Transition Elements

Reactions with Alkenes

This topic is part of F322 AS OCR A Chemistry. There are five different reactions that you need to know involving the reaction with alkenes.

I have summarised all the reactions in this diagram/mind map I made below:

 

 

1. Reaction with halogens/ Halogen addition reactions

 

- Electrophilic Addition

- This is a test for unsaturation.

- The observation: decolourisation.

- Unsaturated hydrocarbons decolourise bromine water.

 

2. Reaction with a halogen halide

 

- e.g. HCl

- Electrophilic Addition

 

3. Reaction with Hydrogen / Hydrogenation

 

- A Nickel (Ni) Catalyst is used

- Requires High temperatures and pressures (About 150°C)

- Used in the manufacture of margarine from animal or vegetable fats and oils.

 

4. Reaction with water

 

- The water must be in gaseous state - H₂O (g) - Steam

- High Temperatures

- Catalyst: Phosphoric Acid (H₃PO₄)

- Product: An Alcohol

 

5. Addition Polymerisation

 

- Many monomers (unsaturated), bond together by the double bond.

- The double bond opens up and joins to other monomers to form ONE large molecule called a POLYMER.



Come and Practice some Questions!

Hi to My Chemistry Club friends,

Today I am going to go over some common exam questions and in response there will be some model answers. I hope this helps get you ready for your F321 OCR A Chemistry exam, or just enlightens your chemistry knowledge :)

1. Define the term: Relative Atomic Mass? (3)

Relative Atomic Mass is the average mass of an atom compared to 1/12th the mass of an atom of carbon-12.

2. What is meant by an orbital? (1)

An orbital is a region that can hold up to two electrons with opposite spins.

3. MgCO₃ (s) --> MgO (s) + CO₂ (g)

    What type of reaction is this? (1)

Thermal Decomposition

4. The student did an experiment another three times, using CaCO₃, SrCO₃ and BaCO₃. What trend in the behaviour of the group 2 carbonates would be observed by the student? (1)

The ease of thermal decomposition decreases down the group.

 

5. Explain why NF₃has a permanent dipole? (2)

F Is more electronegative than N. Also the dipoles do not cancel out (as it is an asymmetrical shape).

6. Explain, in terms of the intermolecular forces present, why ICl has a higher boiling point than Cl₂? (2)

ICl has permanent dipole-dipole interactions and Cl₂ has only Van-der-Waals' forces. The forces are stronger in ICl and this is why it has a higher boiling point.

7. The hydrazine molecule, H₂N-NH₂, is covalent. Predict the H-N-H bond angle in a hydrazine molecule. Explain your answer. (4)

107 °

There are 3 bonding pairs and 1 lone pair. The electron pairs repel. However, the lone pairs repel more than the bonded pairs.

8. What is the name for NaClO? (1)

Sodium Chlorate (I)

[suffix -ate just means the chlorine has oxygen attached to it]

9. What is meant by the term electronegativity? (2)

It is the ability of an atom to attract electrons in a covalent bond.

10. Describe how Van-der-Waals' forces arise. (3)

There is an uneven distribution of electrons, this creates an instantaneous dipole. This then causes induced dipoles in neighbouring molecules.

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Here is a diagram to help explain question 10:

 

 

 

 

 

 

 

 

 

 

Thanks for reading today's blog post, but don't forget to subscribe so you do not miss any of my regular future posts!

Holly :)

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Here is a little bonus question:

State and explain the trend in the boiling points of chlorine, bromine and iodine. (3)

Chlorine has the lowest boiling point, followed by bromine and then iodine has the highest boiling point.

There is a greater number of electrons/stronger Van-der-Waals' forces in Iodine compared to Chlorine.

Therefore more energy is needed to break the Van-der-Waals' forces.