Chemical analysis

Question 1

what is a pure substance?

Answer 1

contains only one type of compound or element

Question 2

why is purity important?

Answer 2

only pure substances melt and boil and a specific temp

Question 3

what is a formulation?

Answer 3

a mixture that has been designed as a useful product.

Question 4

how are formulations made?

Answer 4

by mixing the components in carefully measured quantities to ensure that the product has required properties

Question 5

what are some examples of formulations?

Answer 5

fuels, cleaning agents, medicine, fertilisers and food and alloys

Question 6

if we test a substance for purity by measuring its boiling point, is that a physical test or a chemical test?

Answer 6

physical.

Question 7

what is the mobile phase?

Answer 7

where the molecules can move (solvent)

Question 8

what is the stationary phase?

Answer 8

molecules can’t move (paper)

Question 9

what will happen if none of the substances are soluble?

Answer 9

the ink won’t move

Question 10

what are the spots left behind in chromatography?

Answer 10

chromotogram.

Question 11

how do you calculate the rF value?

Answer 11

distance travelled by substance/ distance travelled by solvent.

Question 12

how do you spot a pure substance in chromatography?

Answer 12

it wont separate so there will only be one dot and only one rF value.

Question 13

what is chromatography used for?

Answer 13

to separate a mixture of soluble substances in liquids.

Question 14

what colour does a flame turn in the presence of calcium ions?

Answer 14

orange-red

Question 15

what colour does a flame turn in the presence of copper ions?

Answer 15

green

Question 16

what colour does a flame turn in the presence of lithium ions?

Answer 16

crimson

Question 17

what colour does a flame turn in the presence of potassium ions?

Answer 17

lilac

Question 18

what colour does a flame turn in the presence of sodium ions?

Answer 18

yellow

Question 19

how do you do a flame test?

Answer 19

light a bunsen burner and open air hole for blue flame. pick up small sample of solid salt on a clean loop wire. hold the sample in the edge of the flame. observe and record flame colour. wash loop with dilute hydrochloric acid before continuing with other flame tests.

Question 20

what is the method to test for metal cations?

Answer 20

dissolve a little solid salt in a test tube using distilled water. add a few drops of dilute NaOH solution drop wise. record any precipitate formed.

Question 21

what’s the method for testing for ammonium ions?

Answer 21

dissolve a little solid salt in a test tube using distilled water. add dilute NaOH solution and heat gently. remove the flame and hold a piece of damp red litmus paper near mouth of test tube. record any changes in colour.

Question 22

what is the method for testing for carbonate ions?

Answer 22

put little solid salt in a test tube and add a few drops of dilute acid. record of any bubbling occurs. use limewater to check that any bubbles contain limewater.

Question 23

what is the method for testing for aulfate ions?

Answer 23

dissolving a little solid salt in a test tube using distilled water. add a few drops of dilute hydrochloric acid, and then add a few drops of chloride solution. record if a white precipitate forms.

Question 24

what is the method for testing for halide ions?

Answer 24

dissolve a little solid salt in a test tube using distilled water. add a few drops of silver nitrate solution. record the colour of any precipitate formed.

Question 25

how do you identify metal ions (cations) in compounds?

Answer 25

flame test

Question 26

how do you test for cations?

Answer 26

using sodium hydroxide

Question 27

what is the result when aluminium ions are tested for?

Answer 27

a white precipitate that dissolved in excess sodium hydroxide.

Question 28

what is the result when calcium ions are tested for?

Answer 28

white precipitate

Question 29

what is the result when copper (II) ions are tested for?

Answer 29

blue precipitate