Core Practical 7 & 15

Question 1

How would you test for acid or base character?

Answer 1

Use indicator paper, blue =base, red = acid

Question 2

How can a flame test be used to identify metal ions?

Answer 2

Dip a nichrome wire in HCl solution. Then into metal ion solution. Hold over blue flame of Bunsen burner and observe the flame colour.

Question 3

Li+ flame colour

Answer 3

red

Question 4

K+ flame colour?

Answer 4

lilac

Question 5

Na+ flame colour?

Answer 5

yellow

Question 6

Ba2+ flame colour?

Answer 6

green

Question 7

Ca2+ flame colour?

Answer 7

brick red

Question 8

Sr2+ flame colour?

Answer 8

crimson

Question 9

Cs+ flame colour?

Answer 9

Blue

Question 10

Rb+ flame colour?

Answer 10

Red

Question 11

Mg2+ flame colour?

Answer 11

No colour

Question 12

How could you test for CO​​3​​2-​​ and HCO​​3​​- ​​ions?

Answer 12

Add to aqueous acid + collect gas (CO2) formed in gas syringe. Then test gas by using delivery tube & bubbling through limewater. If cloudy = CaCO3 precip formed

Question 13

How would you test for NH​​4​​+​​ ions ?

Answer 13

Add aqueous ammonia and gently warm the solution. The gas will turn damp red litmus paper blue

Question 14

How would you test for SO​​4​​2​​−​​ ions?

Answer 14

add dilute HCl (removes traces of carbonate ions) followed by BaCl2 = white precip formed(BaSo4)

Question 15

Test for halides?

Answer 15

Add silver nitrate solution. Cl- = white precip Br- = cream precip and I- = yellow precip

followed by ammonia solution.
Cl- precipitate redissolves, Br- only does in concentrated ammonia solution and I- does NOT

Question 16

Observation of Mg2+ in NaOH? and then in excess?

Answer 16

NaOH: White suspension

add more NaOH: n/a

Question 17

Observation of Ca2+ in NaOH? and then in excess?

Answer 17

NaOH: White suspension (but more soluble than Mg(OH)2

add more NaOH: n/a

Question 18

Observation of Sr2+ and Ba2+ in NaOH? and then in excess?

Answer 18

NaOH:

add more NaOH: n/a

Question 19

Observation of Zn2+ in NaOH? and then in excess?

Answer 19

NaOH: White ppt Zn(OH)2. soluble in NH3. [Zn(NH3)4] 2+ = colourless solution
add more NaOH: ppt dissolves, colourless solution = [Zn(OH)4] 2-

Question 20

Observation of Al3+ in NaOH? and then in excess?

Answer 20

NaOH: White ppt Al(OH)3

add more NaOH: ppt dissolves, colourless solution, [Al(OH)​4]−

Question 21

Observation of Ag+ in NaOH? and then in excess?

Answer 21

NaOH: Ag2O dark brown ppt. soluble in NH3, colourless solution [Ag(NH3)2] +
add more NaOH: ppt doesn’t dissolve

Question 22

Observation of Cu2+ (blue) in NaOH? and then in excess?

Answer 22

NaOH: Blue ppt [Cu(H2O)4(OH)2] soluble in excess NH3 = deep blue solution [Cu(NH3)4]2+
add more NaOH: Ppt doesn’t dissolve

Question 23

Observation of Fe3+ (yellow) in NaOH? and then in excess?

Answer 23

NaOH: Brown ppt Fe(OH)3

add more NaOH: Ppt doesn’t dissolve

Question 24

Observation of Fe2+ (green) in NaOH? and then in excess?

Answer 24

NaOH: White/green ppt slowly turning brown in air (oxidation to Fe(OH)3
add more NaOH: Ppt doesn’t dissolve

Question 25

Observation of Cr3+ (green) in NaOH? and then in excess?

Answer 25

NaOH: Green ppt [Cr(H2O)3(OH)3] soluble in NH3, Cr(NH3)6 3+ violet solution
add more NaOH: ppt dissolves forming [Cr(OH)6]3- green solution

Question 26

Observation of Co2+ (pink) in NaOH? and then in excess?

Answer 26

NaOH: Blue ppt Co(H2O)4(OH)2. Slowly turns pink. dissolves in NH3 [Co(NH3)6]2+ light brown colour. Turns dark brown upon standing- slow oxidation to Co(III)
add more NaOH: ppt doesn’t dissolve

Question 27

Observation of Ni2+ (green) in NaOH? and then in excess?

Answer 27

NaOH: Green ppt Ni(H2O)4(OH)2. Soluble in NH3 = blue solution [Ni(NH3)6] 2+
add more NaOH: Ppt doesn’t dissolve

Question 28

Observation of Mn2+ (pale pink) in NaOH? and then in excess?

Answer 28

NaOH: Off-white ppt, Mn(OH)2 turns brown upon exposure to air (oxidation to MnO2)
add more NaOH: Ppt doesn’t dissolve

Question 29

Bromide + conc H2SO4 observations?

Answer 29

steamy fumes (HBr) 
brown vapour(Br2)
choking fumes (SO2)

Question 30

Chloride + conc H2SO4 observations

Answer 30

Steamy fumes (HCl)

Question 31

Iodide + conc H2SO4 observations?

Answer 31

steamy fumes - HI
black solid -iodine(s)
Purple vapours- I2(g)

Question 32

What colour is [MnO4]-

Answer 32

Violet

Question 33

What colour is [CrO4] 2-

Answer 33

yellow

Question 34

What colour is [Cr2O7]2- ?

Answer 34

orange

Question 35

How can you test for bromide?

Answer 35

Add chlorine water to a solution of bromides. If present orange solution made, with maybe some effervescence

Question 36

Test for alkene?

Answer 36

Add bromine water to compound & shake

orange decolourises if C=C present

Question 37

Test for Oh group? (not phenols)

Answer 37

Add PCl5
misty fumes of HCl produced
Add a small piece of sodium=effervescence

Question 38

Test for carboxylic acids?

Answer 38

add ethanol + conc sulfuric acid
heat in water bath
mix with aqueous sodium carbonate
if carboxylic acid =

Question 39

What is the esterification test?

Answer 39

Gently warm alcohol and carboxylic acid in presence of conc H2SO4
Should produce compound with characteristic smell

Question 40

Test for primary/secondary alcohol and Aldehyde?

Answer 40

Warm with acidified H2SO4 and K2Cr2O7

Colour changes from orange to green

Question 41

What is the Iodoform reaction?

Answer 41

warm with iodine and sodium hydroxide. yellow ppt. antiseptic smell. positive test with methylketones, ethanal, ethanol and methyl secondary alcohols

Question 42

Describe Fehling’s test

Answer 42

Fehling’s solution (copper II ions dissolved in NaOH)
if it’s heated with an aldehyde the blue Cu2+ ions are reduced to a brick-red ppt copper (I) oxide (KETONES DON’T REACT SI SOLUTION STAYS BLUE)

Question 43

How do you test for an aldehyde?

Answer 43

Add tollens reagent & warm

silver mirror = aldehyde present

Question 44

Heating an aldehyde with acidified dichromate ions produces …

Answer 44

carboxylic acid