Chemical tests

Question 1

What is tollens reagent use to test for

Answer 1

aldehydes

Question 2

What is bromine water used to test for

Answer 2

alkenes ( Electrophilic addition occurs)

Question 3

how do you carry out a flame test

Answer 3

dip a nicrome wire in hydrochloric acid then dip it in the unknown compound and hold it over a bunson burner

Question 4

which silver halides dissolve in concentrated ammonia

Answer 4

silver chloride and silver iodide

Question 5

write an equation for the white precipitate formed when using barium ions to test for sulfide ions

Answer 5

Ba^2+(aq) + SO4^2+(aq) =) BaSO4(s)

Question 6

what colour change will indicate a positive result when using bromine water to test for alkenes

Answer 6

the solution should go from orange to colourless

Question 7

What conditions are needed when using fehilings solution to test for aldehydes

Answer 7

you need to heat the solution

Question 8

what can be used to test for carboxylic acids

Answer 8

Solid sodium carbonate

Question 9

How do you test for carbonate ions

Answer 9

you add dilute hydrochloric acid ( or any acid)

Question 10

what factor of hydroxide ions is their chemical test bassed on

Answer 10

the fact that they make solutions alkaline

Question 11

if ammonia is present what colourchange wil be observed on the damp red litmous paper

Answer 11

the paper will turn from red to blue

Question 12

which silver hialides dissolve in dilute ammonia

Answer 12

silver chloride

Question 13

what colour precipitate does bromide give when testing for halide ions

Answer 13

A cream precipitate ( of silver bromide)

Question 14

what is solid sodium carbonate used to test for

Answer 14

carboxylic acids

Question 15

write an equation for how the silver mirror is formed when tollens reagent is mixed with an aldehyde to form a silver mirror

Answer 15

Ag+(aq) + e- =) Ag(s)

Question 16

What does a solution turning from orange to green in acidified potassium dichromate indicate

Answer 16

a primary and/or secondary alcohol is present

Question 17

what is it important to do when using bromine water to test for alkenes

Answer 17

shake the test tube

Question 18

what colour change will indicate a positive resut for fehlings solution

Answer 18

a blue solution to a brick red precipitate

Question 19

when tollings solution is mixed with an aldehyde what colour change is observed

Answer 19

the solution will go from colourless to form a silver mirror

Question 20

write an equation to show how potassium dichromate is oxidised when mixed with a primary or secondary alcohol

Answer 20

Cr2O7 + 6e- =) 2Cr^3+ + 7H2O

Question 21

in a flame test what colour does barium (Ba^2+) burn

Answer 21

pale green

Question 22

What reagent is used to test for primary and secondary alcohols. (HINT: it acts as a reducing agent)

Answer 22

Potassium dichromate (VI)

Question 23

in a flame test what colour does calcium (Cu^2+) burn

Answer 23

brick red

Question 24

how can you test for ammonium ions

Answer 24

using damp red litmous paper

Question 25

how do you test for sulfide ions

Answer 25

you add dilute hydrochloric acid followed by barium chloride solution

Question 26

how do you test for hydroxide ions

Answer 26

using a PH indicatior for example using red litmous paper if the ions are present the paper will go from red to blue

Question 27

What colour precipitate des iodide give when testing for halide ions

Answer 27

a yellow precipitate (of silver iodide)

Question 28

what do you need to do when using red litmious paper to test for ammonium ions

Answer 28

you need to add sodium hydroxide to produce ammonia: | NH4+ + OH- =) NH3 + H2O

Question 29

what indicates a positive result when adding hydrochloric acid to a solution to test for carbonate ions

Answer 29

the carbonate ions will fizz because CO2 is being produced. It will also turn lime water cloudy

Question 30

What can be used to test for alkenes

Answer 30

bromine water

Question 31

What can be used to test for aldehydes

Answer 31

Fehlings or benidicts solution (they oxidise aldehydes but not ketones) or tollings reagent

Question 32

what indicates a positive result when solid sodium carbonate is mixed with a carboxylic acid

Answer 32

The solution will fizz | if bubbled through limewater in a second test tube it will turn it cloudy (CO2 is produced)

Question 33

How do you test for halide ions (chloride, bromide and iodide)

Answer 33

add dilute nitric acid (HNO3) | followed by silver nitrate (AgNO3)

Question 34

how do you prepare tollings reagent

Answer 34

you mix silver nitrate and dilute sodium hydroxide then add drops of ammonia solution

Question 35

write an equation fot the reacton of the carbonate ions with the hydrogen ions when using hydrochloric acid to test for caronate ions

Answer 35

CO3^2-(aq) + 2H+ =) CO2(g) + H2O(l)

Question 36

colour precipitate does chroride give when testing for halide ions

Answer 36

a white precipitate ( of silver chloride)

Question 37

what will be observed when a positive result comes from a test with potassium dichromate to test from primary and secondary alcohols

Answer 37

it turns from an orange solution to a green solution

Question 38

what are flame tests used to identify

Answer 38

group 2 metals

Question 39

in benedicts solution what are the copper ions dissolved in

Answer 39

sodium carbonate

Question 40

in feilings solution what are the copper ions desolved in

Answer 40

sodium hydroxide

Question 41

What other conditions are needed when using potassium dichromate to test for primary and secondary alcohols

Answer 41

Acidified and heat

Question 42

what does a solution turning brick red (from blue) in fehlings or benidicts indicate ?

Answer 42

an aldehyde is present

Question 43

in a flame test what colour does strontium (Sr^2+) burn

Answer 43

red

Question 44

when using dilute hydrochloric acid and barium chloride solution to test for sulfide ions what indicates a positive result

Answer 44

a white precipitate will form

Question 45

write an equation to show how the copper ions in fehlings solution are oxidised when mixed with an aldehydes

Answer 45

Cu^2+ +2OH- + 2e- =) Cu2O + H2O

Question 46

How do you distinguish between primary and secondary alcohols

Answer 46

- oxidise an alcohol under reflux then test for carboxylic acids - oxidse an alcohol under distillation then test for an aldehyde - oxidise an alcohol under reflux then test for a keytone