2019 A Level H2 Chemistry Paper 1 Question 4 - Deduce Dot-Cross Diagram for Barium Peroxide

Let Chemistry Guru, Singapore's renowned JC Chemistry tuition centre, guide you through 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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