C2.3 Covalent Compounds and Separation Techniques

Question 1

What is a Covalent Bond?

Answer 1

A pair of electrons shared between two atoms

Question 2

What does Covalent Bonding result in?

Answer 2

The formation of molecules

Question 3

Describe the properties of simple molecular covalent compounds

Answer 3

Have low melting and boiling point because there are only weak forces between molecules

Atoms in Small Molecular Covalent haven’t lost or gained electrons so there are no charged particles that can move around
This means that the substance is a poor conductor of electricity

Question 4

Describe the properties of giant molecular covalent substances

Answer 4

Have high melting and boiling points because of the strong covalent bond between atoms

Question 5

Explain why Graphite are used to make electrodes and as a lubricant whereas diamond is used in making cutting tools

Answer 5

Graphite is used to make electrodes because it conducts electricity from each carbon atom that can move along layers
Graphite is used as a lubricant because it easily rubs away in layers since there are only weak forces between the layers

Diamond is used to make cutting tools because it’s a hard material and all the atoms are joined with strong covalent bonds

Question 6

Describe the separation of two immiscible liquids using a separating funnel

Answer 6

1. The tap is opened so the lower liquid runs out of the funnel and can be collected in a beaker
2. Tap is then closed before the other liquid starts to run out
3. Put another beaker under the funnel, then open the tap to allow the upper liquid to be collected

Question 7

Describe the separation of mixtures of miscible liquids by Fractional Distillation

Answer 7

1. The mixture of liquids is heated and the liquids evaporate
2. The vapour condenses in a fractionating column
3. The fraction with the highest boiling point condenses near the bottom of the column where liquid oxygen is piped out
4. The fraction with the lowest boiling point reaches the top of the column where nitrogen gas is collected

Question 8

Describe how paper Chromatography can be used to separate and identify components of mixtures

Answer 8

A use of Chromatography is to separate out mixture of colouring agents in food. To identify, run samples of known mixtures alongside unknown and compare where spots end

1. Put spots of each mixture being tested on a pencil baseline on filter paper
2. Roll up the paper and put into beaker containing a solvent. Baseline must be kept above the level of solvent
3. Solvent seeps up the paper, taking sample with it
4. Different chemicals in sample form separate spots on paper
5. Results of Chromatography analysis is called a Chromatogram. The amount of spots means there is at least that number of substances in the mixture

Question 9

Evaluate the information provided by paper chromatograms, including the calculation of Rf values in a variety of contexts

Answer 9

Rf = Distance moved by compound/Distance moved by solvent

This is used in the food industry and forensic science and scientists keep tables of these values and refer to them to identify substances like food additives and drugs