Chemical equations Flashcards
what is percentage composition by mass?
Tells you how much is a compound is made up of a particular element.
Formula for working out percentage composition by mass?
(atomic mass of one element/formula mass of the compound) x 100
What is a mole?
an animal
hahaha I’m so funny
its a chemical quantity for the weight of atoms.
one mole of carbon ways 12g and one mole of a compound weighs the same as the formula mass
How do you work out the number of moles?
Moles = mass/formula mass
remember the triangle with mass on top, moles to the left and formula mass to the right.
What is empirical formula?
a formula giving the ratio of the elements present in a compound
How do you calculate empirical formula?
1) find the mass of each element-will be given in test
2) dive that mass by the atomic mass of that element
3) find the ratio of these numbers by dividing by the smallest number
4) but the compound into the ration e.g
sulphur : oxygen
1 : 2
so2
How do you work out the reacting mass?
This is used to see how much of a product will be made in a reaction.
1) find the formula mass of all elements in the equation
2) arrange the numbers (grams) into that equation.
with this you would be able to see how many grams will be produced from a reaction.
What is percentage yield?
A measure of how effectively the starting materials in a reaction are converted into the desired product as a percentage.
How do you work out percentage yield?
(mass of product you made/theoretical mass of product which you should have got) x 100
how to use scale factors in reacting masses.
1) decide if you are scaling up the mass or down
2) if scaling up divide the mass that will be scaled up too by the original amount. e.g 1000/48.
2b) if scaling down do the same but the other way around e.g 48/1000
3) times that answer by what the mass of the final product would have been if you didn’t scale up/down.
4) that’s the answer in grams E.g. 1666g
How you work out average ram (relative atomic mass) of a the isotopes of an element?
(,mass no. of isotope 1 x amount of that isotope) + (mass no. of isotope 2 x amount of that isotope)
the amount of that isotope will be a decimal percentage
What is the formula for working out atom economy?
(total Mr of useful products)/(total Mr of reactants) x 100
Mr = formula mass
Formula for working out concentration of an solution?
amount dissolved (g) / volume of solution (dm3)
if you are given volume in cm3 then divide that volume by 1000 to get it into dm3
How do you work out the number of atoms in a mass of an element?
Avogadro’s constant x no. moles
How to work out rate of reaction?
volume produced/time
