C12.1 - C12.6 - Chemical Analysis✔️

Question 1

What is a pure substance?

Answer 1

A substance that is made up of just one substance - that substance can either be an element or compound

Question 2

What are an elements fixed points?

Answer 2

The melting and boiling points of an element or a compound are called its fixed point

Question 3

How can fixed points be used to identify pure elements and compounds?

Answer 3

Pure elements and compounds melt and boil at specific temperatures and these fixed points can be used to identify them - meltinga point and boiling point data can be used to distinquish pure substances

Question 4

What are fomulations?

Answer 4

formulations are useful mixtures made up in definite proportions,designed to give a product the best properties possible to carry out its function

Question 5

Why is chromatography used?

Answer 5

Used to seperate mixtures and give information to help identify substances - involves a stationary phase and a mobile phase - seperation depends on the distribution of susbstances between the phases

Question 6

What are Rբ values?

Answer 6

Retention factor value which can be measured and matched against databases to identify substances

Question 7

Equation for Rբ?

Answer 7

Rբ = distance moved by a substance / distance moved by solvent

Question 8

What will happen to the compounds in a mixture when they seperate?

Answer 8

Compounds will seperate into different spots depending on the solvent - but pure compounds will produce a single spot in all solvents

Question 9

What is the test for hydrogen?

Answer 9

Use a burning splint held at the open end of a test tube of the gas - hydrogen burns rapidly with a pop sound

Question 10

What is the test for oxygen?

Answer 10

Uses a glowing splint inserted into a test tube of the gas - splint relights in oxygen

Question 11

What is the test for chemical dioxide?

Answer 11

Uses an aqueous solution or calcium hydroxide (lime water) when carbon dioxide is shaken with or bubbled through limewater the limewater turns milky (cloudy)

Question 12

What is the test for chlorine?

Answer 12

Uses litmus paper - which when damp blue litmus paper is put into chlorine the litmus paper is bleached and turns white

Question 13

Colour for the lithium ion(Li+) in a flame test?

Answer 13

Crimson

Question 14

Colour for sodium ion (Na+) in a flame test?

Answer 14

Yellow

Question 15

Colour for potassium ion (K+) in a flame test?

Answer 15

Lilac

Question 16

Colour for clacium ion (Ca2+) in a flame test?

Answer 16

Orange- red

Question 17

Colour for copper ion (Cu2+) in a flame test?

Answer 17

Green

Question 18

Explain how a flame test is set up?

Answer 18

• nichrom wire loop dipped in concentrated hydrochloric aicd and heated (to clean it)
• dipped in acid again before being dipped into metal compound being tested
• hold loap in roaring flame of bunsern burner
• use colour of flame to identify metal ion in the compound

Question 19

Why is sodium hydroxide solution used?

Answer 19

Can be used to identify metal ions that form insoluble hydroxides in precipitation reactions

Question 20

What ions form white precipitates when tested with sodium hydroxide solution?

Answer 20

• aluminium ions
• calcium ions
• magensium ions

Question 21

What happens if you add more sodium hydroxide to aluminium ions,calcium ions and magensium ions?

Answer 21

The precipitate formed with aluminium ions dissolves however the white precipitate formed with calcium or magnesium ions will not dissolve (so calcium and magnesium can be distinguished by a flame test)

Question 22

What colour precipitates forms with copper(II) ions?

Answer 22

Blue precipitate

Question 23

What colour precipitates forms with iron(II) ions?

Answer 23

Green precipitate is produced

Question 24

What colour precipitates forms with iron(III) ions?

Answer 24

Brown precipitate is formed

Question 25

How can you test a substance for being a carbonate?

Answer 25

Add dilute acid to a carbonate - it fizzes and produces carbon dioxide gas - the gas turns limewater milky (cloudy)

Question 26

What happens with carbon dioxide gas in limewater - explain why this happens?

Answer 26

Carbon dioxide reacts with the alkaline, calcium hydroxide - it forms a white precipitate of calcium carbonate which turns the limewater milky (cloudy)

Question 27

How can you identify halides?

Answer 27

By adding dilute nitric acid and then silver nitrate solution which produces a precipitate of silver halide

Question 28

Which colour will the precipitates be when identifying halides?

Answer 28

• Chloride - white
• bromide - cream
• iodide - yellow

Question 29

How can you test for sulfates?

Answer 29

By adding hydrochloric acid (to remove carbonate ions that would form)and then barium chloride solution which produces a white precipitate of barium sulfate (which tells you sulfate ions are present)

Question 30

Benefits of modern instrumental methods over older?

Answer 30

• they are highly accurate and sensitive
• they are quicker
• they enable small samples ro be analysed

Question 31

Disadvantages of using instrumental methods are that the equipment …?

Answer 31

• is usually expensive
• takes special training to use
• gives results that can often be interptreted only by comparison with data from known substances

Question 32

What is flame emission spectroscopy?

Answer 32

An exmaple of an instrumental method which will tell us which metal ions are present from their characteristics line spectra and also the concentration of metal ions in a solution

Question 33

How are fomulations made?

Answer 33

Made by mixing the components in carefully measured quantities to ensure that the product has the required properties - examples formulations are fuels,medicines and foods

Question 34

How can Rբ values be used to identify compounds?

Answer 34

Different compounds have different Rբ values in different solvents, which can be used to help identify the compounds

Question 35

How can chromatography be used to seperate mixtures of substances dissolved in a solvent?

Answer 35

Mixture of substances dissolved in a solvent move up a piece of chromatography paper - the different substances are seperated because of their different solubilities in the solvent used