Question

When should I use (i) oven, (ii) filter paper and (iii) desiccator for drying?

Answer 1

filter paper when the liquid can be absorbed.. like its not too dense. heating when the substance is not combustible and not too heat-sensitive. and desiscator when the substance is hygroscopic.. so that the desiccator (like silica gel) absorbs water (of crystallisation generally) from the substance.

Answer 2

Sorry, but can you illustrate them with examples?
Like if i have NH4Cl, CaCl2, BaSO4, CuSO4.5H2O, what should I use to dry these salts?

Answer 3

okay CuSO4.5H20 has water of crystallisation. using a desiccator will rob its of water, and it ll become anhydrous and change from blue to white crystals.

NH4Cl is sublimable, so heating it will vaporise it, so no help there. you can use filter paper there.

Am not too sure about the properties of barium sulphate and CaCl2, but as far as I remember, BaSO4 is generally an insoluble precipitate, so filter paper for initial drying, and then heating should do it. As for calcium chloride, i guess it also forms complex compounds with water molecules, like copper sulphate, so a desiccator would be good for it.


Now, let me add that ofcourse desiccator absorbs moisture. so suppose you have precipitated a salt as a filtrate, which had precipitated in a solution, it will be wet. so it is a good idea to use filter paper for most of them, and then proceed to use a desiccator or heat which ever. (oven means general heating here, because a microwave oven will have another thousand limitations)

Answer 4

I know that for BaSO4, we need to use oven, because i've done that experiment.
for NH4Cl, that makes sense

For CuSO4.5H20, i still don't understand, what method should i use?

Another problem, to dry the gas what method should i use? for example, SO2, NH3, Cl2 and CO2

Answer 5

this calls for @diya .

see what a desiccator is. its a substance that has a very high affinity for absorbing water. so. if you put the crystals on a surface with silica gel, which is a desiccator, it dehydrates the ".5H2O".

and too be honest, the first time i came across the word desiccator, was in your question. i googled up, read about it, and answered this, so I may not be totally right.

Answer 6

as for drying the gases.. I believe you mean absorbing moisture... so passing the gas through a dehydrating environment may help. @diyadiya.. help!!

Answer 7

Then, if i want to get the hydrated CuSO4.5H2O, i should not use disiccator, right?

Dehydrating environment is too broad.... :S

Answer 8

i think it is the best, as desiccator dehydrates the water of crystallisation as well.

Answer 9

Hmm... wouldn't it dehydrate the salt? I want the hydrated one ....

Answer 10

To get the hydrated salt from the dehydrated one, just add water. White CuSO4 turns into blue CuS04.5H20 ;)
And as apoorv said, a dehydrating agent, which wouldn't react with the substance to be dried, can be used to dry the gases. Preferably conc. H2SO4(conc. H2S04 is less reactive than dilute H2S04 because it is less acidic.

Answer 11

Nope. I meant I have some wet CuS04.5H20, I want to dry it, what should I do?

Answer 12

Of course, without dehydrating it

Answer 13

Oh then just evaporating would do.(placing in the sun). You should not boil though, because you might risk losing your water of crystallization.

Answer 14

There are various other methods of drying too:
http://en.wikipedia.org/wiki/Drying

Answer 15

Hmm... what about drying the gases?

Answer 16

I just found out that activated alumina( http://en.wikipedia.org/wiki/Activated_alumina) is a very good adsorbate(i.e it adsorbs) of water vapour from wet gases. Do you've to do this practically?

Answer 17

lol. The questions I asked is probably exam-based.

Answer 18

In my mock exam, we needed to suggest an experimental set-up to collect SO2 from a reaction. The drying agent used there is conc. H2SO4

Answer 19

That reminds me that I must know how to dry all the gases (at least the common one)

Answer 20

In my book, I've written CaCl2 is not used to dry NH3.
But I'm not sure for the rest of the gases, like CO2, Cl2

Answer 21

Okay there is another thing. If you have studied eudiometry, you 'll know that there are various substances and compounds which absorb various gases (hence separate gases). Although it's not ecactly "drying", but it may help you.

Answer 22

Hmm, sorry... I haven't studied that yet

Answer 23

BTW, the question in my mock exam is like this
(See question 8)

Answer 24

Conc. H2S04 is good for S02 because it doesn't react with it.
Honestly, I think that this is the most boring part of Chemistry, unless we get the chance to do it practically. :P

Answer 25

When we do experiment.... That would be the school-based assessments. Otherwise, we rarely do experiment in Chem lessons
The problem is when should I use conc. H2SO4?

Answer 26

to dry any gases except ammonia.

Answer 27

Wow~ That's clear! Thanks!

Answer 28

np :)

Answer 29

I suddenly envy @callisto 's handwriting so much! x)

Answer 30

My handwriting is poor... Sometimes I can't read it :S