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Topic: Help with Chem HW question  (Read 242 times)

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Offline hello12345

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Help with Chem HW question
« on: January 05, 2021, 09:35:27 PM »
This is a General Chemistry Question:

A reaction happens with 75 grams of acetic acid (C2O2H4) and an unknown metal, resulting in hydrogen gas and a solid metal with a mass of 113.4 g. What is the unknown metal?

Btw this was a question that I attempted but I'm stuck on a step where im getting that the unknown metal is 43.4 grams but Idk what the metal is since I need the answer to be in g/mol to find on the periodic table

Offline AWK

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Re: Help with Chem HW question
« Reply #1 on: January 05, 2021, 11:29:02 PM »
Students make a lot of mistakes when calculating.
But you can't be helped if we don't see your calculations.
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Offline Borek

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Re: Help with Chem HW question
« Reply #2 on: January 06, 2021, 03:50:00 AM »
an unknown metal, resulting in hydrogen gas and a solid metal

Beware: as posted this doesn't make much sense, I suppose what you mean is that there is a solid produced, not the "solid metal".

In general your starting point is the number of moles of the acetic acid. You need to do some guessing as you don't know what is the valence of the metal.

This is a very poorly thought question, as the metal that fits these numbers doesn't react with the acetic acid :(
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Offline hello12345

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Re: Help with Chem HW question
« Reply #3 on: January 06, 2021, 07:44:18 AM »
Yes, sorry I meant that there is a solid, not a solid metal.

Here is my work:
I calculated the number of grams of hydrogen based off of the number of mols of acetic acid. Since dividing 75 grams by the molar mass of acetic acid (60 g/mol) gives you the number of mols (1.25 g/mol) and we know that for every mol of acetic acid there are 2 mols of h2 so we multiply 1.25 by 2. So we have 2.5 mols of h2, and the molar mass of h2 is 2 g/mol. We multiply both these numbers and we get 5 grams of of h2. Now, we can plug everything back into the equation, and we get that the metal should be 43.4 grams. After converting this to amu (I used an online calculator) you get 26.1 amu, which is closest to aluminum.

Offline AWK

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Re: Help with Chem HW question
« Reply #4 on: January 06, 2021, 08:53:35 AM »
The calculation for hydrogen is completely nonsensical.
1.25 moles of acetic acid, when reacted with metal, can only make 0.625 moles of H2 and no more.
Better check the figures on your problem.
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Offline mjc123

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Re: Help with Chem HW question
« Reply #5 on: January 06, 2021, 10:39:12 AM »
Assuming complete reaction of the acetic acid, 113.4 g is the mass of 1.25 moles of a monoacetate MOAc, or 0.625 moles of a diacetate M(OAc)2, or 0.417 moles of a triacetate M(OAc)3, or...

For each case, work out the molar mass of the metal acetate, subtract the acetate(s) and find the molar mass of the metal. Is there a candidate on the periodic table that makes sense?

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