3.6 & 3.7 Recall that alkenes have the general formula CNH2N

Take a photo of it and upload to your blog (see sample below)

4. What is the general formula for alkenes?
CNH2N

5. Describe and explain the trend in boiling point
The boiling point increases as there stronger intermolecular forces that require more energy to be broken

6. Explain why there is no such compound as methene
To be classified as an alkene it requires at least one double bond

7. How do you quickly identify from the displayed formula that the hydrocarbon is unsaturated?
Check the general formula that it is not CNH2N+2(i.e. does not only include single bonds)

3.5 I can recall the reaction of methane and bromine

       Alkanes react with bromine in the presence of UV light

·         Explain why this condition is necessary

UV light is needed to supply the energy to break the covalent bonds between hydrogen and carbon

3.       What is this type of reaction called

substitution reaction

4.       State and explain the observations

It would turn from brown to colourless. This is because the concentration of the brown bromine molecule decreases while the concentrations of the product increase (colourless).

5.       Draw the displayed formula of the reaction between methane and bromine (upload a photo)

6.       Write out a balanced (with state symbols) the reaction between ethane and chlorine
C₂H_6 (l)+ Cl_2(g) -> C₂H₅Cl(l) + Hcl (aq)

7.       State and explain the observations in this chemical reaction

It turns from green to colourless. The reactants (chlorine) are green and the products (ethanechloride and hydrochloric acid) are colourless. This is a substitution reaction where the concentration of  the green chlorine molecule decreases and the colourless products increase.

3.4 Recall the products of the complete and incomplete combustion of alkenes

1.       Saturated hydrocarbons are called alkanes

2.       Small chain alkanes are used as fuels

3.       The reaction is called combustion

4.       The word equation for  this chemical reaction is :

fuel (alkane) + oxygen → water + carbon dioxide+ ENERGY (heat, light, sound)

5.       If there is insufficient oxygen then the word equation is:

fuel (alkane) + oxygen → carbon monoxide + water + ENERGY (heat, light, sound)

6.       The problem with this reaction is that carbon monoxide is produced this gas is toxic to the human body (see objective 5.11)

7.       Where can you find incomplete combustion?

In car engines or in your house when you burn fire.

8.       What is used to reduce the harmful products from incomplete combustion?

Use a catalytic converter to convert CO to CO₂9.       During incomplete combustion a smoky flame is often seen, explain this observation

Extn: write a balanced equation (with state symbols) for the combustion of propane gas
This is soot which is formed by unburnt carbon

C₃H₈  + 5O_2    à  3CO₂ + 4H₂O

3.2 and 3.3 I can recall the general formula and the displayed formulae for alkenes

NOTE: answers are in white

What is the general formula for alkanes?

C(n)H(2n)

Describe and explain the trend in boiling point.

The boiling point increases as you go down the group. This is because the molecules get larger and their are more intermolecular forces to break.

  

3.1 I can explain terms homologous series, hydrocarbon, saturated, unsaturated, general formula, and isomerism

NOTE: answers in white

Term	Definition	Example
Homologous series	a family of hydrocarbons with the same general formula	alkanes
Hydrocarbon	a compound containing only carbon and hydrogen	crude oil
Saturated hydrocarbon	a hydrocarbon which only contains single bonds	alkane
Unsaturated hydrocarbon	a hydrocarbon that contains at least one double bond	alkene
General formula	a mathematical equation that shows the ratio of the different atoms (i.e. carbon and hydrogen)	C(n)H(2n)
Isomerism	Hydrocarbons with the same general formula but with a different structure

5.13 I can describe the catalytic cracking of long chain hydrocarbons

1) define the term catalyst
A catalyst is a substance that changes the rate of a reaction (e.g. silica, liver, manganese dioxide) usually speeding it up but it can also slow down reactions like rust.

2)Why is a catalyst used?
It is used to speed up the reaction

3)why are high temperatures needed?
High temperatures are needed to break down the bonds of the long chain hydrocarbons and as a by product will also speed up the reaction.



NOTE: answers are in white colour

1)Why does liquid paraffin need to be broken down?
There is to many long chain molecules and not enough short chain molecules like kerosine which are more useful
2)What is the name of the process used to break down paraffin? Describe how it works.
Cracking- it involves the heating of long chain hydrocarbons with the influence of catalyst
3)How do you collect the gas produced?
You must collect under water as it is insoluble
4)What is the name of the catalyst used?
Ceramic catalyst - broken pot
5)What are the safety precautions of the experiment?

Do not let the water setback otherwise it turns into steam and can cause an explosion 

6)Why does the pot turn black?

It interacts with the inorganic molecules

7)What else is formed as a product of the experiment?

Smoky residue

8)Why is it important to keep heating?
If you stop the gas will start to cool and water may enter the apparatus through the bunsen valve

5.12 I can recall the problems associated with the fractional distillation of crude oil

1) when crude oil undergoes fractional distillation, there are to many long chain hydrocarbons (e.g. bitumen) produced and not enough short chain molecules (e.g. kerosine)

2) To solve these problems the long chain molecules undergo a chemical reaction called cracking

5.11 I can recall how nitrogen oxides are formed in car engines

1)Write the general equation for the combustion of a fuel
fuel + oxygen --> carbon dioxide + water + energy

2)During combustion the nitrogen in air can react to form what gases?
The nitrogen combust to from NOX gases

3) What condition is necessary for the formation of these gases?
Extremely high temperatures are needed for the formation of these gases

4)  In what common object is this condition found?
a car engine

5) Why is this condition needed for nitrogen to react?
Nitrogen molecules are bonded together with a triple covalent bond and are therefore inert. High temperatures are needed to break this strong bond

6)  What are the dangers of the products from this reaction?
You may be subjected to asthma and other diseases. It can also produce acid rain which is corrosive.

5.10 I can recall the problems associated with incomplete combustion

1)What are the properties of carbon monoxide?

It is a colourless, odorless, poisonous gas that has a strong affinity towards haemoglobin.

2)Carbon monoxide is formed when a hydrocarbon is burned in an insufficient supply of oxygen.
3)Carbon monoxide is poisonous because it will bond with the haemoglobin in your blood and stop your blood from carrying oxygen around your body.

5.6 I can recall what crude oil is made from

a. Define the word hydrocarbon….	a compound containing only hydrogen and carbon
b. What is crude oil made from?	formed from tiny animals and plants that lived in the sea
c.       Define the word compound….	two or more elements chemically combined
d.      Define the word mixture…..	two or more substances physically combined

 NOTE:Answers in white font

. How long does crude oil take to make?	150 million years
e. Where does the energy in crude oil originally come from?	sun light
f. How is crude oil different from coal?	crude oil is liquid while coal is solid and is not a hydrocarbon
g. Crude oil, coal and natural gas are collectively known as _________ fuels	fossil
h. How is crude oil transported when it is extracted from the ground?	by pipeline or by oil tanker

5.9 I can describe the trend in boiling point and viscosity of the main fractions

1)What is the trend in boiling point of the fractions?

The volatile substances with lower boiling points rise to the top of column and the substances with higher boiling points are collected at the bottom. The boiling points are in ascending order from top to bottom in the column. In the test tube diagram above, the boiling point of the substances decreases from left to right.  In general, the larger the molecule, the higher its boiling point.

2)Define viscosity.

Viscosity is a measure of the resistance of a fluid which is being deformed by shear or tensile stress.
Source: www.wikipedia.com 

3)  What is the trend in viscosity of the fractions?

In general, the larger the molecule, the higher the viscosity. As you know, large molecules have higher boiling points because there are more bonds to break. Therefore, the viscosity decreases as you go up the column. In the diagram above, the viscosity of the fractions decrease from left to right.

4)What is the trend in colour of the fractions?

The colour of the fractions become darker as you go up the column. In the diagram above, the colour gets darker from right to left. In general, the larger, more viscous the molecule,  the darker its colour.

5)Why is crude oil separated into fractions?

Crude oil itself is a useless substance and therefore it is separated through fractional distillation to form other useful substances.  

6)What process is used to separate crude oil into fractions?

Crude oil is separated by a process called fractional distillation in which the different boiling points of the unique substances allow it to be separated into fractions. The substances with the lowest boiling point at the top and the substance with the highest boiling point at the bottom.  

7) What physical property allows this process to work?

It has different boiling points.

 

5.8 I can recall the names and uses of the main fractions obtained from crude oil

click on the image to see the answers

5.7 I can describe how crude oil is separated