Chapter 5: Unit 6. Conversion between Mass of a Substance and Moles
Conversion between Mass of a Substance and Moles
The molar mass is used as a conversion factor to determine how many grams are contained in a given number of moles of a substance. Similarly, the molar mass is used to determine how many moles of a substance are contained in a given number of grams.
Watch the following video:
Example#1: How many mols are present in 24.02 g of Carbon?
Since it is grams to mol conversion, molar mass is the conversion factor.
According to Periodic table molar mass of C= 12.01 g/mol
24.02 g C * 1 mol C = 2.00mols of C
12.01 g C
Example#2: How many mols are present in 54.1 g of Carbon?
Since it is grams to mols, molar mass is the conversion factor.
Molar mass of H2O= 1.008 + 2* 16.00= 18.02 g/mol
54.1 g H2O * 1mol H2O =3.00 mols of H2O
18.02 g H2O
Example #3: How many grams are in 3.57 mols of CO2?
Since it is mols to grams, molar mass is the conversion factor.
Molar mass of CO2= 12.01 + (4*16.00)= 44.01 g/mol
3.57 mols of CO2 * 44.01 1g CO2 = 157 g of CO2
1 mol CO2
Example#4 : How many atoms are present in 35.0 g of Cu?
We will use both conversion factor, molar mass and avogadro’s number to solve this problem.
Pathway:
35.0 g Cu * 1mol Cu * 6.022 *1023 atoms Cu = 3.32 *1023 atoms of Cu
63.5 g Cu 1 mol Cu
Questions:
- How many mols of H2O are in 75.0 g of H2O?
- How many grams are in 3.46 mols of NaCl?
| 3. How many molecules are present in one mole of glucose, C6H12O6? |
| 4. You have a sample of 3.01 × 1023 atoms of silver. How much does this sample weigh? |
| 5. A typical deposit of cholesterol, C27H46O, in an artery has a mass of 3.90 mg. How many molecules of cholesterol are present in this deposit? |
Ans: 1. 4.16 mols H2O
2. 202.2g NaCl
3. 6.02 * 1023
4. 53.9 g Ag
5. 6.10 *1018 molecules
Relationship Involving the Mole Concept
Avogadro’s Number
The number of Particles in 1 mole
1 mole of particle is equal to 6.02*10^23 particles
Molar MAss
The mass of a mole
mass in grams, numerically equal to a substance’s formula mass
1 mol O atom=16.0g
1 mol O2 molecules=32.0g
1 mol O3 molecules=48.0g
1 mol H2O molecules =18.0g
Molar ratio
Chemical Formulas
The numerical subscripts in a chemical formula give the number of moles of atoms of the various elements present in 1 mole of the substance
| N2 H4 | ||
| ↓ | ↓ | |
| 3mole | 2mole | 1mole |
chemical Equations
coefficient in a chemical equation give the fixed molar ratios between reactance and products in a chemical reaction for the reaction
| 2Al+3S→ Al2S3 | ||
| ↑ | ↑ | |
| 1mole | 2mole | 4mole |
| and | 2mole | 4moles |
| 1mole | N atom | H atom |