2.1 formulas

Question 1

What is the empirical formula?

Answer 1

The simplest whole number ratio of elements in a compound

Question 2

How do you calculate the empirical formula (from grams composition)?

Answer 2

1) Divide each amount (of grams) by its atomic mass)
2) Divide each of these answers by whichever answer is the smallest
3) Find the lowest WHOLE NUMBER ratio

Question 3

What is the formula for amount of substance(moles)

Answer 3

n = mass DIVIDED by Mr

Question 4

What is the formula for mass?

Answer 4

Mass = Moles x Molar mass

Question 5

What is the formula for Mr given moles and molar mass?

Answer 5

Mr = mass DIVIDED by moles

Question 6

What is the formula for number of particles?

Answer 6

Number of particles = Number of moles x Avogadro’s constant

Question 7

What value is given to Avogadro’s constant

Answer 7

6.02 x 10 to the power of 23

Question 8

What is the formula for moles given avogadro’s constant and the number of particles?

Answer 8

n = Number of particles DIVIDED by avogadro’s constant

Question 9

What is the ideal gas equation?

Answer 9

pV=nRT

Where p = pressure 
V = Volume
n = Number of moles
R = Gas constant (given on the data sheet - 8.314)
T = Temperature

Question 10

How can you calculate pressure using the ideal gas equation?

Answer 10

p = (nRT) DIVIDED by volume

Question 11

How can you calculate volume using the ideal gas equation?

Answer 11

V = (nRT) DIVIDED pressure

Question 12

How can you calculate moles using the ideal gas equation?

Answer 12

n = (pV) DIVIDED by (RT)

Question 13

How can you calculate temperature using the ideal gas equation?

Answer 13

T = (pV) / (nR)

Question 14

What is the gas volume equation?

Answer 14

V(dm^3) = n x 24
V (cm^3) = n x 24000

This formula is used when working out gas volume at RTP(Room temperature and pressure)

Question 15

How to work out the proton number of an element?

Answer 15

Look at it’s atomic number (smaller number on periodic table)

Question 16

How to work out the number of neutrons in an element

Answer 16

Relative atomic mass - atomic number

Question 17

How do you work out the relative atomic mass?

Answer 17

Multiply each isotopic mass by percentage abundance, add the results together and divide by 100

Question 18

How do you work out the RFM of a compound?

Answer 18

Add all the relative atomic masses together

Question 19

How do you work out an ionic compound’s formula

Answer 19

Balance the positive and negative charges

e.g Mg0 or CaF2

Question 20

What is the formula for atom economy?

Answer 20

(Mass of desired product) / (Total mass of product) x 100

Question 21

How do you work out the atom economy?

Answer 21

1) Identify the useful product
2) Work out the Mr of all the products
3) Use the formula to calculate the atom economy

Question 22

What is the formula for percentage yield?

Answer 22

[Actual yield (in moles)] / [Theoretical yield (in moles)] x 100

Question 23

How do you work out the percentage yield?

Answer 23

1) Write a balanced equation
2) Work out the mole ratio
3) Find the theoretical yield
4) Input numbers into the percentage yield and calculate
5) ALWAYS remember the units is %

Question 24

How do you work out the water of crystallisation?

Answer 24

Using the dot formula

Question 25

How do you work out the water of crystallisation? (steps)

Answer 25

1) Work out the anhydrous mass
2) Calculate the amount, in mol, of anhydrous salt
3) Calculate the mass of water
4) Calculate the amount,in mol, of water
5) Determine the formula of the hydrate salt using the molar value. (divide the mass of water by the Mr of water)

Question 26

What is the formula for concentration?

Answer 26

C = n/V

Question 27

What is the formula for volume?

Answer 27

V = n/C

Question 28

What is the formula for moles, given concentration and volume?

Answer 28

n = C x V