Chapter 3: Calculations with Chemical Formulas and Equations. Flashcards
What is molecular mass?
The sum of the atomic masses of all the atoms in a molecule of the substance. It is therefore also the average mass of a molecule of that substance, expressed in atomic mass units.
EXP: H20 (2 x 1.0 amu for Hydrogen + 16.0 amu for O = 18.0 amu
What is the formula mass of a substance?
The formula mass of a substance is the sum of the atomic masses of all atoms in a formula unit of the compound.
EXP: Sodium Chloride (NaCl) has a formula mass of 58.44 amu (22.99 amu from Na + 35.45 amu from Cl)
What is a mole?
The quantity of a given substance that contains as many molecules or formula units as the number of atoms in exactly 12g of carbon-12.
The number of atoms in a 12-g sample of carbon-12 is called Avogadro’s number (6.0221367 x 10^23)
A mole of a substance contains Avogrado’s number of molecules.
What does the term mole mean for ionic substances?
The number of formula units of the substance. EXP: A mole of sodium carbonate Na2CO3 is a quantity containing 6.02 x 10^23 NaCO3 units.
What is the molar mass?
The molar mass of a substance is the mass of one mole of the substance.
What is the percentage composition?
The mass percentages of each element in the compound. You can then determine the formula from this percentage composition.
- If this compound is a molecular substance, you must find the molecular mass of the compound.
What is the mass percentage of “A”?
The parts of “A” per hundred parts of the total, by mass.
Mass percentage of “A” is the number of grams of “A’ n 100g of the whole.
What is the empirical formula?
The formula of a substance written with the smallest integer subscripts.
What is the relationship between the molecular formula and the empirical formula.
The molecular formula is the multiple of the empirical formula. For example. C2H2 is just (CH)2.
For any molecular compound:
Molecular mass = n x (Empirical formula mass)
“n” is the number of empirical formula units.
What is the molecular formula?
First you need to multiple the subscripts of the empirical formula by “n” - which can then be calculated n = molecular mass / empirical formula mass.
Once you determine the empirical formual for a compound, you can calculate its empirical formula mass.
What is the limiting reactant?
The reactant that is entirely consumed when a reaction goes to completion
How are the moles of a product determined?
By the starting moles f limiting reactant
