The table shows the atomic information recorded by a recycling laboratory for metals in a mixed batch. Before sorting, the objects are washed with water. A ...
Question 1 Report
The table shows the atomic information recorded by a recycling laboratory for metals in a mixed batch. Before sorting, the objects are washed with water. A small mass of magnesium is then tested with dilute acid at room temperature. This reaction produces hydrogen gas and a magnesium chloride solution. The batch also contains iron, aluminium, copper, carbon dust and some iron oxide. Sodium sulfate solution is used in a separate cleaning process.
Table 1 gives information about aluminium and magnesium atoms. Each blank box represents one answer.
| element | symbol | atomic number | number of protons | number of electrons | electronic configuration |
|---|---|---|---|---|---|
| aluminium | □ | 13 | 13 | 13 | □ |
| magnesium | Mg | □ | □ | 12 | 2.8.2 |
(a) Complete the five boxes in Table 1. [5]
(b) Calculate the number of neutrons in an aluminium-27 atom. [2]
(c) State the group and the period of magnesium in the periodic table. [2]
(d) Explain why a magnesium atom forms an Mg2+ ion during a reaction. [3]
(e) Write the formula of magnesium oxide and the formula of aluminium sulfate. Explain how the charges on the ions give the formula of aluminium sulfate. [5]
Answer Details
(a) The five entries are:
| Element | Symbol | Atomic number | Protons | Electrons | Electronic configuration |
|---|---|---|---|---|---|
| aluminium | Al | 13 | 13 | 13 | 2.8.3 |
| magnesium | Mg | 12 | 12 | 12 | 2.8.2 |
Atomic number equals proton number; a neutral atom has equal numbers of protons and electrons. [5]
(b) Neutrons \(=\) mass number \(-\) atomic number:
\[27-13=14\]
14 neutrons. [2]
(c) Magnesium is in group 2 [1] and period 3. [1] [2]
(d) Magnesium has two outer-shell electrons. [1] It loses two electrons [1] and forms an \(\mathrm{Mg^{2+}}\) ion with a stable full outer shell. [1] [3]
(e) Magnesium oxide is \(\mathrm{MgO}\). [1] Aluminium sulfate is \(\mathrm{Al_2(SO_4)_3}\). [2] Aluminium ions are \(\mathrm{Al^{3+}}\) and sulfate ions are \(\mathrm{SO_4^{2-}}\). [1] Two aluminium ions give total charge \(+6\), while three sulfate ions give \(-6\), making the compound neutral. [1] [5]
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