Complete the sentences below by doing the mole calculations:

i)In $\pu{20 mol}$ of copper(II) phosphate, there are ______$\pu{mol}$ of copper ions and ______$\pu{mol}$ of oxygen atoms.

ii)A sample that contains $1.8 \times 10^{23}$ atoms of lead has a mass of ______$\pu{g}$.

iii)A gold crown that contains $7.95 \times 10^{22}$ atoms of gold has______$\pu{mol}$.

These questions are from TopHat, if anyone can help me that would be awesome.

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    $\begingroup$ I’m voting to close this question because, like your professor, we feel you should learn the material by doing it yourself. $\endgroup$ Oct 1, 2020 at 1:00
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    $\begingroup$ In a crammed class of 100-300 how can professors manage to ensure that each and every student is following them? Worse, if the classes are online. The attention span of younger students is hardly 10-20 min. Too many distractions and no habit of taking notes. Above it, many lazy teachers provide them with PowerPoint print "notes". $\endgroup$
    – AChem
    Oct 1, 2020 at 1:17
  • $\begingroup$ Actually, you should learn these in high school. Google "mole concept" and you will realize these are pretty straight forward math question once you realize what is Copper(II) phosphate [you can google that too]. $\endgroup$
    – SamL
    Oct 1, 2020 at 1:39
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    $\begingroup$ This is not a title to a question. A title should reflect the body of the question (in this case, there is none). $\endgroup$ Oct 1, 2020 at 4:13

1 Answer 1


You only need to know how to write chemical formulae and know two facts:

I) 1 mole of a substance equals it atomic or molecular weight. II) 1 mole of a substance has $\ce{6.02×10^23}$ particles or units.

Think of moles like a dozen. Have you eaten a double-yolked eggs by chance?

If we buy 1 dozen double yolked eggs, how many eggs yolks will be there: 12 x 2 =24.

If you have 20 mole of $\ce{CuCl2}$ unit, there are 20 moles of Cu atoms and 2x20 moles of Cl atoms. In order to solve copper phosphate, you need to know how to write the formula of copper phosphate.

Also, develop a habit of opening textbooks. If you only rely the "web" and on the professor, they will not take you anywhere. Textbook's solved examples are a great resource which modern students rarely bother to read.

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    $\begingroup$ I always like to have two or three books for the same topic. Reading the slightly different worded explanations from different authors really helps understanding. $\endgroup$
    – MaxW
    Oct 1, 2020 at 18:31
  • $\begingroup$ Certainly, this should be the habit of any serious student of science whether he is a teenager or 80 year old retired scientist. $\endgroup$
    – AChem
    Oct 2, 2020 at 1:10

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