I need to find the molecular wieght of potassium aluinum sulfate dodecahydrate (I would type the formula, but I'm not sure how to get it in here. Hopefully that is enough info). What does dodeca mean for one thing.
What I think I am confused about is that in the balanced equation (which is all they give of the molecular formula) there are two of one molecule and 12 waters. Should I reduce that? How many atoms are actually in the molecule?
Sorry my question is not very clear. I'm not even sure what I'm asking, but I know I am totally lost (and I hate chemistry...) Any help would be great.
2006-09-10 16:08:02 · 6 answers · asked by Kiko 3 in Science & Mathematics ➔ Chemistry
But how many water molecules are there in this molecule?
2006-09-10 16:17:07 · update #1
The problem is that I am not sure what my formula should be. They only give the formula in a balanced equation, but I'm not sure if I should reduce the numbers, and stuff like that. I'm doing a really bad job of explaining my problem...
2006-09-10 16:25:20 · update #2
Dodeca is the prefix for 12 , it comes from the greek. Your compound has 12 waters of hydration. Each water molecule has the mass of 18 amu. 18 times 12 = 216 amu from the hydrate portion of the compound.
K Al (SO4) 2 the other part of the compound has one potassium ion ( K ^ +1 ) and it has one aluminum ion ( Al ^ + 3 ) and it also has two sulfate groups each sulfate group has a -2 charge.
potassium 39 amu
Aluminum 27 amu
sulfur 32 amu each times 2 = 64 amu
oxygen 16 amu each times 8 = 128 amu
add all the amu for the non water portion = 258 amu
add the 216 amu from the waters of hydration and you get a total of 474 amu
The gram formula weight for this compound is 474 g
That means that one MOLE of the compound is euqal to 474 g of the compound.
2006-09-10 16:33:20 · answer #1 · answered by Roy G. Biv 3 · 0⤊ 0⤋
Good question!
1. Molecular weight of water (H2O) for example is:
The atomic mass of hydrogen (H) is 1.00784 u and that of oxygen (O) is 15.9994 u; therefore, the molecular mass of water with formula H2O is (2 Ã 1.00784 u) + 15.9994 u = 18.01508 u. So long as you know the formula of the compound you can compute the molecular weight
2. "dodeca" - means “twelve” (Greek)
do is 2 and deca is 10 so 2+10 =12
So there are 12 water molecules.
3. Your questions are clear and you are not lost just a bit overwhelmed. Do not get discouraged just keep on working and get some rest.
4. You need to compute only the molecular weight of 1 molecule of the compound.
2006-09-10 23:11:06 · answer #2 · answered by Edward 7 · 0⤊ 0⤋
Oh dear dont get stressed out. To calculate the molecular weight you need to multiply the amount of molecules in the formula with the mass that's in the periodic table. Just use the molecular formula in the balanced equation, just take into considerarion the amount of each molecule that's present, such as K, Al, S, and H2O.
2006-09-10 23:51:04 · answer #3 · answered by Natasha B 4 · 0⤊ 0⤋
To answer your question, you will need the complete chemical formula and a periodic table. Then find the atomic weight for each type of atom that shows up in the formula on the periodic table and add them all together.
For example, say you want to find the molecular weight of water. The chemical formula H2O means that one molecule of water has 2 hydrogen atoms and one oxygen atom, so you have H + H + O. Look on the periodic table and it says that H = 1.00794 and O = 15.9994. So to find the molecular weight, you would add 1.00794 + 1.00794 + 15.9994 and find that the answer is 18.015.
Follow this same process for the formula that you have and you'll be set. Good Luck!
2006-09-10 23:21:25 · answer #4 · answered by cushdogjr 3 · 0⤊ 1⤋
Dodeca means 12. So the formula of your compound, which is a type of alum crystal, is KAl(SO4)2.12H2O. Adding up the atomic weights of all these atoms gives
39+27=(32+(16x4))x2+12x(2+16)=474 if my arithmetic is right.474
2006-09-10 23:16:40 · answer #5 · answered by zee_prime 6 · 2⤊ 1⤋
Just add up the atomic weights of all he elements in the formula.
Do not hate chemistry. It is nothing but an organize cooking lesson.
2006-09-10 23:15:10 · answer #6 · answered by cherox 3 · 0⤊ 1⤋