Pure And Impure Substances

Question 1

Molecules

Answer 1

2 or more atoms held together by chemical bonds

Question 2

Alloy

Answer 2

A mixture of a metal with one of more elements

Question 3

Pure substances

Answer 3

Natural substances that haven’t been processed or changed

Question 4

How do you use melting points to determine purity?

Answer 4

The melting point of a pure substance is a single temperature

Question 5

Chromatography

Answer 5

Used to separate mixtures of soluble substances in liquids

Question 6

Chromatography relies on 2 different phases:

Answer 6

A stationary phase that does NOT move (solvent)
A mobile phase that DOES move (solute)

Question 7

Step by step method on how to set up paper chromatography

Answer 7

1. Draw a pencil line across the chromatography paper around 1-2 cm from the bottom
2. Use a pipette or capillary tube to add small spots of each ink to the line on the paper
3. Place the paper into a container with a suitable solvent in the bottom
4. Allow the solvent to move through the paper but remove the chromatography before it reaches to the top
5. Allow the chromatography to dry and then measure the distances travelled by each spot and by the solvent

Question 8

Advantages and disadvantages of TLC

Answer 8

Advantages:
1. Easy method to separate components
2. Less equipment used
3. Non-volatile compounds can be separated by this method
Disadvantages:
1. Results are hard to reproduce
2. Not an automatic process
3. Qualitative not quantitative analysis
4. Applicable for soluble mixture components only

Question 9

Advantages and disadvantages of paper chromatography

Answer 9

Advantages:
1. Small amounts of sample mixture
2. An easy method of separation of components
3. Relatively cheap
Disadvantages:
1. Cannot handle large amounts of sample mixture
2. Ineffective in quantitative analysis.
3. Not as accurate as gas chromatography

Question 10

Advantages and adisadvantages of gas chromatography

Answer 10

Advantages:
1. Very accurate and precise
2. Fast separation and small sample requirement
Disadvantages:
1. Not suitable for large samples
2. Compounds need to be volatile
3. High sensitivity

Question 11

Rf value

Answer 11

Distance of component (substance) / distance of solvent (liquid)