Lets say I have a 20.0 gram sample of aluminum, how many atoms of aluminum do I have. Im having a hard time figuring this out. Please help.
2007-10-31 06:57:19 · 3 answers · asked by Anonymous in Science & Mathematics ➔ Chemistry
Ok, but i dont fully understanf how you got that.
2007-10-31 07:29:28 · update #1
Al MW = 26.981 g/mole
20.0 g Al = 20.0 g * mole/ 26.981 g = 0.749 moles
0.749 moles * 6.023*10^23 atoms/mole =
= 4.51 *10^23 atoms Al
2007-10-31 07:02:33 · answer #1 · answered by Dr Dave P 7 · 0⤊ 0⤋
First you have to convert the grams into moles. A mole is just a very large number (6.02 x 10^23).
Think about another number you are familiar with -- a dozen. If someone tells you they 20g of pennies can you tell them how many dozen they have? Not without knowing how much a dozen weighs. The molecular weight of an atom or a compound is the number of grams in a mole.
Take 20.0g and divide by the molecular weight (26.98 grams per mole) is 0.74 moles of aluminum. Multiply this # by the number of atoms in a mole, 6.02 x 10^23 which gives you 4.46 x 10^23.
You have to keep the number of significant figures the same (3 in the 20.0), so it is 4.46 x 10^23 atoms.
2007-10-31 16:07:43 · answer #2 · answered by Rush is a band 7 · 0⤊ 0⤋
Ar for Al =27
firstly, find the number of mol of Al
no.mol=20g/27
=0.7407 mol
no of Al atoms
=0.7407 X (6.02 X 10^23)
=4.459 X10^23
to understand this topic you must know the relationship between no of mol with mass of element/volume/and...... sorry i dont remember the another one
2007-10-31 14:40:24 · answer #3 · answered by Myra 1 · 0⤊ 0⤋