3. (a) Which of the following is the formula of a cation? Put a cross (X) in the box next to your answer - Edexcel - GCSE Chemistry - Question 3 - 2015 - Paper 1

To test for the presence of carbonate ions, add dilute hydrochloric acid to the solution. If carbonate ions are present, effervescence will occur due to the release of carbon dioxide. This can be confirmed by passing the gas through limewater, which will turn cloudy. Additionally, the white precipitate indicates the formation of barium sulfate.

1. Filter the mixture: Use a filter paper and funnel to separate the solid barium sulfate from the liquid. Pour the mixture through the filter, collecting the filtrate in a beaker below.

2. Wash the solid: Rinse the barium sulfate residue on the filter paper with distilled water to remove impurities.

3. Dry the solid: Transfer the barium sulfate to a clean drying oven or allow it to air dry on a clean, dry surface.

Magnesium has an electronic configuration of 2.8.2 and loses two electrons to achieve a stable electron configuration, forming a Mg^2+ ion. In contrast, oxygen has an electronic configuration of 2.6 and gains two electrons to fill its outer shell, forming an O^2- ion. The electrostatic attraction between these oppositely charged ions results in the formation of magnesium oxide, MgO.

The relative formula mass of magnesium oxide (MgO) can be calculated as follows:

• Atomic mass of magnesium (Mg) = 24
• Atomic mass of oxygen (O) = 16

Thus, the relative formula mass is: $24 + 16 = 40$

Therefore, the relative formula mass of MgO is 40.