16 Questions
What is the first step in determining the chemical formula of a compound?
Find the percentage composition of each element
What is the empirical formula of a compound?
The formula that represents the lowest whole-number mole ratio of atoms
What is the next step after finding the moles of each element in determining the chemical formula?
Compare the ratio of moles to determine the ratio of atoms
What is the purpose of finding the molar mass of the empirical formula?
To compare it to the actual molar mass of the compound
What is the molecular formula of a compound?
The actual formula for the compound
How do you determine the molecular formula if the molar mass of the empirical formula is different from the actual molar mass?
Multiply all subscripts by the ratio of the molar masses
What is the purpose of determining the molecular formula of a compound?
To determine the actual formula for the compound
What is the main difference between the empirical formula and the molecular formula?
The empirical formula is the simplified formula, while the molecular formula is the actual formula
What is the number of particles in exactly one mole of a pure substance?
6.022 x 10^23
If you have 3.5 moles of gold, how many atoms of gold do you have?
2.082 x 10^24
What is the mass of one mole of pure substance?
the mass of one mole of particles in g/mol
What can the molar mass of a substance be used as?
a conversion factor
If you have 25 grams of NaCl, how many moles of NaCl is this?
0.625 mol
What is the molar mass of nitrogen dioxide?
44.02 g/mol
If you have 0.0185 moles of sodium, what is the mass of sodium in grams?
0.45 g
How many moles of silver are in 3.60 x 10^-5 g of silver?
2.10 x 10^-6 mol
Study Notes
Mole and Measurement
- A mole (mol) is a unit of measurement for the amount of a substance, used for measuring large amounts of tiny things.
- One mole of a substance contains 6.022 x 10^23 particles or atoms.
- Example: If you have 4.0 moles of helium, you have 4.0 x 6.022 x 10^23 atoms of it.
Molar Mass
- Molar mass is the mass of one mole of a pure substance, measured in g/mol.
- Molar mass is the same number as the atomic mass on the periodic table, but with a different meaning.
- Molar mass can be used as a conversion factor, and is a ratio of equivalent values.
Examples and Practice
- If you have 3.50 mol of gold, you have 3.50 x 26.98 g of gold.
- If you have 12.6 g of aluminum, you have 12.6 / 26.98 mol of aluminum.
- The mass of 0.0185 mol of sodium is 0.0185 x 22.98 g.
- 3.60 x 10^-5 g of silver is equal to 3.60 x 10^-5 / 107.87 mol of silver.
Molar Mass of Molecules
- To calculate the molar mass of a molecule, add the molar masses of its elements.
- Example: The molar mass of nitrogen dioxide is the sum of the molar masses of nitrogen and oxygen.
- If you have 25 grams of NaCl, you can calculate the moles of NaCl by dividing by the molar mass of NaCl.
- If you have 32 grams of H2S, you can calculate the moles of H2S by dividing by the molar mass of H2S.
Percent Composition and Determining Chemical Formulas
- Percent composition is the percentage of each element in a compound, based on mass.
- To determine the chemical formula of a compound, start by finding the percent composition.
- Then, find the grams of each element, calculate the moles of each element, and compare the ratio of moles to determine the ratio of atoms in the compound.
Determining Chemical Formulas
- Empirical formula: the simplest whole-number ratio of atoms in a compound.
- Molecular formula: the actual formula for the compound, which may not be the simplest whole-number ratio.
- To determine a molecular formula, find the molar mass of the empirical formula and compare it to the actual molar mass of the compound.
Learn about the mole unit of measurement, its significance in measuring large amounts of tiny things, and how to calculate the number of particles in a mole of a substance.
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