topic 3 -quantitive chemistry Flashcards
what is the equation for calculating the percentage mass of an element in a compound?
percentage mass of an element in a compound = (Ar x number of atoms of that element/ Mr of the compound ) X 100
what is avogadro’s constant?
6.02 x 10^23
what is the formula that links mole mass and MR
mass = MR . (x) mole
why might the mass of the products be higher than the mass of the reactants
one of the reactants is a gas and the products are solid.
before the reactin, the gas is floating and not contained in the reaction vessel therefore you cannot account for its mass.
when the gas reacts to form part of the product, it becomes contained iside the reaction vessel so the total mass of the stuff inside the reaction vessel increases
why might the mass of the products be lower than the mass of the reactants?
one of the products is a gas
before the reaction all the reactants are contained in the reaction vessel.
if the vessel isnt enclosed, then the gas can escape from the reaction vessel as it is formed.
it is no longer contained in the reaction vessel so you cant account its mass
the total mass of the stuff inside the reaction essel decreases
if you know the masses of the reactants and products that took part in a reaction, how can yuo work out the balanced symbol equation?
work out the mr for each substance
divice the mass of each substance by its mr to calculate how many moles od each substance was reacted or produced
divide by the smallest numer of moles
what is a limiting reactant?
the reactant that is used up in a reaction
( because it limits the amount of product that is formed)
describe the relationship between the product formed and the limitign factor.
the amount of product formed is directly proportional to the amount of limiting factor
write the steps oto calculate the mass of alluminium oxide formed when 135g of aluminium is burned in air.
write out the balanced equation
4 al + 3 02 -> 2Al203
calculate the relativ formula mass Al ; 27 Al203 ; (2x27) +(3x16) = 102
calculate the number of moles of aluminium in 135g ; moles = mass/mr = 135/27 = 5
look at the ration of moles in the equation 4 moles of al react to produce 2 moles of al203 - half thenumber of moles are produced, so 5 moles of al will react to produce 2.5 moles of al203
calculate the mass of 2.5 moles of aluminium oxide - mass = moles x mr = 2.5 x 102 = 255g
what is the formula to find the volume of a gas?
volume of gas = mass of gas / mr of gas x 24
what is concentration?
the amount of a substance in a certain volume
what is concentration?
the amount of a substance in a certain volume
is more solute , more or less concentrated?
more concentrated
what is the equation that links concentration, mass of solute and volume of solvent?
concentration = mass of solute/volume of solvent
what is the equation that links number of moles , concentration and volume?
number of moles= concentration x volume
