chemical analysis

Question 1

what is the test for hydrogen?

Answer 1

a pop sound when a lighted splint is in a at the end of test tube containing hydrogen gas

Question 2

what is the test for oxygen?

Answer 2

a glowing splint relights in a test tube of oxygen

Question 3

what is the test for carbon dioxide?

Answer 3

lime water ( calcium hydroxide ) turns cloudy when co2 is present

Question 4

what is the test for chlorine?

Answer 4

litmus paper is bleached or turns white

Question 5

what is the test for water?

Answer 5

copper sulphate turns blue

Question 6

what is a pure substance?

Answer 6

a single element or compound not mixed with any other substance

Question 7

how can boiling/melting points be used to determine the impurity of a substance?

Answer 7

the higher the boiling point ( from the pure element/compound) the impurer the substance - vicea versa for melting point

Question 8

how do you identify positive ions in a solid ionic compound?

Answer 8

the flame test: dip wire loop into conc hcl and then into solid compound and then place in Bunsen flame

Question 9

how do you identify positive ions in a solution of an ionic compound?

Answer 9

add naoh

sodium hydroxide

Question 10

how do you identify halide ions in a solution of an ionic compound?

Answer 10

add dilute nitric acid then the silver nitrate

Question 11

what colour is the flame in a flame test when sodium is present?

Answer 11

yellow

Question 12

what colour is the flame in a flame test when potassium is present?

Answer 12

lilac

Question 13

what colour is the flame in a flame test when calcium is present?

Answer 13

orange/red

Question 14

what colour is the flame in a flame test when barium is present?

Answer 14

green

Question 15

what is the result when chloride is present ( in a test for negative ions )?

Answer 15

white precipitate

Question 16

what is the result when chloride is present ( in a test for negative ions )?

Answer 16

white precipitate

Question 17

what is the result when bromide is present ( in a test for negative ions )?

Answer 17

cream precipitate

Question 18

what is the result when iodide is present ( in a test for negative ions )?

Answer 18

yellow precipitate

Question 19

what is the test for sulphate and what is the positive result?

Answer 19

white precipitate

add dilute hcl and then barium chloride

Question 20

how do you differentiate between aluminium, calcium and magnesium?

Answer 20

add excess naoh and then only aluminium will form a colourless solution
then use a flame test to differentiate between calcium and magnesium

Question 21

what is the positive result for a test for an ionic solution containing aluminium?

Answer 21

white precipitate

Question 22

what is the positive result for a test for an ionic solution containing calcium?

Answer 22

white precipitate

Question 23

what is the positive result for a test for an ionic solution containing magnesium?

Answer 23

white precipitate

Question 24

what is the positive result for a test for an ionic solution containing copper?

Answer 24

blue precipitate

Question 25

what is the positive result for a test for an ionic solution containing iron (II)?

Answer 25

green precipitate

Question 26

what is the positive result for a test for an ionic solution containing iron (III)?

Answer 26

brown precipitate

Question 27

what is precipitate?

Answer 27

Precipitation is the process of conversion of a chemical substance into a solid from a solution by converting the substance into an insoluble form or a super-saturated solution. When the reaction occurs in a liquid solution, the solid formed is called the precipitate

Question 28

what are two advantages of of instrumental methods compared with chemical tests for identifying chemicals?

Answer 28

less time | less chemicals used

Question 29

why is it difficult to identify the metal ions from the colour of the flame, if there are various ions in the compound?

Answer 29

because the colours are masked / can only see one colour

Question 30

how would you test for the presence of sulphate ions and what would the positive result be?

Answer 30

add barium chloride (solution) add hydrochloric acid white precipitate produced

Question 31

how do you test a solution to see if carbonate ions are present?

Answer 31

add dilute acid | limewater (turns) cloudy / milky

Question 32

what is the retention factor?

Answer 32

distance travelled by substance / distance travelled by solvent ( solvent front )

Question 33

why must the line be in pencil in chromatography?

Answer 33

because pencils are insoluble