Self Test E.5B

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luludaly2B
Posts: 88
Joined: Wed Sep 30, 2020 9:42 pm
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Self Test E.5B

Postby luludaly2B » Tue Oct 06, 2020 9:23 am

Technically this problem wasn't really assigned, but I was reading through the textbook and thought I would complete the self-test problems as well, just to get some extra practice. The question is:
"Calculate the amount of Ca(OH)2 formula units in 1.00 kg of slaked lime (calcium hydroxide), which is used to adjust the acidity of soils."
The answer is not in the answer key, so I just wanted to make sure I was doing it right. First I converted 1.00 kg to 1000 g, then I calculated the molar mass of Ca(OH)2, and got 74.096 g.mol(-1). Then I divided the mass of the sample (1000 g) by the molar mass (74.096 g.mol(-1)). My final answer was 13.5 moles of Ca(OH)2. Can someone double check my answer and correct me if I'm wrong? Thank you!

Bailey Giovanoli 1L
Posts: 107
Joined: Wed Sep 30, 2020 9:50 pm

Re: Self Test E.5B

Postby Bailey Giovanoli 1L » Tue Oct 06, 2020 9:45 am

I did the problem and I got the same answer, 13.5 moles. However, my question is what are the units. It asks for formula units. Is that just moles? I think it might be the number atoms, because those are formula units. So therefore, you would need to convert it to number of atoms using 6.022 x 10^23. Hope this helped at least a little!!

Justin Nguyen 3E
Posts: 87
Joined: Wed Sep 30, 2020 9:35 pm

Re: Self Test E.5B

Postby Justin Nguyen 3E » Tue Oct 06, 2020 10:18 am

I think you're right that formula units are just the number of atoms/molecules, so you would just multiply it by Avogadro's Number (6.022*10^23)

David Chibukhchian 2G
Posts: 154
Joined: Wed Sep 30, 2020 9:50 pm

Re: Self Test E.5B

Postby David Chibukhchian 2G » Tue Oct 06, 2020 10:56 am

I was also confused about whether "formula units" asks for moles or the actual quantity (as in using Avogadro's number). I believe that when the question asks you to find the "amount" of formula units, then it wants you to find moles. However, when the question asks for the "number" of formula units, then it wants the actual quantity that you'd find by multiplying moles with Avogadro's number. This is what I assume based off of the answers to some of the textbook problems in this section and the corresponding question type. However, I'm not too certain. In general, though, I think the word "amount" is associated with moles which is why I think that in this case, moles might be the correct form.


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