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/sci/ - Science & Math

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6189699 No.6189699 [Reply] [Original]

Please /sci/ help a freshman chemfag out, this ain't even homework, I'm just preparing for a test.

A 2g sample containing Cu and Mg is treated with a HCl aqueous solution. 7.48*10^(-3) mol of hidrogen H2 are produced. What's the percentage of Mg and Cu in the sample?

>> No.6189714

>>6189699
>preparing for an exam
>not knowing this

enjoy your career in McDonalds. also, exam or not, this is still a homework thread.

>> No.6189740

>>6189714

I'm sorry but this is bugging me and I know it's probably some trivial shit that I'm missing. Can you lend me a hand?

I know how Cu and Mg would react with the acid but I'm not sure what to do with two reactions

>> No.6189810

Mg (s) + 2HCl (aq)-->MgCl2 (aq) + H2 (g)
Cu (s) + HCl (aq) -->No Reaction

You're supplied exactly how many moles of H2 are present. Use your mole ratio from the original equation (1 mol Mg:1 mol H2) because all H2 formed can be assumed to be from this reaction.

7.48X10^-3 mol of H2 (1 mol Mg/1 mol H2) (40.34 g/mol)=.302 grams of Mg.

Everything else in the sample is Cu, as it contains only Mg and Cu. I think you can calculate your mass percentages from here.

Now use your mole ratio from the initial reaction of 1 mol of H2 (2 mol of H) for every mol of Mg present

>> No.6189814

>>6189810
Ignore that last sentence, just a carry over. Everything else is what you need to do, though.

>> No.6189837

>>6189810

Thank you so much, so the Cu doesn't react because its normal potential is higher?

>> No.6189861
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6189861

>>6189837
Essentially, for simplicity, you can reference the reactivity series. As you go up, the elements are "more reactive", which is to say, they'll be more likely to displace a lower element in, say, a single replacement reaction as above.


This also relates to how easily these elements will form positive ions, or how powerful of a reducing agent they are.

>> No.6189866

>>6189837
some of the Cu will in fact react, but it is neglible with respect to he Mg. you dont need to worry about this stuff until later, just know that it does happen.

>> No.6189878

What the hell man, this is some basic high school stuff. Do they just allow anyone into college over there?

>> No.6191066

>>6189699
>chemistry
>real science

your almost as pathetic as biologists

>> No.6191112

>>6191066
>what are drugs