28.2 practical techniques

Question 1

steps for recrystallisation?

Answer 1

dissolve in hot water/solvent

add minimum amount of solvent

cool, filter and leave to dry

Question 2

equipment for filtration under reduced pressure?

Answer 2

buchner funnel
buchner flask
pressure tubing
filter paper
vaccum pump

Question 3

steps for filtration under reduced pressure?

Answer 3

attach equipment together

switch on vacuum pump/tap

check for good suction

place filter paper in funnel

slowly pour reaction mixture into filter paper

use distilled water to rinse out the beaker

leave to dry

Question 4

how can you identify a carbonyl compound without the need for spectroscopy?

Answer 4

react with 2-4 DNP and an orange ppt will form

recrystallise orange precipitate

find the melting point

compare with known values

Question 5

why is minimum hot solvent added?

Answer 5

to ensure that the yield of product is not compromised
there will be some solid dissolved in the cold water