C12 - Chemical Analysis

Question 1

What is a pure substance?

Answer 1

A substance made up of only one specific substance, whether it be element or compound.

Question 2

How are substances tested for purity?

Answer 2

The melting and boiling points of a substance are fixed, so this can be used to test a substance’s purity. Generally, impurities lower melting point and raise boiling point of a substance.

Question 3

What is a formulation?

Answer 3

A mixture that has been designed to produce a useful product for a specific use, e.g. medication.

Question 4

How are chromatogram results presented?

Answer 4

As a Rf value - retention factor. Worked out using Rf = distance moved by substance / distance moved by solvent.

Question 5

How are Rf values used?

Answer 5

Rf values are stored in databases, so unknown chemicals found in other chromatograms can be compared to a database to ID the chemical.

Question 6

How are gases collected for testing?

Answer 6

Boiling tube placed over test tube, then turned over to perform test.

Question 7

How is hydrogen tested for?

Answer 7

Lit splint held at end of test tube - splint “pops”.

Question 8

How is oxygen tested for?

Answer 8

Glowing splint held in test tube - splint relights.

Question 9

How is carbon dioxide tested for?

Answer 9

Bubble gas through limewater (calcium hydroxide solution) using a test tube with a glass straw - limewater turns cloudy.

Question 10

How is chlorine tested for?

Answer 10

Dampened blue litmus paper held at end of test tube - turns white, gets bleached.

Question 11

What are the results for flame tests with lithium?

Answer 11

Crimson.

Question 12

What are the results for flame tests with sodium?

Answer 12

Yellow.

Question 13

What are the results for flame tests potassium?

Answer 13

Lilac.

Question 14

What are the results for flame tests with calcium?

Answer 14

Orange-red.

Question 15

What are the results for flame tests with copper?

Answer 15

Green.

Question 16

What materials can be tested for with sodium hydroxide?

Answer 16

Copper2+, Iron2+, Iron3+, Aluminium3+, Mg2+, Ca2+.

Question 17

What is the testing process with sodium hydroxide?

Answer 17

https://cdn.discordapp.com/attachments/303250641575215115/414766076845359105/unknown.png

Question 18

How are carbonates tested for?

Answer 18

Adding a dilute acid to a carbonate, then bubbling the gas produced through limewater - limewater turns cloudy if positive.

Question 19

How are halides (chlorides, bromides, iodides) tested for?

Answer 19

Adding nitric acid, then silver nitrate solution. If solution is yellow, iodide is positive. If solution is cream, bromide is positive. If solution is white, chloride is positive.

Question 20

How are sulfates tested for?

Answer 20

Adding hydrochloric acid, then barium chloride solution. If solution turns white, sulfate is positive.

Question 21

What is instrumental analysis?

Answer 21

Instrumental analysis is using special machines and technology to test materials, instead of a practical experiment.

Question 22

What are the advantages and disadvantages of instrumental analysis?

Answer 22

+ Highly accurate.
+ Quick.
+ Allow very small samples to be analysed.

• Very expensive.
• Requires special training.
• Gives data that can only be compared with other known substances.

Question 23

What is flame emission spectroscopy?

Answer 23

Heating a sample in a flame, then shining the light produced against a white sheet, then using the spectogram shown to identify the components of the sample. It can also show the concentration of the metal ions in a solution.