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Edexcel A Level Chemistry - 2021 MMS EXAMS > Exam Questions > Flashcards

Flashcards in Exam Questions Deck (8)
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1
Q

Phosphorus (III) chloride molecules are pyramidal with a bond angle less than 109.5. Explain why. (2)

A

Pyramidal because there are 3 bonding pairs and one lone pair of electrons on P
Bond angle because lone pair-bond pair repulsion is greater than bond pair-bond pair repulsion

2
Q

Calcium Nitrate decomposes in a similar way to magnesium nitrate, but needs a higher temperature. Explain in terms of the charge and size of the cations. (3)

A

Ca2+ has larger ionic radius
So Ca2+ causes less polarisation
Nitrate ion electron cloud polarised

3
Q

Explain why boiling temperatures increase from chlorine to iodine. (2)

A

Down the group, number of electrons increases

So strength of London forces increases and more energy needed to separate the molecules

4
Q

Explain why zinc ions are colourless (2)

A

Zinc ions have a full 3d subshell

So electrons cannot move between d orbitals/cannot be promoted

5
Q

Explain why the first ionisation energy of magnesium is higher than that of sodium (3)

A

Magnesium has more protons than Sodium, greater effective nuclear charge
Shielding in Magnesium the same as in Sodium
Force of attraction between nucleus and outer electron is greater in Mg

6
Q

Explain why different alkanes in crude oil can be separated by fractional distillation (2)

A

Different alkanes have different boiling temperature

Because of different chain length/strength of intermolecular forces

7
Q

Describe how reactions happen in catalytic converters (3)

A

Adsorption to catalytic surface
Weakenign of bonds on catalytic surface
Desorption of products

8
Q

Give the steps to show have 2,4-DNPH can be used to distinguish between phenylethanone and phenylethanal (4)

A

Formation of yellow/orange precipitate
Filter then recrystallise products
Determination of melting temperature
Comparison and identification from use of database