a. How many atoms are present if the substance is lead metal, Pb?
b. How many molecules are present if the substance is sucrose, C12H22O11?
c. How many formula units are present if the substance is calcium carbonate, CaCO3?
This is a question I have to turn in tommorow at school. I've looked in my book, but it doesn't explain how I answer this question. Please help! I'll choose the best answer quickly, I promise!
2007-11-01 06:16:41 · 2 answers · asked by Anonymous in Science & Mathematics ➔ Chemistry
2.64E23
A mole is a number.
Unfortunately, this is never made as clear as it ought to be in most chemistry cources. "PI" is also a number, and everyone is probably famaliar with fractions of "PI" and perhaps even with what they represent in "degrees". PI/2 is 90 degrees, for example.
With "moles" it is different. Ironically, it is because actual "moles" are never used in "working" chemistry. No chemist earns money counting individual atoms. Chemists weigh things, and then express the weight in moles.
A "mole" is approximately 602000000000000000000000. This many atoms of a particular substance has a characteristic weight. Based on the weight, the amount of any substance can be expressed in terms of the number of moles.
Therefore, 0.44 moles of lead atoms is the same as 0.44 moles of hampsters. The answer is 264800000000000000000000. Chemists usually express such large numbers in "fortran" notation. It consists of a fraction, followed by ten raised to a certain power. In the case of the hampsters, it would be 2.64E23.
Due to the equivalence of lead and hampsters, the answer to the second question is also the same, 0.44 moles of sucrose molecules (never mind the empirical formula!) is 2.64E23 molecules.
"Formula units" is a purely achedemic term. I left school 20 years ago and have never used it since. Therefore, I take the meaning to be "molecules". Lead, hampsters, sucrose molecules and "formula units" - the answer is all the same. 0.44 moles of ANYTHING is 2.64E23 THINGS.
What all this has to do with the price of eggs in China:
The price of Chineese eggs reflects the quality of the product. Let's say Chineese eggs all had 0.123456 moles of lead per egg. (They paint the eggs white). How many grams of lead is present in each egg? To answer the question, just look up the molecular weight of lead in a periodic table (it's 207.2 grams per MOLE). This means there are 207.2 grams/mole times 0.123456 moles/egg. The answer is therefore 25.58 grams/egg. Wow! Over an ounce of lead/egg. Let's hope the price of eggs/ounce is higher than the price of lead/ounce........
This is how chemistry works in the real world.
2007-11-01 06:55:50 · answer #1 · answered by Roger S 7 · 1⤊ 0⤋
a. 0.44molPb x 6.02x10^23atomPb/1molPb = 2.65 x 10^23 atoms Pb
b. The same: 6.02x10^23moleculesS/1molS
c. The same 6.02x10^23fuCaCO3/1molCaCO3
2007-11-01 06:34:15 · answer #2 · answered by steve_geo1 7 · 0⤊ 0⤋