Quantitative Chemistry Flashcards
How to calculate the percentage by mass of an element in a compound? (%)
=Ar x number of atoms of that element / Mr of the compound X 100
What is one mole of an atom?
It will have a mass in grams that is equal to its relative formula mass
How do you calculate the number of moles? (mol)
=mass in g / Mr of element or compound
What does it mean if mass is conserved?
It is where there are the same number and types of atoms on each side of a reaction equation
Why might the mass of a substance increase?
Because one of the reactants is a gas and before the reaction, the gas is already floating around in the air
Why might the mass of a substance decrease?
Because one of the products is a gas and if the reaction vessel isn’t enclosed, the gas may escape as it is formed
Why does a reaction stop?
Because one of the reactants is all used up and any other reactants are in excess (usually added on excess to make sure other reactant is used up)
What is the limiting reactant?
The reactant that is used up in a reaction because it limits the amount of product formed (they are directly proportional)
How do you calculate the volume of a gas? (dm3)
=mass of gas (g) / Mr of gas X 24
How do you calculate the concentration of a solution? (g/dm3)
=mass of solute (g) / volume of solvent (dm3)
How do you work out the concentration in mol/dm3?
=no of moles of solute (mol) / volume of solvent (dm3)
How do you calculate the atom economy?
=relative formula mass of desire product / relative formula mass of all reactants X 100
What is the atom economy?
Tells you how much of the mass of the reactants is wasted when manufacturing a chemical and how much ends up as the desired product
What is meant by 100% atom economy?
Means that ALL the atoms in the reactants have been turned into the desire product.the higher the atom economy the ‘greener’ the process
How do you calculate the percentage yield?
=mass of product made / maximum theoretical mass of product X 100
