Topic 8 - Chemical Analysis

Question 1

What is a pure substance

Answer 1

Something that contains only one compound or element

Question 2

What will impurities do to the melting and boiling point of a substance

Answer 2

Lower the melting point and increase the boiling point

Question 3

What will impurities do the melting and boiling ranges of a subatance

Answer 3

It will increase

Question 4

How can you find whether a substance is pure

Answer 4

Measure its melting and boiling point and compare it to that of the pure substance

Question 5

What’s a formulation

Answer 5

Mixtures made for a specific purpose by following a formula e.g cleaning products

Question 6

What’s the mobile phase of paper chromotography

Answer 6

The solvent

Question 7

Whats the stationary phase of paper chromatography

Answer 7

The paper

Question 8

In paper chromatography, what does how far a chemical move depend on

Answer 8

Whether it spends more time in the mobile or stationary phase. If it spends more time in the mobile phase it will move more.

Question 9

What does how much time the molecules spend in each phase depend on

Answer 9

How soluble they are in the solvent and how attracted they are to the paper

Question 10

What’s the formula for Rf value

Answer 10

Distance travelled by substance (B) ÷ distance travelled by the solvent (A)

Question 11

How do you find out if a certain substance is in a mixture using paper chromotography

Answer 11

1) run a pure sample of that substance alongside the unknown mixture
2) do this multiple times in different solvents
3) measure Rf values
4) if the Rf value of the pure substance matches one of the Rf values of one of the spots in the mixture in all of the solvents it’s likely the substance is present

Question 12

What’s the test for chlorine

Answer 12

Use damp litmus paper - chlorine will turn the paper from blue to white

Question 13

What’s the test for oxygen

Answer 13

A glowing splint - oxygen will cause it to relight

Question 14

What’s the test for carbon dioxide

Answer 14

Bubbling through limewater (calcium hydroxide) - carbon dioxide will turn it cloudy

Question 15

What’s the test for hydrogen

Answer 15

Lit splint- hydrogen will make a sqeaky pop

Question 16

What’s a catbonate

Answer 16

A substance that contains CO3 2- ions

Question 17

What’s the test for carbonates

Answer 17

Put a sample of the solution in a test tube and then use a dropping pipette to add a couple drops of dilute acid. Then connect the test tube to a test tube filled with limewater. If carbonates are present, carbon dioxide will be released, causing the limewater to go cloudy

Question 18

What’s the formula for a sulfate ion

Answer 18

SO4 2-

Question 19

What’s the test for sulfates

Answer 19

Use a dropping pipette to add a couple drops of dilute hydrochloric acid, followed by a couple drops of barium chloride solution to test tube containing th solution - if sulfate ions are present white precipitate will form

Question 20

What is the test for halides

Answer 20

Add a couple drops of dilute nitric acid (HNO3), followed by a couple drops of a silver nitrate solution (AgNO3) to the solution

Question 21

What are the results of the halide test

Answer 21

Chloride = white precipitate of silver chloride
Bromide = cream precipitate of silver bromide
Iodide = yellow precipitate of silver iodide

Question 22

What’s the method for flame tests

Answer 22

1) clean a platinum loop by dipping it into some dilute HCl and then holding it in a blue flame until it burns w/o any colour
2) dip the clean loop into the sample and place it back into the flame

Question 23

What’s the results of the flame test

Answer 23

Lithium ions = crimson flame
Sodium ions = yellow flame
Potassium ions = lilac flame
Calcium ions = orange - red flame
Copper ions = green flame

Question 24

What the method for the precipitate test

Answer 24

Add a few drops of sodium hydroxide solution to the mystery compound. If you get a coloured insoluble hydroxide you can often tell what metal is in the compound.

Question 25

What’s the results of the precipitate test

Answer 25

Calcium = white precipitate
Magnesium = white precipitate
Aluminium = white precipitate (re dissolves when excess NaOh)
Copper = blue precipitate
Iron II = green precipitate
Iron III = brown precipitate

Question 26

What can a flame emission spectroscopy test be used for

Answer 26

To identify ions in solutions + calculate concentrations. It can also be used to identify different ions in mixtures making it more useful than flame tests

Question 27

Why does each ion have a unique light spectrum

Answer 27

Combinations of wavelength emitted by an ion depends on its charge and its electron arrangement

Question 28

What’s the advantages of instrumental analysis

Answer 28

• very sensitive
• very fast
• very accurate