Amount Of Substances

Question 1

What is the definition of a mole (amount of substance)?

Answer 1

The amount of any substance containing as many particles as there are carbon atoms in exactly 12g of the carbon 12 isotope

Question 2

What is the number of particles per mole called?

Answer 2

Avogadros constant (6.02 x10 23)

Question 3

How do you calculate molar mass?

Answer 3

Sum of mass number (same as relative formula mass)
gmol ^ -1

Question 4

What is the formula for amount of substance using mass and molar mass (mr)?

Answer 4

Amount of substance= mass in g / molar mass
n= m/mr

Question 5

How do you calculate the number of particles present in a substance using avogadros and moles of particle?

Answer 5

Number of particles= moles of particles x avogadros constant

Question 6

What is empirical formula?

Answer 6

The simplest whole number ratio of atoms of each element present in a compound

Question 7

How do you find the empirical formula?

Answer 7

Divide % by mass/ relative atomic mass to find the number of moles. Then divide all by the smallest mole to get a ratio then make the formula.

Question 8

What is molecular formula?

Answer 8

The actual number of atoms of each element present in a compound

Question 9

What do you need in order to find the molecular formula?

Answer 9

The empirical formula and the relative molecular mass

Question 10

What is hydrated?

Answer 10

A crystalline compound which contains water molecules in its structure.

Question 11

What is anhydrous?

Answer 11

A compound when all the water of crystallisation has been removed.

Question 12

What is water of crystallisation ?

Answer 12

Water molecules that form an essential part of the crystalline structure of a compound

Question 13

What are the 2 assumptions which must be made about water pf crystallisation?

Answer 13

1) all of the water has been lost (good solution is to heat to constant mass, repeatingly heat the crystals until there is no further loss of mass.)
2) no further decomposition (some salts start to decompose further if heated very strongly.)

Question 14

Why might % yield not be 100%?

Answer 14

-reaction may be at equilibrium and may not be completion.
- other side reactions may take place leading to by products
- reactants may not be pure.
- some of reactants or products may be left in apparatus used in experiment.

Question 15

How can we improve atom economy?

Answer 15

Finding uses for any waste products so its more sustainable. E.g. CO2 could use in fizzy drinks industry.

Question 16

What atom economy would an addition reaction have and why?

Answer 16

100% atom economy as it has no by products.