S1 -Chemical formulae & chemical equations Flashcards
What can a chemical reaction be described as?
The process of going from reactants to products in a reaction
What can you write to show these chemical reactions?
Word and symbol equations
What do state symbols show? and list the four main ones
They show the physical state the reactants and products are in
(s) Solid
(l) Liquid
(g) Gas
(aq) Aqueous - dissolved in water
What do symbol equations always need to be?
Balanced - there must be the same number of atoms on both side
What method should you take for balancing equations?
Balance just one atom at a time - and do it in pencil
What is the empirical formula?
The simplest formula that tells you the ratio of different elements in a compound
What are the simple steps for working out the empirical formula?
1) List all the elements in the compound
2) Underneath write the given masses/percentages
3) Divide each mass by their Ar
4) Turn them into a simple ratio by either x/÷
5) Put ratio into simplest form
What is the molecular formula?
Tells you the actual number of atoms of each element in a single molecule
What is the method for working out the molecular formula?
1) Find the mass of the empirical formula
2) Divide the relative molecular mass by the total mass from 1)
3) Use the answer in the 2) to times it by the empirical formula
What are the three steps for working out masses in reactions?
1) Write out a balanced equation
2) For the two bits you want, work out relative formula (Mr) and multiply them by balancing numbers in the equation
3) Apply the rule: divide to get one, multiply to get all
What is a percentage yield?
The amount of product obtained in a chemical reaction - the more reactant you start off with the higher the yield
How is the theoretical yield of a reaction calculated?
From the balanced equation when calculating masses in reactions
What is a percentage yield always between?
0-100%
What does a 100% yield mean?
You got all the products you expected to get
What does a 0% yield mean?
No reactants were converted into product - no product was made
What two things can salts be?
Anhydrous or hydrated
What do all salts consist of?
A lattice of positive and negative ions - some have eater molecules incorporated in the lattice too
What is the water in a lattice called?
Water of crystallisation
A solid salt containing water of crystallisation is….
Hydrated
If a solid doesn’t contain any water of crystallisation it is…
Anhydrous
How can you calculate how much water crystallisation a salt contains?
Use the formula provided in the question - one mole of a hydrated salt always has a particular number of moles of water crystallisation (always a whole number)
What happens to many hydrated salts when they are heated?
They lose their water of crystallisation and become anhydrous
What do you need to know to work out the formula of how much water of crystallisation a salt contains?
Mass of the salt when hydrated and anhydrous
What are the five steps for working out how much water crystallisation a salt contains?
1) Work out the mass of the hydrated and anhydrous salts
2) Find the number of moles of water lost
3) Find the number of moles of the anhydrous salt
4) Work out the ratio of moles of anhydrous salt : moles of water
5) Either round off number or add back into equation
How do you work out percentage yield?
Percentage yield = actual yield (grams)/theoretical yield (grams)
