The-MOLE
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The natural substance with the LEAST MASS is
H2, hydrogen, with a mass of 2.0156 atomic mass units. Recall that each H atom has 1.0078 atomic mass units. By definition, 1 mole of H2, hydrogen, has a mass of 2.0156 g (usually rounded to 2.02 g). How many grams is 1 molecule of hydrogen gas?
3
That once one “combining mass” of an element was known, it must have the Same number of atoms as one combining mass of a different element. By the end of the nineteenth century, the SIZE of that number had been determined And a word, meaning “a heap” had been invented as the unit for that number. AVOGADRO’S NUMBER: 6.02 x 1023 = 1 mole
= 3.34x1024gH2 1moleculeH2
= 1.67x1024gH
6.0
2.20gH2 2x1023Molecu
le2sH=
1atomH
6
Review
What number represents a mole? Avogadro’s number Gram formula mass divided by the Avogadro number = representative particle mass in grams. A representative particle mass will have an exponent in the 10-23 g. range (possibly as big as 10-22 g)
EXPECT information to be missing from problems:
Look for missing info in the text, other problems or sample problems, previous chapters, tables in same or previous chapters, and reference tables including of course the Periodic Table.
8
Problem solving in quantitative chemical problems.
Must use common sense; troubleshoot obvious errors by making sure that inverses have not been used as conversion factors.
If you could put a large number of the same object on the balance, you could get a measurable mass. Then, by dividing this measurable mass by the number of objects, you would get the mass of one individual object. This idea occurred to Avogadro, an Italian scientist who did not know how large the number would be, but who hypothesized
The MOLE
Introduction to stoichiometry
1
AVOGADRO’S NUMBER
How would you find the mass of an object with too little mass to register on your balance?
2
AVOGADRO'S Number
7
REVIEW
KINDS OF REPRESENTATIVE PARTICLES: ions, atoms, molecules, formula units. So if we are referring to 1020 particles, or larger number of particles, we are talking about 10-3 or larger number of moles. The least number of grams of a naturally occurring substance is 2.02 grams/mole, which is H2.
9
For example in practice prob. 1
Find data about apples per bushel.
Found on p 172: 1 doz apples/ .20 bushel
12 apples / dozen
12 apples/ .20 bushels = x apples/.50 bushels.
5
Finding tecule of H2 and 1 atom of H:
21m .02go.pH l2.r6.02.02x12g02H 3r2.p.
Since molecules are the representative particles of hydrogen gas
The question asks about the 2 mass of .50 bushel. Mass of 1 apple, found in sample prob 7.1. Number of apples -> mass of apples. 2.0 kg / 12 apples 12ap/.20 bu=x ap/.50 bu X ap=12ap(.5bu) /.2bu X =30 ap 30 ap/y kb = 12 ap/2.0 kg 12 ap(y kg)= 30 ap(2 kg) 10
The natural substance with the LEAST MASS is
H2, hydrogen, with a mass of 2.0156 atomic mass units. Recall that each H atom has 1.0078 atomic mass units. By definition, 1 mole of H2, hydrogen, has a mass of 2.0156 g (usually rounded to 2.02 g). How many grams is 1 molecule of hydrogen gas?
3
That once one “combining mass” of an element was known, it must have the Same number of atoms as one combining mass of a different element. By the end of the nineteenth century, the SIZE of that number had been determined And a word, meaning “a heap” had been invented as the unit for that number. AVOGADRO’S NUMBER: 6.02 x 1023 = 1 mole
= 3.34x1024gH2 1moleculeH2
= 1.67x1024gH
6.0
2.20gH2 2x1023Molecu
le2sH=
1atomH
6
Review
What number represents a mole? Avogadro’s number Gram formula mass divided by the Avogadro number = representative particle mass in grams. A representative particle mass will have an exponent in the 10-23 g. range (possibly as big as 10-22 g)
EXPECT information to be missing from problems:
Look for missing info in the text, other problems or sample problems, previous chapters, tables in same or previous chapters, and reference tables including of course the Periodic Table.
8
Problem solving in quantitative chemical problems.
Must use common sense; troubleshoot obvious errors by making sure that inverses have not been used as conversion factors.
If you could put a large number of the same object on the balance, you could get a measurable mass. Then, by dividing this measurable mass by the number of objects, you would get the mass of one individual object. This idea occurred to Avogadro, an Italian scientist who did not know how large the number would be, but who hypothesized
The MOLE
Introduction to stoichiometry
1
AVOGADRO’S NUMBER
How would you find the mass of an object with too little mass to register on your balance?
2
AVOGADRO'S Number
7
REVIEW
KINDS OF REPRESENTATIVE PARTICLES: ions, atoms, molecules, formula units. So if we are referring to 1020 particles, or larger number of particles, we are talking about 10-3 or larger number of moles. The least number of grams of a naturally occurring substance is 2.02 grams/mole, which is H2.
9
For example in practice prob. 1
Find data about apples per bushel.
Found on p 172: 1 doz apples/ .20 bushel
12 apples / dozen
12 apples/ .20 bushels = x apples/.50 bushels.
5
Finding tecule of H2 and 1 atom of H:
21m .02go.pH l2.r6.02.02x12g02H 3r2.p.
Since molecules are the representative particles of hydrogen gas
The question asks about the 2 mass of .50 bushel. Mass of 1 apple, found in sample prob 7.1. Number of apples -> mass of apples. 2.0 kg / 12 apples 12ap/.20 bu=x ap/.50 bu X ap=12ap(.5bu) /.2bu X =30 ap 30 ap/y kb = 12 ap/2.0 kg 12 ap(y kg)= 30 ap(2 kg) 10