Mole Calculations Flashcards
Percentage Composition:
What is the formula for actual % by mass?
% by mass = Mass of Element / Mass of whole sample
Percentage Composition:
What is the formula for theoretical % by mass?
Theoretical % by mass = (Ar of element x number of elements) / Mr of compound
What is a mole? What does it contain?
A mole is a unit of measurement which describes the amount of substance.
A mole contains 6.02 x 10^23 particles, also known as Avogadro’s Constant.
How to derive the number of moles from Avogadro’s Constant?
Number of Moles = Number of particles / Avogadro’s Constant (6.02x10^23)
How does one derive the number of moles from mass and molar mass?
Number of Moles = Mass (g) /Molar mass (g/mol)
What is the formula for converting between the number of moles and the molar volume?
Number of Moles = Volume of Gas / Molar Volume.
At room temperature and pressure, one mole of gas occupies 24.0 dm^3. Hence, take molar volume to be 24dm^3.
What is the formula involving number of moles and concentration? What is the formula for molar concentration?
Take into account molar concentration SI Unit: mol/dm^3. Hence,
molar concentration = Number of moles/volume
What is the formula involving mass and concentration? what is the formula for mass concentration?
mass concentration = mass(g) / volume (dm^3)
What is Molecular Formula? What is Empirical Formula? What is the relation between them?
Molecular formula shows the number of atoms in 1 molecule of a substance/
Empirical formula shows the simplest ratio of the atoms of different elements present.
Molecular formula = n(Empirical formula)
n = Molecular formula/Empirical Formula
What are the steps for calculating empirical formula?
1) Write down the mass of each element
2) Write down the molar mass of each element
3) find the number of moles of each element
4) Divide all by the smallest no. of moles
5) Express the relative amounts as a simplest ratio.
What are limiting and excess reactants?
A limiting reactant is the reactant that is used up first in a reaction.
An excess reactant is one that is not completely used up during the reaction.
Which reactant is used in stoichiometric calculations —- limiting reactant or excess reactant
The limiting reactant is used during stoichiometric calculations.
What is percentage yield, and what is its formula?
Percentage yield = actual yield / theoretical yield x 100%
Theoretical yield is the calculated amount of products that could be obtained when the reaction is completed.
Actual yield is the amount of pure products that is actually produced when the reaction is completed.
Why is theoretical yield always greater than actual yield?
1). Impure reactants
2). reversible reactions that the reactions do not proceed 100% from left to right
3). human errors / procedural errors
What is the formula for percentage purity?
Percentage purity = mass of pure substance / mass of sample x100%
