Answer:
I cannot give you all the answer but I can help you to solve those.
Explanation:
The first question:
How many grams are there in 7.5×
molecules of 
?
So we need to find the molecular mass first, use your periodic table,
And then we can find out 2+32+16×4=98 g/mol
Then, we need to find how many moles, by using Avogadro's constant:
Avogadro's constant: 1 mole = 6.02×
∴
=1.25 mol(2d.p.)
Lastly, find the grams using the formula 
m=Mn
m=1.25*98
m=122.5g
-------------------------------------------------------------------------------------------------------------
In conclusion, use those formula to help you:
(which M = molecular mass(atomic mass) m=mass of the substance and n = moles)
Avogadro's constant: 
From Latin word alumen, mean alum
Answer:
1.48 x 10^47 mol of Na
Explanation:
8.90 x 10^24 atoms of Na (1 mol of Na/6.022 x 10^23 atoms of Na)=
1.48 x 10^47 mol of Na
Answer:
Explanation:
Hello.
In this case, we can see that the mass of carbon of the unknown compound comes from the yielded mass of carbon dioxide, thus, we compute the moles of carbon as follows:
Moreover, the mass of hydrogen comes from the yielded water, therefore we can also compute the moles of water:
Then, to find the subscripts in the empirical formula, we divide by the moles of carbon as the smallest:
Whose molar mass is:
Thus, the ratio of the molecular formula to the empirical formula is:
Therefore, the molecular formula is twice the empirical formula:
Which is actually ethane.
Regards.
