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Chemistry paper 5

cruduxcruo9

Hi, need help understanding what is happening in the experiment.

(edited 4 years ago)

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Reply 1

username4648086

Original post by cruduxcruo9

Hi, need help understanding what is happening in the experiment.

They want to confirm whether magnesium oxide is MgO
To know this, we need to have masses of Mg and O so we can verify if the ratio is 1:1
Through experiment we know the mass MgO and Mg, hence we're able to calculate mass of oxygen reacted.

Reply 2

cruduxcruo9

Original post by lyer_in_hellfyre

First they're oxidising Mg by letting air in and heating, which forms MgO I believe. Why are they heating for the second time?

Reply 3

username4648086

Original post by cruduxcruo9

First they're oxidising Mg by letting air in and heating, which forms MgO I believe. Why are they heating for the second time?

Yep.
To remove the water of crystallisation (its usually present in ionic salts)

Reply 4

cruduxcruo9

Original post by lyer_in_hellfyre

Yep.
To remove the water of crystallisation (its usually present in ionic salts)

I have a few questions.

-In point 4 and 5 in the given instructions, it says while you're heating the Mg ribbon in the crucible, periodically lift the lid but each time the lid is lifted, take care to minimise the loss of any white smoke which is some of the powder formed.

I assume we lift the lid to allow air in to react with Mg to produce O2, and the white smoke escaping is the formed MgO?

-when the reaction appears to have stopped, remove the crucible lid and heat the crucible and its contents strongly for 2 minutes.

Does this mean the white smoke formed above is MgO.H2O? Hydrated magnesium oxide? And by heating it we produce pure MgO?

I'd highly appreciate your confirmation and any correction. :smile:

One last thing actually, how to determine the mass of MgO for student 4 in the table? I'm stuck.

(edited 4 years ago)

Reply 5

username4648086

Original post by cruduxcruo9

I assume we lift the lid to allow air in to react with Mg to produce O2, and the white smoke escaping is the formed MgO?

when the reaction appears to have stopped, remove the crucible lid and heat the crucible and its contents strongly for 2 minutes.

Does this mean the white smoke formed above is MgO.H2O? Hydrated magnesium oxide? And by heating it we produce pure MgO?

I'd highly appreciate your confirmation and any correction. :smile:

One last thing actually, how to determine the mass of MgO for student 4 in the table? I'm stuck.

I believe the white smoke formed is hydrated salt as you've rightly mentioned. And yep, by heating it more extremely water of crystallisation is lost, and more pure MgO formed . (: thanks to ya i got to revise!

check how the mass of MgO is calculated for other students (for eg i took student 2...we know sum of mass of crucible and magnesium oxide. We also know the mass of crucible... guess what happens next?)