2019 A Level H2 Chemistry Paper 1 Question 4 - Deduce Dot-Cross Diagram for Barium Peroxide
Let's take a look at Paper 1 Question 4.
We need to deduce the dot and cross diagram for barium peroxide.
1. Deduce barium cation
Since barium is a Group 2 metal, it will lose 2 electrons to form Ba2+ cation.
Hence options A and B where Ba has a +1 charge will be eliminated.
2. Deduce peroxide anion
For both options C and D, each oxygen atom has an additional electron (x).
This means peroxide will gain a total of 2 additional electrons and its charge should be a -2.
We can also deduce this from hydrogen peroxide H2O2.
To form peroxide from hydrogen peroxide, we can treat H2O2 as a diprotic acid which donates 2 protons.
Both O-H bonds are broken to release 2 H+, hence the peroxide will have an overall charge of -2.
Therefore the answer to this question will be C.
Topic: Chemical Bonding, Physical Chemistry, A Level Chemistry, Singapore
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