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Year 11 Chem

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squance:
My sister is going to start yr 11 chem next year and she was just reading ahead in her textbook..

She has some questions that she is stuck on....

I did chem but I forgot the majority of the stuff so I was wondering if some of you guys can help me....

"When 2.8g of magnesium reacts with 50g of HCl solution, the remaining solution weighs 52.6g. Why does the law of conservation of mass seem not to apply in this case?"

and....

This reaction...

NH3(g) + HCl(g) -----> NH4Cl (s)
Is it a precipitation, combination, or neutralisation reaction?? Explain why..

Thanks

Collin Li:

--- Quote from: squance on December 27, 2007, 12:41:02 pm ---When 2.8g of magnesium reacts with 50g of HCl solution, the remaining solution weighs 52.6g. Why does the law of conservation of mass seem not to apply in this case?

--- End quote ---



Hydrogen gas is formed, which will just escape into the atmosphere, so although there is less mass in the end, it is because 0.2g of hydrogen gas has been formed and escaped.

Collin Li:

--- Quote from: squance on December 27, 2007, 12:41:02 pm ---NH3(g) + HCl(g) -----> NH4Cl (s)
Is it a precipitation, combination, or neutralisation reaction?? Explain why.

--- End quote ---

It is both a combination reaction and a neutralisation reaction.
* combination reaction: two reactants have combined to form one product
* neutralisation reaction: an acid, hydrogen chloride, and a base, ammonia gas, react to form a neutral ionic compound.

It is not a precipitation reaction, because the solid has not been formed from solution.

squance:
Thank you !

bec:
I'm doing yr 12 chem next year and I've got a question too...
in a reaction between iron (III) oxide and carbon monoxide, how do we know what the products are?
initially i put:
Fe2O3 + CO --> 2Fe + CO2 + O2

but in the solutions it had it as:
Fe2O3 + 3CO --> 2Fe + 3CO2

Why was my answer wrong? Any explanations about this would be really appreciated because there's obviously something I'm missing here!
thanks!

edit: hahaha i just realised i'd written that i'm doing yr 11 chem next year.. living in the past!! i meant year 12...which means i'm also in the wrong thread...sorry!

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