A technician checks the purity of magnesium metal used to make lightweight bicycle components. Table 1 gives information for the three naturally occurring m...
Question 1 Report
A technician checks the purity of magnesium metal used to make lightweight bicycle components. Table 1 gives information for the three naturally occurring magnesium isotopes. Each species is a neutral atom.
| Isotope | Number of protons | Number of neutrons | Relative abundance / % |
|---|---|---|---|
| magnesium-24 | 12 | 12 | 78.99 |
| magnesium-25 | 12 | 13 | 10.00 |
| magnesium-26 | 12 | 14 | 11.01 |
The metal is later reacted with dilute acid to produce hydrogen gas. The isotope does not change which element the atom is.
(a) Name the particles in an atom that have a positive charge. [1]
(b) Give the mass number of a magnesium-25 atom. [1]
(c) Complete the electronic configuration of a magnesium atom: 2, 8, ________. [1]
(d) Calculate the relative atomic mass of magnesium using Table 1. Give your answer to two decimal places. [3]
(e) Explain why magnesium-24 and magnesium-26 have similar chemical properties. [2]
(f) State the charge on a magnesium ion formed when a magnesium atom loses two electrons. [1]
(g) Give the formula of magnesium chloride. [1]
Answer Details
(a) Protons have a positive charge. [1]
(b) Magnesium-25 has mass number 25. [1]
(c) Magnesium has 12 electrons arranged \(2,8,\boldsymbol{2}\). [1]
(d) \[\frac{(24\times78.99)+(25\times10.00)+(26\times11.01)}{100}=24.3202\] To two decimal places, the relative atomic mass is 24.32. [3]
(e) Magnesium-24 and magnesium-26 have the same number of electrons and the same outer-shell electron arrangement. Chemical properties depend mainly on outer-shell electrons, not neutron number. [2]
(f) Losing two electrons forms an ion with charge \(2+\). [1]
(g) Magnesium chloride is \(\mathrm{MgCl_2}\). One \(\mathrm{Mg^{2+}}\) ion needs two \(\mathrm{Cl^-}\) ions for an overall neutral compound. [1]
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