1.
How many grams are there in 1.3846 x 10^{24} atom of Silicon?
Correct Answer
A. 64.607 g
Explanation
To change from atoms to grams requires TWO steps:
1st: Change to moles: Take your atoms and DIVIDE by Avogadro’s number:
1.3846 x 10^24 divided by 6.02 x 10^23 = 2.3 moles
2nd: Change to grams: Take your moles and MULTIPLY by molar mass:
2.3 moles x 28.09 g/mol = 64.607 g
2.
How many grams are there in 2.0468 x 10^{25} atoms of NaCl? (The molar mass of NaCl is 58.44g)
Correct Answer
C. 1986.96g
Explanation
Stoichiometry:
(2.0468 x 10^25) x (1 mole/6.02 x 10^23) x (58.44g/mol) =
OR as two steps:
To change from atoms to grams requires TWO steps:
1st: Change to moles: Take your atoms and DIVIDE by Avogadro’s number:
2.0468 x 10^25divided by 6.02 x 10^23 = 34 moles
2nd: Change to grams: Take your moles and MULTIPLY by molar mass:
34 moles x 58.44g/mol =
3.
How many grams are in 2.2274 x 10^{25} atoms of CO_{2}?
Correct Answer
A. 1,629 g
Explanation
Firstly, we recognize that CO2 consists of one carbon (C) atom and two oxygen (O) atoms. Carbon has a molar mass of around 12.01 grams per mole, and oxygen has a molar mass of about 16.00 grams per mole.
To find the total molar mass of CO2, we add the molar masses of carbon and two oxygen atoms together. This gives us approximately 44.01 grams per mole.
Next, we convert the number of atoms given to moles. This conversion utilizes Avogadro's number, which is about 6.022 x 10^23 atoms per mole. By dividing the given number of atoms by Avogadro's number, we find the number of moles, approximately 37 moles.
Finally, to find the mass in grams, we multiply the number of moles by the molar mass. This yields a result of approximately 1.63 x 10^3 grams which is approximately 1629 g.
4.
How many grams are in 3.3712 x 10^{25} atoms of CCl_{4}? (Molar mass of CCl_{4} is 153.81 g)
Correct Answer
B. 8613.36 g
Explanation
Stoichiometry (as one step):
(3.3712 x 10^25 atoms) x (1 mole/6.02 x 10^23) x (153.81g/1 mole) = answer
OR as two steps
To change from atoms to grams requires TWO steps:
1st: Change to moles: Take your atoms and DIVIDE by Avogadro’s number:
3.3712 x 10^25 divided by 6.02 x 10^23 = 56 moles
2nd: Change to grams: Take your moles and MULTIPLY by molar mass:
56 moles x 153.81 g/mol =
5.
How many grams are in 2.1672 x 10^{25} atoms of Glucose C_{6}H_{12}O_{6}?
(The molar mass of glucose is: 180 g/mol)
Correct Answer
D. 6,480 g
Explanation
To find the mass of 2.1672×10252.1672×1025 atoms of glucose (�6�12�6C6H12O6), you first calculate the number of moles using Avogadro's number. This yields approximately 36 moles. Then, using the molar mass of glucose (180 g/mol), you find the mass to be around 6480 grams.
6.
How many atoms are there in 118.082 g of Potassium?
Correct Answer
C. 1.818 x 10^24 atoms
Explanation
To change from grams to atoms requires TWO steps:
1st: change to moles: Take your grams and divide by molar mass.
118.082 g divided by 39.1 g = 3.02 moles
2nd: Change to atoms: Take your moles and multiply by Avogadro’s number:
3.02 x 6.02 x 10^23 = 1.818 x 10^24
7.
How many atoms are there in 70.554 g of Sulfur?
Correct Answer
D. 1.32 x 10^24 atoms
Explanation
To change from grams to atoms requires TWO steps:
1st: change to moles: Take your grams and divide by molar mass.
70.554 g divided by 32.07 g = 2.2 moles
2nd: Change to atoms: Take your moles and multiply by Avogadro’s number:
2.2 x 6.02 x 10^23 = 1.32 x 10^24
8.
How many atoms are there in 80.223 g of Magnesium?
Correct Answer
A. 1.99 x 10^24 atoms
Explanation
To change from grams to atoms requires TWO steps:
1st: change to moles: Take your grams and divide by molar mass.
80.223 g divided by 24.31 g = 3.3 moles
2nd: Change to atoms: Take your moles and multiply by Avogadro’s number:
3.3 x 6.02 x 10^23 = 1.99 x 10^24 atoms
9.
How many atoms are there in 18.02 g of H_{2}O? (Hint: How many atoms are the in each molecule of H_{2}O?)
Correct Answer
C. 1.8 x 10^24 atoms
Explanation
Stoichiometry:
(18.02 g Water) x (1 mole/ 18.02 g) (6.02 x 10^23 atoms/mole) x (3 atoms/1 molecule)
To change from grams to atoms requires 3 steps:
1st: change to moles: Take your grams and divide by molar mass.
18.02 g divided by 18.02 g = 1 moles
2nd: Change to atoms: Take your moles and multiply by Avogadro’s number:
1 x 6.02 x 10^23 = 6.02 x 10^23 atoms
BUT, remember that a molecule of water is made up of two hydrogen atoms and 1 oxygen atom -- so multiply by 3!
10.
How many atoms are there in 148.375 g of LiCl? (Hint: How many atoms are found in each LiCl?)(Use molar mass for LiCl = 42.394)
Correct Answer
D. 4.21 10^24 atoms
Explanation
One step:
(148.364g) x (1 mole/42.394 g) x(1mole/6.02 x 10^23) (2 atoms in each LiCl) =
(To change from grams to atoms requires Three steps:
1st: change to moles: Take your grams and divide by molar mass.
148.375 g divided by 42.394 g = 3.5 moles
2nd: Change to atoms: Take your moles and multiply by Avogadro’s number:
3.5x 6.02 x 10^23 = 2.107 x 10^24 atoms
3rd: There are two atoms in each LiCl -- so multiply by 2.