Could you please explain this chemistry observation, please. Test tomorrow, urgent!?

[匿名]

2018-01-09 11:24 pm

Test is as follows:
Using a measuring cylinder, 25cm3 of distilled water was poured into a polystyrene cup. 4g of solid H was added to the cup and the mixture stirred with a thermometer. The temperature of the mixture was measured for 90 seconds.
Temperature change is -6 deg celsius

This experiment was repeated with solid L. The temp change is 13 deg celsius. A little of the solution was saved for the next exp

next exp :
a little of solution from exp 1 is poured into a test tube and the solution from exp 2( the one that was saved for later) was added in.

Obsv. Rapid effervescence produced

question:
suggestion an explanation for the observation.

Doubt : All I could guess was that it is an acid base reaction.

The mark scheme is as follows
Carbonate(1)
carbon dioxide(1)
acid(1)

Could anyone explain where the carbonate came from?

回答 (1)

戇戇居士

2018-01-09 11:40 pm

✔ 最佳答案

An acid reacts with a carbonate to give carbon dioxide gas.

When the two solutions are mixed, rapid effervescence is produced. It can be deduced that the two solutions are acid and carbonate solutions, and the effervescence is due to formation of carbon dioxide gas.

When solids H and L dissolve in water, the solutions are endothermic and exothermic respectively. It can be deduced that H is a carbonate and L is an acid.

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