A. 1 mol of Na2S The answer is B. 3.0 x #10^24# molecule of O2, why?
B. 3.0 x #10^24# molecule of O2
C. 8.8 x 10 g of NaCl
D. 1.2 x #10^24# atoms of K
A
To calculate the mass of 1 mol of #"Na"_2"S"# we need just to multiply it by it's molar mass: 78,0452 g/mol. Therefore the result will be 78,0452 g.
B
To calculate the mass of #"O"_2#, we first need to divide the result by the Avogadro constant.
#3.0 × 10^24color(white)(l) "molecules O"_2 × "1 mol O"_2/(6.022 × 10^23color(white)(l) "molecules O"_2) = "4.98 mol O"_2#
This gives us the moles of #"O"_2 #.
Then we multiply by the molar mass.
#"4.98 mol O"_2 × "32.00 g O"_2/"1 mol O"_2 = "160 g O"_2#
C
For C we only have 88 g.
D
And for D the molar mass of #"K"# is 39,0983 g/mol.
This means
#1.2 × 10^24color(white)(l) "atoms" × "1 mol"/(6.022 × 10^23color(white)(l) "atoms") × "39.10 g"/"1 mol" = "80 g"#
This question was previously asked in
HTET TGT Mathematics and Science 2012 - 2013 Official Paper
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- 16.0 grams of O2
- 0.8 mole of O2
- 6.02 × 1023 molecules of O2
- 20.4 litre of O2 at STP
Answer (Detailed Solution Below)
Option 3 : 6.02 × 1023 molecules of O2
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The correct answer is 6.02 × 1023 molecules of O2.
Concept:
6.02 x 1023 molecules of O2 has more mass.
Calculation:-
- 16 grams of O2 -
No. of moles = given mass/molar mass = 16 gm / 32 gm = 1/2, Mass of one mole of O2= 2 x atomic mass of O2 = 32 gm, Mass of 16gm of O2 = 1/2 x 32 gm = 16 gm
- 0.8 mole of O2 -
No of moles of O2 = 0.8, Mass of one mole of O2= 2 x atomic mass of O2 = 32 gm, Mass of 0.8 moles of O2 = 0.8 x 32 gm = 25.6 gm
- 6.02 x 1023 molecules of O2 -
No. of moles = given no of particles / Avogadro no = 6.02 x 1023 / 6.02 x 1023 = 1,Mass of 6.02 x 1023 molecules of O2 = 1 x 32 gm = 32 gm
- 20.4 liter of O2 at STP -
No. of moles = given Volume / 22.4 Liter = 20.4 / 22.4 = 0.91, Mass of one mole of O2= 2 x atomic mass of O2 = 32 gm, Mass of 20.4 liter of O2 in STP = 0.911 x 32 gm = 29.14 gm
- In the SI system, mole (symbol, mol) was introduced as the seventh base quantity for the amount of a substance.
- The mole, symbol mol, is the SI unit of the amount of substance. One mole contains exactly 6.02214076× 1023 elementary entities.
- This number is the fixed numerical value of the Avogadro constant, NA, when expressed in the unit mol–1 and is called the Avogadro number.
- The amount of substance, symbol n, of a system is a measure of the number of specified elementary entities.
- An elementary entity may be an atom, a molecule, an ion, an electron, any other particle or specified group of particles.
- It may be emphasized that the mole of a substance always contains the same number of entities, no matter what the substance may be. In order to determine this number precisely, the mass of a carbon–12 atom was determined by a mass spectrometer and found to be equal to 1.992648 × 1023 g. Knowing that one mole of carbon weighs 12 g, the number of atoms in it is equal to = 6 0221367 x 1023 . atoms /mol 2
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