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How can you be sure thermal decomposition is complete?

jenn12345

How can you? It came up on a past paper :smile:

Reply 1

upthegunners

it would depend on what you are thermally decomposing

calcium carbonate

Weighing to constant mass.
In other words, you heat, then weigh
then heat then weigh
until the masses of the contents you achieve are both equal! That tells you that all off the CaCo3 is decomposed and no more mass can be lost through further decomposition (as the co2 leaves).

(edited 10 years ago)

Reply 4

username878045

Original post by jenn12345

calcium carbonate

Was it being decomposed connected to a tube, with the gas being bubbled through? Because the reaction would be over when this system stopped bubbling. Edit: The above poster's technique might work better - it's less complicated.

Reply 5

jenn12345

Thanks, one more thing. What is the balanced equation for calcium oxide and water reacting to make calcium hydroxide
so far i have CaO + H2o -----> Ca(OH)3 +CO2

is this ok?

Reply 6

jenn12345

Original post by PythianLegume

We are not told in the paper

Reply 7

username878045

Original post by jenn12345

Thanks, one more thing. What is the balanced equation for calcium oxide and water reacting to make calcium hydroxide
so far i have CaO + H2o -----> Ca(OH)3 +CO2

is this ok?

Calcium forms 2+ ions, so the product would be Ca(OH)2

Thanks great help

Original post by jenn12345

Thanks great help

The equation is still incorrect with Ca(OH)2 - you have put carbon in the products, but it'snot in the reactants.

Reply 10

RRC

heat to constant mass if the mass of residue is higher than expected i get that but what if the mass is lower than expected could that happen?what would cause it to happen?