How many grams of Al2(SO4)3 are needed to prepare 250.0 mL of a 0.400 M Al2(SO4)3 solution?
Details please...I havent learned this and my teacher just threw it in my face. Thanks!!
2006-11-28 05:47:32 · 5 answers · asked by Anonymous in Science & Mathematics ➔ Chemistry
All right, you know what M means, right? It's short for moles per liter. You want to have 0.250 moles of Al2(SO4)3 in each liter of solution. You're preparing 0.4 L of solution, so you need (0.4 * 0.250) = 0.1 moles of Al(SO4)3.
Now the molar mass of each element is listed on most periodic tables. That's how much one mole of that atom weighs. A molecule weighs as much as all the atoms in it put together, so a mole of Al2(SO4)3 weighs as much as two moles of Al, 3 moles of S and 12 moles of O. That's 2(26.982) + 3(32.06) + 12(15.999), according to my periodic table. So if you add it all up, a mole of Al2(SO4)3 weighs 342.132 grams. You only need a tenth of a mole, so you use 34.2132 grams.
2006-11-28 05:58:37 · answer #1 · answered by Amy F 5 · 0⤊ 0⤋
Ok, this should be correct. What you are going to do is change mL to grams. First, change mL into Liters
250mL x (1L / 1000mL) = A. mL cancel and you have Liters.
Next, use the molarity conversion factor. .400M = (.4mol / 1L)
A x (.4mol / 1L) = B. now, your answer is in moles, L cancel.
Now, you will use the Molar mass converstion factor. MM of Al2(SO4)3 = 630.4 g/mol.
B x (630.4g / 1mol) = C This is in grams, and is also your answer.
2006-11-28 14:00:57 · answer #2 · answered by joshua_luttrall 2 · 0⤊ 0⤋
You really need to do your own homework...but here is a hint...
0.4000 M is 0.400 mol/L
You are given a volume. From that you can calculate moles. From there, using the periodic table, add the atoms for the molecular weight of the salt then convert moles to grams.
(edit) Oh well. As I was typing this someone else answered it.
2006-11-28 13:57:32 · answer #3 · answered by Thundercat 7 · 0⤊ 0⤋
alright, so M=mols/L so first you want to find out how many mols of al sulfate are in a .4 molar solution. To do that you multiply 0.4 mol/L by your volume in L (0.25L). That way, the L will cancel out and you will be left with a number in mols. Then to convert from mols to grams you multiply the number of mols by the molecular mass of Al sulfate. YOu find the molecular mass by adding the atomic mass of all of the elements in the molecule.
2006-11-28 13:56:40 · answer #4 · answered by anon 4 · 0⤊ 0⤋
Molecular weight of Al2(SO4)3 = 342.2 g/mol.
Therefore, 1 M solution = 342.2 g/L.
So, 0.400 M = 0.400 * 342.2 g/L
Thus, 250.0 mL of this contains 0.400 * 342.2 / 4 g
= 34.22 g
2006-11-28 14:06:39 · answer #5 · answered by falzoon 7 · 0⤊ 0⤋