Hydrocarbons and stuff

Question 1

Define a hydrocarbon.

Answer 1

Compounds that contain only hydrogen atoms and carbon atoms.

Question 2

Describe what is meant by a homologous series.

Answer 2

A homologous series is a family of hydrocarbons that all share the same general formula and have similar chemical properties.

Question 3

What is the general formula for alkanes?

Answer 3

Cn H2n+2

Question 4

What is the general formula for alkenes?

Answer 4

Cn H2n

Question 5

Why is there no such thing as methene?

Answer 5

All alkenes must have a carbon-carbon double bond, so to do this they must have at least two carbon atoms. As ‘methene’ would mean that there would only be one carbon atom present, a double bond would not be possible and thus it does not exist.

Question 6

State the general formula for alkenes.

Answer 6

Cn H2n

Question 7

Describe what is meant by a functional group.

Answer 7

A functional group is an atom, group of atoms or type of bond in a molecule that is responsible for the characteristic reactions of the substance.

Question 8

What is the functional group in alkenes?

Answer 8

The carbon-carbon double bond.

Question 9

What is an addition reaction?

Answer 9

When an atom or group of atoms combine with a molecule to form a larger molecule, with no other product.

Question 10

Explain how unknown substances can be tested for unsaturation.

Answer 10

Alkenes are unsaturated molecules able to take part in addition reactions, whereas alkanes, saturated molecules, are not. This can be tested with an addition reaction between alkenes and bromine water - if alkenes are present, they should react with bromine due to their functional group allowing them to partake in the reaction, and form a colourless dibromo substance as a product.
Thus, a colour change should occur - unsaturated molecules decolourize bromine water.

Question 11

What substances are formed as a result of complete combustion?

Answer 11

Carbon dioxide and water.

Question 12

What substances are formed as a result of incomplete combustion?

Answer 12

Water, carbon particles and carbon monoxide.

Question 13

What is needed for hydrocarbons to undergo complete combustion?

Answer 13

A sufficient supply of oxygen.

Question 14

Describe what is meant by a saturated hydrocarbon.

Answer 14

Saturated hydrocarbons have carbon atoms that are all joined together by single covalent bonds.

Question 15

What kind of reaction is combustion?

Answer 15

An oxidation reaction.

Question 16

State the general formula for alcohols.

Answer 16

Cn H2n+1 OH

Question 17

What is the functional group for alcohols?

Answer 17

• OH, the hydroxyl group.

Question 18

Give some properties of alcohols.

Answer 18

• Flammable
• Oxidised to form carboxylic acids
• Soluble, can be dissolved in water, resulting in a neutral pH

Question 19

Why are alcohols so flammable?

Answer 19

They are able to undergo complete combustion.

Question 20

Why are alcohols used as solvents instead of water?

Answer 20

They are able to dissolve things that water cannot- for exame, hydrocarbons and lipid compounds.

Question 21

Give three uses of alcohols.

Answer 21

• Fuels
• Solvents
• Beverages

Question 22

How come alcohols are able to undergo different chemical reactions to alkenes?

Answer 22

They have a different functional group that allows them to partake in different reactions - for example, oxidation to form carboxylic acids.

Question 24

State the functional group for carboxylic acids.

Answer 24

-COOH. The carboxyl group.

Question 25

Give the general formula for carboxylic acids.

Answer 25

CnH2n+1COOH

Question 26

State the chemical formula for butanoic acid.

Answer 26

C3H7COOH

Question 27

How are carboxylic acids formed?

Answer 27

They are the product of the oxidation of alcohols.

Question 28

What is the oxidising agent used in the oxidation of alcohols to carboxylic acids?

Answer 28

Acidified Potassium Permanganate.

Question 29

Give the chemical formula for potassium permanganate.

Answer 29

KMnO4

Question 30

When an alcohol is oxidised, what is the colour change?

Answer 30

The solution turns from purple to colourless/very pale pink.

Question 32

When oxidising alcohols with acidified potassium Permanganate, what should a student take caution with?

Answer 32

- alcohols are very flammable, so keep it away from sources of heat. - The solution is corrosive and potassium Permanganate can stain, so keep away from skin. - Wear goggles throughout the experiment and stir carefully, as the reaction can be violent.

Question 33

Name the type of monomers that forms proteins.

Answer 33

Amino acids.

Question 34

What is an addition reaction?

Answer 34

Two molecules of the same functional group react together to form a larger molecule, with no other product.

Question 35

What is a condensation reaction?

Answer 35

A carboxylic acid and a dialcohol react together to form another, larger molecule, releasing a small molecule in the process, which is usually water.

Question 36

What are some advantages and disadvantages of using hydrogen fuel cells?

Answer 36

A: - Only waste product is water, which is pure and drinkable. No fossil fuels are burned. - Do not become less efficient over time - It will produce electricity so long as hydrogen is provided. D: - Hydrogen is dangerous to store and work with, as it is an explosive gas. - Generates a low potential difference, so several fuel cells are all needed together.

Question 37

What reaction takes place in a hydrogen fuel cell?

Answer 37

In a hydrogen fuel cell, hydrogen gas will react with either air or pure oxygen, producing water. 2H2 + O2 ---> 2H2O

Question 38

What element is being oxidised at the cathode? What charge does the cathode have IN HYDROGEN FUEL CELLS FOR SOME FUCKING REASON

Answer 38

The cathode (in h.f.c.) is positively charged. O2 + 4H + 4e ----> 2H2O

Question 39

What is the functional group of esters?

Answer 39

Carbon double bond O and single bond O C--O - O COO

Question 40

Which homologous groups are needed to create esters?

Answer 40

Dialcohols and carboxylic acids.

Question 41

What is made when ethanol and ethanoic acid are combined?

Answer 41

Ethyl ethanoate.

Question 42

What sort of catalyst is needed in the reaction to make ethyl ethanoate?

Answer 42

Sulfuric acid.

Question 43

What kind of bonds do polymers have?

Answer 43

Weak intermolecular forces between molecules. Strong covalent bonds between atoms within those molecules.