A sample of lithium sulfate, Li2SO4, contains 6.78 x 10^23 formula units.
a) How many moles of Li+ ions are there in the sample?
b) How many moles of ions are there in the sample?
My work.
I think a) is 2.26 is that correct?
I think Damon worked this below.
To find the number of moles of Li+ ions in the sample, you can use the Avogadro's number and the formula of lithium sulfate.
First, determine the molar mass of Li2SO4.
Li has a molar mass of approximately 6.94 g/mol, S has a molar mass of approximately 32.07 g/mol, and O has a molar mass of approximately 16.00 g/mol.
Molar mass of Li2SO4 = (2 x Li molar mass) + S molar mass + (4 x O molar mass)
= (2 x 6.94 g/mol) + 32.07 g/mol + (4 x 16.00 g/mol)
= 109.94 g/mol
Next, convert the given number of formula units (6.78 x 10^23) into moles.
Moles of Li2SO4 = Number of formula units / Avogadro's number
= (6.78 x 10^23) / (6.022 x 10^23)
= 1.125 moles (rounded to three decimal places)
Finally, since there is a 2:1 ratio between Li2SO4 and Li+ ions, the number of moles of Li+ ions will be half the number of moles of Li2SO4.
a) Moles of Li+ ions = (1.125 moles Li2SO4) * (1/2)
= 0.5625 moles (rounded to four decimal places)
So, the correct answer for part a) is 0.5625 moles.
For part b), you are asked to find the total number of moles of ions in the sample. To do this, simply add the number of moles of Li+ ions to the number of moles of Sulfate (SO4^2-) ions.
In one mole of Li2SO4, there is one mole of Li+ ions and one mole of SO4^2- ions.
Therefore, the number of moles of ions in the sample will be:
b) Moles of ions = Moles of Li+ ions + Moles of SO4^2- ions
= 0.5625 moles + 0.5625 moles
= 1.125 moles
So, the correct answer for part b) is 1.125 moles.