Chemical analysis

Question 1

What is purity in chemistry?

Answer 1

Something that only contains one element or compound

Question 2

How can the boiling/melting point of a substance tell you how pure it is?

Answer 2

All pure substances melt or boil at a specific temperature so the closer the value measured is to the boiling/melting point it is purer.

Question 3

What will impurities do to your substance?

Answer 3

It will lower the melting point and increase the boiling point whilst also increasing the range of temperatures.

Question 4

What is a formulation?

Answer 4

A formulation is a mixture made in a specific way for a specific purpose and recipe.

Question 5

What can formulations be used for?

Answer 5

In the pharmaceutical industry for pills, paint, fuels, cleaning products.

Question 6

What is paper chromatography

Answer 6

It is an analytical method to separate the substances in a mixture.

Question 7

What is the mobile phase?

Answer 7

Where the molecules can move - this is a liquid or a gas.

Question 8

What is the stationary phase?

Answer 8

Where the molecules cannot move- this is a solid or a thick liquid.

Question 9

What do substances do between the phases and how does this affect how long a molecule moves?

Answer 9

Substances move between the two phases and an equilibrium is formed. How far a molecule moves depends on how long it spends in the mobile phase.

Question 10

Why do some molecules spend in longer in a certain phase?

Answer 10

How soluble they are in the solvent and how attracted they are to the paper. If they have a high solubility and are less attracted to the paper they will be in the mobile phase for longer.

Question 11

How can we analyze what is in a mixture in paper chromatography?

Answer 11

The different spots of chemicals will separate and we will see them distributed out.

Question 12

What is the Rf value?

Answer 12

It is the ratio between the dissolved substance and the distance travelled by the solvent front.

Question 13

How do you calculate the Rf value?

Answer 13

distance travelled by substance/ distance travelled by solvent.

Question 14

How do you test for chlorine?

Answer 14

Chlorine bleaches litmus paper but it may turn red for a second.

Question 15

How do you test for oxygen?

Answer 15

Place a glowing splint into a test tube and it will relight if oxygen is present.

Question 16

How do you test for hydrogen?

Answer 16

Place lit splint and there will be a squeaky pop if hydrogen is present.

Question 17

How do you test for carbon dioxide?

Answer 17

Bubble carbon dioxide through limewater and if it is present it will turn cloudy.

Question 18

How do you test for carbonates?

Answer 18

Add a couple of drops of dilute acid and then connect it to a tube of limewater. If carbonates are present it will turn cloudy.

Question 19

How do you test for sulfates?

Answer 19

Add a few drops of dilute hydrochloric acid and barium chloride to the test tube. If there are sulfate ions present a white precipitate will form.

Question 20

How do you carry out flame tests?

Answer 20

Clean a platinum loop with HCL and hold it to a blue bunsen burner until it burns without color. Next, dip the loop into the sample and record the colour of the flame

Question 21

What color flame will lithium ions produce?

Answer 21

Crimson

Question 22

What color flame will sodium ions produce?

Answer 22

Yellow

Question 23

What color flame will potassium ions produce?

Answer 23

Lilac

Question 24

What color flame will calcium ions produce?

Answer 24

Orange-red

Question 25

What color flame will copper ions produce?

Answer 25

Green

Question 26

How do you test for metals?

Answer 26

Metal hydroxides are insoluble and precipitate out of solution. These have certain colors. So add drops of sodium hydroxide solution to the metal.

Question 27

What is the color of the precipitate for calcium?

Answer 27

White

Question 28

What is the color of the precipitate for copper?

Answer 28

Blue

Question 29

What is the color of the precipitate for iron (II)?

Answer 29

Green

Question 30

What is the color of the precipitate for iron (III)

Answer 30

Brown

Question 31

What is the color of the precipitate for aluminium?

Answer 31

White at first but redissolves in excess NaOH to form a colorless solution.

Question 32

What is the color of the precipitate for magnesium?

Answer 32

White

Question 33

How do you test for halides?

Answer 33

Add some dilute drops of dilute nitric acid and some silver nitrate solution.

Question 34

What does chloride give as a precipitate?

Answer 34

A white precipitate and silver chloride.

Question 35

What does bromide give as a precipitate?

Answer 35

A cream precipitate and silver bromide

Question 36

What does iodide give as a precipitate?

Answer 36

A yellow precipitate and silver iodide.

Question 37

What is flame emission spectroscopy?

Answer 37

A sample is placed in a flame. As the ions heat up the electrons get excited and drop back to their original energy levels and at this point, they transfer energy through light. The light goes through a spectroscope which detects different wavelengths of light to produce a line spectrum,

Question 38

Why is there a different combination of wavelengths?

Answer 38

This depends on the charge and electron arrangement so they will emit different wavelengths of light.

Question 39

What does the intensity of the light indicate?

Answer 39

The concentration of the ion.

Question 40

Why is flame emission spectroscopy better than flame tests?

Answer 40

They can be used for mixtures, not just a single ion.

Question 41

What are the advantages of flame emission spectroscopy?

Answer 41

Accurate, fast, and sensitive.