S1 -Chemical formulae & chemical equations

Question 1

What can a chemical reaction be described as?

Answer 1

The process of going from reactants to products in a reaction

Question 2

What can you write to show these chemical reactions?

Answer 2

Word and symbol equations

Question 3

What do state symbols show? and list the four main ones

Answer 3

They show the physical state the reactants and products are in

(s) Solid
(l) Liquid
(g) Gas
(aq) Aqueous - dissolved in water

Question 4

What do symbol equations always need to be?

Answer 4

Balanced - there must be the same number of atoms on both side

Question 5

What method should you take for balancing equations?

Answer 5

Balance just one atom at a time - and do it in pencil

Question 6

What is the empirical formula?

Answer 6

The simplest formula that tells you the ratio of different elements in a compound

Question 7

What are the simple steps for working out the empirical formula?

Answer 7

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

Question 8

What is the molecular formula?

Answer 8

Tells you the actual number of atoms of each element in a single molecule

Question 9

What is the method for working out the molecular formula?

Answer 9

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

Question 10

What are the three steps for working out masses in reactions?

Answer 10

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

Question 11

What is a percentage yield?

Answer 11

The amount of product obtained in a chemical reaction - the more reactant you start off with the higher the yield

Question 13

How is the theoretical yield of a reaction calculated?

Answer 13

From the balanced equation when calculating masses in reactions

Question 14

What is a percentage yield always between?

Answer 14

0-100%

Question 15

What does a 100% yield mean?

Answer 15

You got all the products you expected to get

Question 16

What does a 0% yield mean?

Answer 16

No reactants were converted into product - no product was made

Question 17

What two things can salts be?

Answer 17

Anhydrous or hydrated

Question 18

What do all salts consist of?

Answer 18

A lattice of positive and negative ions - some have eater molecules incorporated in the lattice too

Question 19

What is the water in a lattice called?

Answer 19

Water of crystallisation

Question 20

A solid salt containing water of crystallisation is….

Answer 20

Hydrated

Question 21

If a solid doesn’t contain any water of crystallisation it is…

Answer 21

Anhydrous

Question 22

How can you calculate how much water crystallisation a salt contains?

Answer 22

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)

Question 23

What happens to many hydrated salts when they are heated?

Answer 23

They lose their water of crystallisation and become anhydrous

Question 24

What do you need to know to work out the formula of how much water of crystallisation a salt contains?

Answer 24

Mass of the salt when hydrated and anhydrous

Question 25

What are the five steps for working out how much water crystallisation a salt contains?

Answer 25

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

Question 26

How do you work out percentage yield?

Answer 26

Percentage yield = actual yield (grams)/theoretical yield (grams)