Section 3 - Equations, calculations and electrolysis Flashcards
How do you work out Mr value (Relative formula mass)
The Ar of the atoms added together
What is a mole?
6.02x10^23 (602 000 000 000 000 000 000 000)
Define the molar mass
The mass of one mole
What is the formula for working out the number of moles?
Mass/Mr
What is the formula for working out the mass of an element of compound?
Number of moles x Mr
What is the formula for working out the Mr?
Mass/Number of moles
What is the method to calculating the amount of product from a mass of reactant?
1) Write a balanced equation
2) Work out relative formula masses (Mr) of the reactant and product
3) Find out how many moles there are of substances you know the mass of
4) Used the balanced equation to work out how many moles there’ll be of the other substance
5) Use the number of moles to calculate the mass
What is the empirical formula?
The smallest whole number ratio of atoms in a compound
How do you work out empirical formula?
1) List all of the elements in the compounds
2) Write down their masses
3) Find the number of moles by dividing each mass by the relative atomic mass for that element
4) Turn these numbers into a ratio by dividing by the smallest number of moles
5) Get the ratio in its simplest whole number form
How do you work out the molecular formula from the empirical formula?
1) Find the mass of the empirical formula
2) Divide the relative molecular mass of the molecular formula by the mass of the empirical formula
3) Multiply each atom of the element by that number
How do you work out the mass of a product formed?
1) Write out the balanced equation
2) Work out the Mr of the reactant and product
3) Find out how many moles there are of the substance you know the mass of
4) Use the balanced equation to work out the moles of the other substance
5) Use the number of moles to calculate the mass
How do you work out percentage yield?
Actual yield (Grams) / theoretical yield (grams) x 100
How do you work out the empirical formula using combustion? (Practical)
1) Get a crucible and heat until it’s red hot to ensure it is clean and there are no traces of oil and water
2) Leave the crucible to cool and weigh it along with the lid
3) Add some clean magnesium ribbon to the crucible and reweigh it with the magnesium in it
(The mass of magnesium is this reading minus the initial reading with the crucible and the lid on)
4) Heat the crucible and put the lid on but leave a small gap to allow it to oxidise
5) Heat strongly for 10 minutes until all of the magnesium has turned white
6) Allow the crucible to cool and reweigh the crucible with the lid and its contents
(The mass of the MgO is this reading minus the initial reading for the mass of the crucible and the lid)
How do you work out empirical formula using reduction? (practical)
1) Place a rubber bung into a test tube with a small hole in the end
2) Take the bung out the test tube and spread out a small amount of copper(ii) oxide in the middle of the tube
3) Re-insert the bung and weigh the test tube again
4) Expel the air from the test tube by gently turning on the gas after 5 seconds. Light the gas using a burning splint
5) Use a bunsen burner to heat the copper(ii) oxide for 10 minutes (or until the solid changes from black to brownish-pink)
6) Turn off the test tube and allow to cool
7) Once the tube has cooled, turn off the gas and weight the test tube with the bung and its contents
Define water of crystalisation
The water contained in a lattice
