Chemistry A, real simple for most people. Mol problems.

[Fishingaxe]

Chemistry A, real simple for most people. "Mol" problems.

Homework Statement

Hello, first I'd like to say thank you to this community as I have gotten a lot of help in the physics department before and is basically a big reason of me passing the class.

Now chemistry is here and I am having a little bit of trouble so I thought I'd put up a few problems here and you can look over my attempt of solving it and maybe help me along the way.


Problem A) A copper test shows to contain 0.126 mol of copper, the whole test weighs 8.562 g. Does the test contain of 100% copper?



Attempt to solve: n=m/M

n= 8.562g / 0.126*6.02*10^23
n = 8.562 / 7.585*10^22
n = 4.09*10^25.

^--- this is how far I've managed to come on my own. I know the solution is more or less done by now but I am having trouble with what to write, in terms of grams etc to finish off the question. I know that if the answer is not 8.562g the test doesn't contain of 100% copper. As said, don't know how to take it from here.

Problem B) A sugarcube has the mass 2.1g. The sugar is made of sackaros with the formula C₁₁H₂₂O₁₁

a) calculate "n" sackaros in the sugarcube.
b) calculate "n" carbonatoms in the sugarcube.

Attempt to solve: <---- This is where I am completely lost. I know that I have to use the formula n=m/M and I understand what the formula means. What I don't understand is how to get those numbers from "C₁₁H₂₂O₁₁". I am a complete novice when it comes to this. Any help is very much appreciated.





PS: Posted this in another chemistry section in this forum but I've realized that this is the homework section so I apologize.

 

[Saitama]

Attempt to solve: n=m/M

n= 8.562g / 0.126*6.02*10^23
n = 8.562 / 7.585*10^22
n = 4.09*10^25.

How do you get M=0.126*6.02*10^23?? And please define your variables.

Problem B) A sugarcube has the mass 2.1g. The sugar is made of sackaros with the formula C₁₁H₂₂O₁₁

a) calculate "n" sackaros in the sugarcube.
b) calculate "n" carbonatoms in the sugarcube.

Attempt to solve: <---- This is where I am completely lost. I know that I have to use the formula n=m/M and I understand what the formula means. What I don't understand is how to get those numbers from "C₁₁H₂₂O₁₁". I am a complete novice when it comes to this. Any help is very much appreciated.
.

To calculate the moles of sackaros, you need its molar mass. Can you calculate that?

 

[Fishingaxe]

How do you get M=0.126*6.02*10^23?? And please define your variables.



To calculate the moles of sackaros, you need its molar mass. Can you calculate that?

Thank you for helping, I had another thread up here that contained the exact same problems and already solved them with the help from borek and one other person as well.

I am much more familiar with these types of things now :)

 

[Borek]

https://www.physicsforums.com/showthread.php?t=723794

 

[DeeNos]

Hello, it's great to hear that you have found this community helpful in the past! Chemistry can be a challenging subject, but with practice and help from others, you can definitely succeed.

For Problem A, you are on the right track with using the formula n=m/M. However, there are a few things to note:

1. The units for molar mass (M) are g/mol, not just g. So you will need to divide your answer by the molar mass of copper (63.55 g/mol) to get the correct number of moles.

2. The number you calculated, 4.09*10^25, is very large and does not make sense in this context. Remember that moles are a unit of measurement, not a number. So your answer should be in the form of a number of moles, not a number times 10 to the power of something.

3. To determine if the test contains 100% copper, you can compare the number of moles of copper to the total number of moles in the test. Since the test only contains copper, the total number of moles would be the same as the number of moles of copper. So if your answer is 0.126 moles, then the test is 100% copper. If your answer is different, then the test contains something other than copper.

For Problem B, you are correct in using the formula n=m/M. However, you need to know the molar mass of sucrose (C11H22O11) in order to solve this problem. You can find this by adding up the molar masses of each element in the compound. You can find the molar masses of each element by looking at the periodic table.

For part a), once you have the molar mass of sucrose, you can plug that into the formula to calculate the number of moles in the sugar cube. Remember to use the mass of the sugar cube, not just one element.

For part b), you can use the formula n=N/Na, where N is the number of atoms of carbon in the sugar cube and Na is Avogadro's number (6.02*10^23). To find N, you can use the ratio of the subscripts in the molecular formula. In this case, for every 11 carbon atoms, there are 1 molecule of sucrose. So if you know the number of