Hydrocarbons and stuff Flashcards
Define a hydrocarbon.
Compounds that contain only hydrogen atoms and carbon atoms.
Describe what is meant by a homologous series.
A homologous series is a family of hydrocarbons that all share the same general formula and have similar chemical properties.
What is the general formula for alkanes?
Cn H2n+2
What is the general formula for alkenes?
Cn H2n
Why is there no such thing as methene?
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.
State the general formula for alkenes.
Cn H2n
Describe what is meant by a functional group.
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.
What is the functional group in alkenes?
The carbon-carbon double bond.
What is an addition reaction?
When an atom or group of atoms combine with a molecule to form a larger molecule, with no other product.
Explain how unknown substances can be tested for unsaturation.
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.
What substances are formed as a result of complete combustion?
Carbon dioxide and water.
What substances are formed as a result of incomplete combustion?
Water, carbon particles and carbon monoxide.
What is needed for hydrocarbons to undergo complete combustion?
A sufficient supply of oxygen.
Describe what is meant by a saturated hydrocarbon.
Saturated hydrocarbons have carbon atoms that are all joined together by single covalent bonds.
What kind of reaction is combustion?
An oxidation reaction.
State the general formula for alcohols.
Cn H2n+1 OH
What is the functional group for alcohols?
- OH, the hydroxyl group.
Give some properties of alcohols.
- Flammable
- Oxidised to form carboxylic acids
- Soluble, can be dissolved in water, resulting in a neutral pH
Why are alcohols so flammable?
They are able to undergo complete combustion.
Why are alcohols used as solvents instead of water?
They are able to dissolve things that water cannot- for exame, hydrocarbons and lipid compounds.
Give three uses of alcohols.
- Fuels
- Solvents
- Beverages
How come alcohols are able to undergo different chemical reactions to alkenes?
They have a different functional group that allows them to partake in different reactions - for example, oxidation to form carboxylic acids.
State the functional group for carboxylic acids.
-COOH. The carboxyl group.
Give the general formula for carboxylic acids.
CnH2n+1COOH
State the chemical formula for butanoic acid.
C3H7COOH
How are carboxylic acids formed?
They are the product of the oxidation of alcohols.
What is the oxidising agent used in the oxidation of alcohols to carboxylic acids?
Acidified Potassium Permanganate.
Give the chemical formula for potassium permanganate.
KMnO4
When an alcohol is oxidised, what is the colour change?
The solution turns from purple to colourless/very pale pink.
When oxidising alcohols with acidified potassium Permanganate, what should a student take caution with?
- 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.
Name the type of monomers that forms proteins.
Amino acids.
What is an addition reaction?
Two molecules of the same functional group react together to form a larger molecule, with no other product.
What is a condensation reaction?
A carboxylic acid and a dialcohol react together to form another, larger molecule, releasing a small molecule in the process, which is usually water.
What are some advantages and disadvantages of using hydrogen fuel cells?
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.
What reaction takes place in a hydrogen fuel cell?
In a hydrogen fuel cell, hydrogen gas will react with either air or pure oxygen, producing water.
2H2 + O2 —> 2H2O
What element is being oxidised at the cathode? What charge does the cathode have IN HYDROGEN FUEL CELLS FOR SOME FUCKING REASON
The cathode (in h.f.c.) is positively charged.
O2 + 4H + 4e —-> 2H2O
What is the functional group of esters?
Carbon double bond O and single bond O
C–O
- O
COO
Which homologous groups are needed to create esters?
Dialcohols and carboxylic acids.
What is made when ethanol and ethanoic acid are combined?
Ethyl ethanoate.
What sort of catalyst is needed in the reaction to make ethyl ethanoate?
Sulfuric acid.
What kind of bonds do polymers have?
Weak intermolecular forces between molecules.
Strong covalent bonds between atoms within those molecules.
