Calculations Flashcards
Define empirical formula
The most simple ratio of atoms of an element in a compound
Define molecular formula
The actual number of atoms of an element in a compound
How do you calculate the empirical formula?
M ass
R elative atomic mass
D ivide the mass of each element by the relative atomic mass
DS divide by smallest of two to find simplest ratio
F ormula
How do you calculate the molecular formula?
- Find empirical formula mass
- Divide the relative formula mass by the empirical formula mass
- Answer shows how many times larger the molecular formula is than the empirical formula
How is the Avogadro constant written in standard form
6.02 x 10^23
What is the formula to calculate the mass in (g) of an atom
mass (g) = number of MOLES x relative mass (Mr)
Calculation for the number of moles in a sample
number of moles (n) = mass (g) ÷ Mr (relative mass from periodic table)
How do you calculate the number of particles/molecules/atoms in a sample
(N) = number of moles (n) x Av (6.02x 10^23)
What is the law of conservation of mass
Total mass of reactants = Total mass of products
How do you calculate the masses of reactants and products
- Calculate the Mr of the reactant and the product ONLY THE ONES MENTIONED IN THE QUESTION
- decide wether they are asking for the MASS OF PRODUCT or REACTANT
- IF REACTANT : Mr of reactant ÷ Mr of product
- IF PRODUCT : Mr of product ÷ Mr of reactant
- Multiply by known mass in question
What does the ‘limiting reactant’ mean
The reactant with the smaller amount of moles and will determine how much product will be made
What does the reactant ‘in excess’ mean
The larger reactant
How do you deduce a balanced equation for a reaction (STOICHIOMETRY)
- Calculate the number of moles for each element
- Divide each answer by the smaller amount of the two
- Find the simplest whole number ratio
Concentration in gdm^-3 =
Mass of solute (g) ÷ volume of solution (dm^3)
Percentage yield =
Actual yield
———————— x 100
theoretical yield
