Textbook fundamentals QE.9

[Tala Ayoub 1H]

Epsom salts consist of magnesium sulfate heptahydrate. Write its formula. (a) How many atoms of oxygen are in 5.15 g of Epsom salts? (b) How many formula units of the compound are present in 5.15 g? (c) How many moles of water molecules are in 5.15 g of Epsom salts?

How do we know the formula of magnesium sulfate heptahydrate in this question?

[ashna kumar 3k]

I believe that while the textbook may have expected us to be able to come up with the formula based on the name of a substance, we haven't learned how to do that yet in our course and on our test and on our midterm, all the molecular formulas in our questions will be given to us. However, if we did want to figure the formula for magnesium sulfate heptahydrate, we would have to know that sulfate was SO4 2- and magnesium's charge is 2- which makes magnesium sulfate MgSO4. The prefix hepta- is 7 and hydrate indicates H2O, so our full formula would be MgSO4.7H2O.

We would have to have prior knowledge in order to figure out the molecular formula from the name.

Hope this helps!

[Kiku Shirakata 2A]

Once we determine the formula of magnesium sulfate heptahydrate, MgSO4.7H2O, you can figure out the answers to the other parts of the question. For example, in part a, to find the atoms of oxygen we need to find how many moles of the magnesium heptahydrate from the sample there is so we divide the given mass of the sample by the molar mass. Then we can multiply the mole ratio to find the number of moles of oxygen. Lastly, we multiply by Avogadro's number to find out how many oxygen atoms there is.

[sadiebrebes]

Once we determine the formula of magnesium sulfate heptahydrate, MgSO4.7H2O, you can figure out the answers to the other parts of the question. For example, in part a, to find the atoms of oxygen we need to find how many moles of the magnesium heptahydrate from the sample there is so we divide the given mass of the sample by the molar mass. Then we can multiply the mole ratio to find the number of moles of oxygen. Lastly, we multiply by Avogadro's number to find out how many oxygen atoms there is.

What do you mean by multiply the mole ratio, the ratio being 1:1:4? Or is there other calculation we have to do to find this ratio?

[Nathalia Garibay 1D]

Epsom salts consist of magnesium sulfate heptahydrate. Write its formula. (a) How many atoms of oxygen are in 5.15 g of Epsom salts? (b) How many formula units of the compound are present in 5.15 g? (c) How many moles of water molecules are in 5.15 g of Epsom salts?

How do we know the formula of magnesium sulfate heptahydrate in this question?

I don't think Lavelle expects us to know how to find the formula of Magnesium sulfate heptahydrate just yet because we have not learned it in class. For this problem, you can just search it up.