Chapter 8: Chemical Analysis

Question 1

What is different about the boiling points of mixtures?

Answer 1

They boil over a range of temperatures

Question 2

How does grit work?

Answer 2

Mixes with rain water and makes it so it melts below 0 degrees

Question 3

How does antifreeze work?

Answer 3

You mix it with water to lower the freezing point

Question 4

What is a formulation?

Answer 4

A mixture that has been designed as a useful product

Question 5

Name some examples of formulations

Answer 5

Alloys (mixtures of metals with other elements to make them stronger), Fuels (mixtures of hydrocarbons), Fertilisers (PO, KO), medicines, cleaning agents, foods, paints (contain binders)

Question 6

What is chromatography?

Answer 6

A technique that can be used to separate mixtures

Question 7

Describe the process of paper chromatography

Answer 7

1. A pencil line is drawn near the bottom of the chromatography paper (pencil does not dissolve in solvent)
2. Small amounts of the substances being analysed are placed in spots on the pencil line
3. The paper is hung in a beaker of the solvent (the pencil line must be above the solvent level)
4. The solvent soaks up the paper
5. When the solvent is near the top, the paper is removed from the solvent and the level the solvent reached (solvent front) is measured

Question 8

How do you tell if a substance is pure using chromatography?

Answer 8

It only produces one spot. Mixtures will produce a spot for each substance, however sometimes both spots travel the same distance

Question 9

How does chromatography work?

Answer 9

Substances with a stronger attraction to the solvent move quickly and travel a long way up the paper. Substances with a stronger attraction to the paper move slowly and only travel a short distance

Question 10

What is the Rf value?

Answer 10

The ratio of the distance moved by a substance to the distance moved by the solvent

Question 11

Name the test for oxygen

Answer 11

Insert a glowing splint into the gas and see if it relights

Question 12

Name the test for hydrogen

Answer 12

Insert a lit splint into the gas and listen for a squeaky pop sound

Question 13

Name the test for carbon dioxide

Answer 13

The gas is bubbled through limewater, which goes cloudy

Question 14

Name the test for chlorine

Answer 14

Insert red or blue litmus paper into the gas and see if it loses its colour

Question 15

How do you do a flame test?

Answer 15

Dip a damp splint into the compound and place it into a roaring Bunsen flame

Question 16

Name the colours produced by different cations

Answer 16

Lithium = Crimson red, Sodium = Orange/yellow, Potassium = Lilac, Calcium = Red/orange, Copper = green

Question 17

Why might it be hard to identify the cations in a mixture?

Answer 17

The different cations could produce different colours which could mix together

Question 18

What is a precipitate?

Answer 18

A solid formed when multiple solutions are mixed

Question 19

How would you use sodium hydroxide to identify cations?

Answer 19

Add sodium hydroxide solution to a solution of the substance being analysed, and some ions will produce a precipitate