Chemical Analysis

Question 1

What is a pure substance?

Answer 1

A pure substance may consist of a single element or compound which contains no other substances.

Question 2

What is an example of a pure substance?

Answer 2

A beaker of a sample of pure water contains only H2O molecules and nothing else.

Question 3

What is a mixture?

Answer 3

A mixture consists of two or more elements or compounds that are physically mixed together, they are not chemically combined.

Question 4

What happens to the chemical properties of a substance in a mixture?

Answer 4

Remains unchanged.

Question 5

How can substances in mixtures be separated?

Answer 5

Substances in mixtures can be separated by physical means.

Question 6

What happens to pure substances when they melt and boil?

Answer 6

They melt and boil at specific and sharp temperatures e.g. pure water has a boiling point of 100 degrees and a melting point of 0 degrees.

Question 7

What are the boiling and melting points of mixtures?

Answer 7

Mixtures have a range of melting and boiling points as they consist of different substances that tend to lower the melting point and broaden the melting point range.

Question 8

What can melting and boiling points be used for?

Answer 8

They can be used to distinguish pure substances from mixtures.

Question 9

What is a formulation?

Answer 9

A formulation is a mixture that has been designed for a specific purpose to deliver a commercial product.

Question 10

How are formulations and complex mixtures made?

Answer 10

Formulations are complex mixtures that are made by following an exact recipe.

Question 11

What is an example of an everyday formulation?

Answer 11

Paint.

Question 12

What does paint contain?

Answer 12

Pigment: gives the paint colour.
Binder: forms a film that holds the pigment in place.
Solvent: used to dissolve the other components and alter the viscosity.

Question 13

What are formulations important in?

Answer 13

Formulations are very important in the pharmaceutical industry where the exact ratios of each component must be precise.

Question 14

How can changing the formulations of particular medicine do something?

Answer 14

By changing the formulation of a particular medicine chemists can make sure it delivers the drug to the correct part of the body at the right concentration, that it’s safe to consume and has an adequately long shelf life.

Question 15

What are examples of formulations?

Answer 15

Fuels, cleaning agents, alloys, fertilisers and foods.

Question 16

What is chromatography used for?

Answer 16

Chromatography is used to separate substances and provide information to help identify them.

Question 17

What do the components of chromatography have?

Answer 17

The components have different solubilities in a given solvent (e.g. different coloured inks that have been mixed to make black ink) and different adhesion to the supporting medium - usually paper.

Question 18

What is the equation to determine the Rf value?

Answer 18

Rf = Distance moved by substance/distance moved by solvent.

Question 19

What does the test for hydrogen consists of?

Answer 19

Holding a burning splint held at the open end of a test tube of gas.

Question 20

If hydrogen is present wants happens in the tube of gas?

Answer 20

If the gas is hydrogen it burns with a loud “squeaky pop” which is the result of the rapid combustion of hydrogen with oxygen to produce water.

Question 21

What should you not do in the test for Hydrogen?

Answer 21

Be sure not to insert the splint right into the tube, just at the mouth, as the gas needs air to burn.

Question 22

What is the test for Oxygen?

Answer 22

• The test for oxygen consists of placing a glowing splint inside a test tube of gas.
• If the gas is oxygen the splint will relight.

Question 23

What is the test for carbon dioxide?

Answer 23

• The test for carbon dioxide involves bubbling the gas through an aqueous solution of calcium hydroxide (limewater).
• If the gas is carbon dioxide, the limewater turns milky or cloudy.

Question 24

What is the test for Chlorine?

Answer 24

• The test for chlorine makes use of litmus paper.
• If chlorine gas is present, damp blue litmus paper will be bleached white.
• It may turn red briefly before bleaching, as acids are produced when chlorine comes into contact with water.
• Chlorine should always be handled in a fume cupboard due to its toxicity.