2 (a) The formula of an aluminium ion is Al$^{3+}$ - Edexcel - GCSE Chemistry - Question 2 - 2017 - Paper 1
Question 2
2 (a) The formula of an aluminium ion is Al$^{3+}$.
The formula of a sulfate ion is SO$_4^{2-}$.
(i) Which of the following is the correct formula of aluminium ... show full transcript
Worked Solution & Example Answer:2 (a) The formula of an aluminium ion is Al$^{3+}$ - Edexcel - GCSE Chemistry - Question 2 - 2017 - Paper 1
Step 1
Which of the following is the correct formula of aluminium sulfate?
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Answer
The correct formula for aluminium sulfate is B Al2(SO4)3. This formula indicates that two aluminium ions combine with three sulfate ions.
Step 2
Give the names of the two solutions that are added.
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Answer
To test for sulfate ions, the two solutions that are typically added are:
Barium chloride (BaCl2) - it reacts with sulfate ions to produce barium sulfate, which is a white precipitate.
Hydrochloric acid (HCl) - it helps to provide an acidic environment and ensures the precipitation of barium sulfate.
Step 3
Which of these substances is insoluble in water?
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Answer
The substance that is insoluble in water is C lead sulfate. Lead sulfate does not dissolve well in water compared to the other options.
Step 4
Describe how calcium and oxygen atoms react to form calcium and oxide ions.
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Answer
Calcium (Ca) has the electronic configuration of 2.8.8, meaning it has two electrons in its outer shell. To achieve a stable electronic configuration, calcium loses these two electrons and forms a Ca2+ ion. Oxygen (O), with an electronic configuration of 2.6, has six electrons in its outer shell. It gains two electrons to complete its outer shell and forms an O2− ion.
In the reaction, the transfer of electrons occurs:
Calcium loses 2 electrons:
ightarrow ext{Ca}^{2+} + 2e^-$$
- Oxygen gains 2 electrons:
$$ ext{O} + 2e^-
ightarrow ext{O}^{2-}$$
Thus, calcium forms a cation and oxygen forms an anion, resulting in the formation of the ionic compound calcium oxide (CaO). Diagrams can further illustrate the electron transfer and the formation of ions.
