pm 0.001 \mathrm{~g})$
mass of magnesium $=6.354 \pm 0.002 \mathrm{~g}$
Next, we can use the molar mass of magnesium to convert the mass of magnesium used to moles of magnesium:
molar mass of $\mathrm{Mg}=24.31 \mathrm{~g} / \mathrm{mol}$
moles of $\mathrm{Mg}=\frac{(\mathrm{mass~ of~ Mg})}{(\mathrm{molar~ mass ~of~ Mg})}$
moles of $\mathrm{Mg}=\frac{(6.354 \pm 0.002 \mathrm{~g}) }{(24.31 \mathrm{~g} / \mathrm{mol})}$
moles of $\mathrm{Mg}=0.2613 \pm 0.0001 \mathrm{~mol}$
Therefore, the amount of magnesium used in the reaction is $0.2613 \pm 0.0001 \mathrm{~mol}$.
Question-1[(b) (ii)] :2022-may-Chemistry_paper_2__TZ1_SL
Topic:
Discuss: Determine the percentage uncertainty of the mass of product after heating.
Answer/Explanation
Solution:
The mass of product can be calculated by subtracting the mass of the crucible and lid from the mass of the crucible, lid, and product after heating:
mass of product $=$ (mass of crucible, lid, and product $)$ ( (mass of crucible and lid)
mass of product $=(56.941 \pm 0.001 \mathrm{~g})-(47.372 \pm 0.001 \mathrm{~g})$
mass of product $=9.569 \pm 0.002 \mathrm{~g}$
The absolute uncertainty in the mass of product is $\pm 0.002 \mathrm{~g}$.
The percentage uncertainty can be calculated using the formula:
percentage uncertainty $=(\frac{\mathrm{absolute~ uncertainty }}{\mathrm{ measured ~value}}) \times 100 \%$
percentage uncertainty $=(\frac{2 \times 0.001 \mathrm{~g}}{ 9.569 \mathrm{~g}}) \times 100 \%$
percentage uncertainty $=0.0209 \times 100 \%$
percentage uncertainty $=0.02 \%$
Therefore, the percentage uncertainty of the mass of product after heating is $0.02 \%$.