iGCSE Organic Chemistry - DA

1. What is the exact definition of ‘hydrocarbon’?

A chemical compound composed of carbon and hydrogen ONLY (don’t forget the only at the end!)

1. What is fractional distillation?

A separation technique used to separate a mixture of liquids into different fractions by their boiling point.

1. In a fractionating column what is the order of fractions from top to bottom?

Use the first letter of each chemical to make a mnemonic

Refinery gases, gasoline, kerosene, diesel oil, fuel oil, bitumen

1. Give a use for the following fractions: refinery gases, gasoline, kerosene, diesel, fuel oil, bitumen

1. As you go DOWN the fractionating column what is the trend in boiling point and hydrocarbon chain length?

The boiling points of the fractions get HIGHER as you go down the column. The length of the carbon chain gets LONGER as you go down the column

1. As the chain of a hydrocarbon gets longer what happens to intermolecular forces, viscosity and boiling point?

As the hydrocarbon chain gets longer the intermolecular forces increase

As the hydrocarbon chain gets longer the viscosity increases

As the hydrocarbon chain gets longer the boiling point increases

1. What is the definition of boiling point?

The temperature at which a liquid turns into a gas.

1. What is the definition of volatility?

How easily something evaporates

1. What is the definition of viscosity?

How easily something flows

1. What is the definition of flammability?

How easily something burns

1. What is an alkane?

A group of saturated hydrocarbons. E.g. ethane

1. What is the general formula for an alkane?

C_nH_2n+2

1. What is the mnemonic to remember the naming order of the first 4 alkanes?

Monkeys Eat Peanut Butter (Meth, Eth, Prop, But)

1. What is an isomer?

Molecules that have the same molecular formula but different structural arrangement of atoms

1. What is a displayed formula?

Illustrates the arrangement of atoms for each element in space and includes the bonds between atoms e.g.

1. What is a molecular formula?

A formula that shows the actual number of atoms for each element in a compound e.g CH₄ or C₂H₄

1. What is a ‘homologous series’?

 a family of hydrocarbons with similar chemical properties who share the same general formula

1. Give features that a homologous series of molecules share

They have the same general formula and they have the same chemical properties ; they share a trend in their physical properties, each additional member of the series differs by –CH₂ ; they share a functional group

1. What is combustion?

When a fuel (hydrocarbon) reacts with oxygen to produce carbon dioxide and water

1. What are the two products of complete combustion?

Carbon dioxide and water

1. What is a substitution reaction?

When an atom in a compound is replaced by another atoms e.g. When an alkane reacts with a halogen, a hydrogen is replaced by a halogen

1. Give the word and symbol equation for the reaction of methane and bromine

Methane + bromine-> Bromomethane + hydrogen bromide

CH₄ + Br₂ -> CH₃Br + HBr

1. What is needed for halogenation of an alkane to occur?

UV light

1. When an methane reacts with bromine (under UV light), what colour change is seen?

The mixture turns from orange to colourless

1. What is cracking?

The thermal decomposition of a long chain hydrocarbon into small chain molecules

1. What catalyst and temperature is needed for cracking?

Alumina and around 600-700 ^oC

1. Why do we crack long chain hydrocarbons?

We crack them because small chain hydrocarbons are more useful and we have a surplus (too much) long chain hydrocarbons from crude oil.

1. What is thermal decomposition?

When heat is used to break down a compound. There is always one reactant but many products (e.g. A → B + C)

1. What does saturated mean?

The hydrocarbon only contains single carbon bonds

1. What is the general formula for an alkene?

CnH2n

1. Why are Alkenes unsaturated?

They contain a double bond between two carbon atoms

1. How can you test is a substance is an alkane or an alkene?

Add bromine water to it. If it stays yellow - it is an alkane, if it turns colourless it is an alkENE

1.  What is incomplete combustion and why does it happen?

When a fuel burns in insufficient oxygen incomplete combustion can occur. Carbon monoxide can be produced which is toxic

1. Why is carbon monoxide toxic?

It stops the blood cells from transporting oxygen around our bodies efficiently

1. What is a polymer?

A long chain molecule made from monomers joined end to end

1. What is a monomer?

A small molecule that can be joined to another monomer to make a polymer