Chemistry Calcs

Question 1

Mr meaning

Answer 1

Relative formula mass

Question 2

Ar meaning

Answer 2

Relative atomic mass

Question 3

How do you calculate relative formula mass?

Answer 3

Periodic table mass number timsed by little number
Eg H= 1 O = 16
H20 = 2+16=18

Question 4

How do you calculate RAM? (Ar)

Answer 4

Multiply percentage abundance by isotope mass number
Divided by 100

Question 5

What is an isotope?

Answer 5

Different forms of the same element with the same amount of protons but different neutrons

Question 6

Mass, moles and RAM equation

Answer 6

Mass = moles x RAM/RFM

Question 7

What is avogadros number and what’s it used for?

Answer 7

6.0221x10 (power of 23)
- the amount of molecules in a mole

Question 8

Definition of moles

Answer 8

A mole is the number of atoms in exactly 12g of carbon 12 (mol)

Question 9

Mass of one mole of a substance is equal to

Answer 9

The relative atomic mass of formula mass

Question 10

What is ionic bonding?

Answer 10

The electrostatic attraction between oppositely charged ions

Question 11

1:2 ratio meaning

Answer 11

There is twice as much of the second compound/element to make up the other. =multiply by 2

Question 12

What is a limiting reactant?

Answer 12

-first reactant to be fully used up
- brings reaction to an end

Question 13

How can you ensure all the reactant has reacted in the reaction after it has stopped?

Answer 13

Add more excess reactant to see if the reaction continues

Question 14

Percentage yield equation

Answer 14

Actual yield/g divided by theoretical yield /g multiplied by 100

Question 15

Why is the theoretical yield bigger than the actual

Answer 15

If it’s a reversible reaction, loss of products (eg gasses)

Question 16

Atom economy equation

Answer 16

Mass of useful products / mass of all products multiplied by 100
=?%

Question 17

Why is atom economy important?

Answer 17

Minimise energy and recourse cost, reduce pollution due to waste gasses, expensive recourses, raw materials are scarce so should be conserved

Question 18

If there are more by-products in a reaction is atom economy high or low

Answer 18

Lower if more waste products

Question 19

How can you increase atom economy?

Answer 19

Find a purpose/use for the products

Question 20

How do you calculate concentration from volume (v) moles (n)

Answer 20

n=cV
Moles = conc x volume

Question 21

What is conversion dm3 to cm3

Answer 21

X1000

Question 22

What is concentration measured in?

Answer 22

mol/dm3

Question 23

What is volume measured in?

Answer 23

dm3 or cm3

Question 24

Nitric acid formula

Answer 24

HNO3

Question 25

Sulphuric acid formuka

Answer 25

H2SO4

Question 26

Sodium sulphate formula

Answer 26

Na2SO4

Question 27

Phosphoric acid formula

Answer 27

H3PO4

Question 28

Sodium hydroxide

Answer 28

NaOH

Question 29

What is the purpose of a titration

Answer 29

To determine volume of solution needed to reach an endpoint eg colour change due to ph from phenolphthalein indicator

Question 30

Increased concentration means higher or lower ph

Answer 30

Lower as it becomes a stronger acid =further from neutral 7

Question 31

Decreased concentration effect on ph

Answer 31

Increase ph means weaker acid = closer to neutral 7

Question 32

How do you mark an endpoint of a titration

Answer 32

Using indicator solution. When colour changes = endpoint.

Question 33

Avogadros law in terms of gasses

Answer 33

Equal volumes of gases at the same temp and pressure contain the same number of molecules should be volume 24dm3

Question 33

Avogadros law in terms of gasses

Answer 33

Equal volumes of gases at the same temp and pressure contain the same number of molecules should be volume 24dm3

Question 34

Gas volumes equation

Answer 34

Volume (dm3) = mol x 24

Question 35

Percentage composition equation

Answer 35

= RAM x no. Atoms of element needed / rfm of whole compound x 100

Question 36

Why is percentage yield not always 100%

Answer 36

Some product may be lost when separated from reactant mixture Reversible reactions Some reactants may react differently into other products