chemical analysis (required practicals)

Question 1

what is a pure substance?

Answer 1

a substance that only contains 1 compound or element.

Question 2

how can you test the purity of a substance using boiling or melting points?

Answer 2

1. a pure substance will melt or boil at a specific temperature.
2. you can measure a substances melting or boiling point and compare it against the pure substance.
3. the closer your melting point is to the actual substance the more pure it is.
4. impurities lower the melting point and increase the boiling point.

Question 3

what is a formulation?

Answer 3

mixtures with a specific purpose that are made by following a formula. each component is in a measured quantity

Question 4

how does chromatography work? not how to do it

Answer 4

1. during chromatography the substances in the sample move between the mobile and stationary phase. an equilibrium is formed between the phases
2. the mobile phase moves through the stationary phase and anything dissolved whilst in the mobile phase moves with it. how quickly a chemical moves depends on what phase it spends more time in
3. the chemicals that spend more time in the mobile phase than in the stationary phase will move further.

Question 5

what effects the amount of time a substance spends in the mobile and stationary phase?

Answer 5

how soluble the substance is in the solvent.
how attracted they are to the paper.
during paper chromatography the stationary phase is the paper and the mobile phase is the solvent.

Question 6

what is an Rᶠ value?

Answer 6

a ratio between how far a substance has travelled compared to the solvent.

Question 7

what is the formula for calculating the Rᶠ value? (practical apparently)

Answer 7

Rᶠ = distance travelled by substance ÷ distance travelled by solvent

Question 8

how do you test for chlorine gas? (practical)

Answer 8

chlorine bleaches damp litmus paper.

Question 9

how do you test for oxygen? (practical)

Answer 9

a glowing splint will relight in a test tube containing oxygen.

Question 10

how do you test for carbon dioxide? (practical)

Answer 10

carbon dioxide turns a solution of calcium hydroxide cloudy.

Question 11

how do you test for hydrogen? (practical)

Answer 11

a lit splint causes a squeaky pop at the end of a test tube containing hydrogen.

Question 12

how do you test for carbonates using dilute acid? (practical)

Answer 12

add a few drops of dilute acid to a sample.
connect a test tube of this to another with limewater.
carbon dioxide turns limewater cloudy.
(carbonates release carbon dioxide)

Question 13

how do you test for sulfates using hcl and barium chloride? (practical)

Answer 13

add a few drops of dilute hcl and a few drops of barium chloride to a sample.
if sulfate ions are present a white precipitate will form.

Question 14

how do you test for halides using nitric acid and silver nitrate? (practical)

Answer 14

add a few drops of dilute nitric acid and a few drops of silver nitrate solution to a sample.
a chloride forms a white precipitate.
a bromide forms a cream precipitate.
an iodide forms a yellow precipitate.

Question 15

how do you identify metal ions with flame tests? (practical)

Answer 15

clean a metal loop by holding it in a blue flame until it turns yellow.
dip the loop into a sample and hold it over the flame to see the colour.
lithium ions - crimson.
sodium ions - yellow.
potassium ions - lilac.
calcium ions - orange.
copper ions - green.