Amount of substance

Question 1

What are the definitions of hydrated and anhydrous?

Answer 1

Hydrated = a crystalline compound that contains water molecules

Anhydrous = a substance that contains no water molecules

Question 2

What is the definition of water of crystallisation?

Answer 2

Water molecules that form an essential part of the crystalline structure

Question 3

How do you calculate no. moles of water of crystallisation in a hydrated salt?

Answer 3

anhydrous H2O
mass

moles

ratio 1 : x

Question 4

How do you write a dot formula of hydrated salts?

Answer 4

E.g. MgCl2H10O5 = MgCl2.5H2O

Question 5

Why is a hydrated salt heated multiple times?

Answer 5

If it is heated to a constant mass then you can ensure that all of the water of crystallisation has been removed

Question 6

What is the definition of an empirical formula?

Answer 6

The simplest whole number ratio of atoms in a compound

Question 7

What is the definition of a molecular formula?

Answer 7

The actual number of atoms of an element in a compound

Question 8

How do you calculate empirical formula?

Answer 8

With the mass, moles, ratio, E.F table

e.g. Mg N

mass 72/24.3 28/14

Question 9

How do you calculate molecular formula from an empirical formula?

Answer 9

1. Find the multiplication factor (n) between empirical and molecular
2. Multiply empirical by multiplication factor

n = Mr of molecular (given) / Mr of empirical (calculated)

Question 10

How would not putting the lid back onto the crucible while cooling affect the no. moles of water of crystallisation?

Answer 10

More water molecules from the air would condense back into the crucible so the mass of water LOST would decrease

mass (water lost) –> less
moles –> less
x –> lower

Question 11

What is the equation for percentage uncertainty?

Answer 11

% uncertainty = (no. readings x uncertainty of equipment / quantity) x 100

Question 12

What is the formula for calculating no. particles?

Answer 12

particles = moles × NA (Avogadro’s constant)

Question 13

What is the ideal gas equation?

Answer 13

pV = nRT

p = pressure, Pa
V = volume, m3
n = moles
R = 8.314
T = temperature, K

Question 14

What are the unit conversions you need to know for the ideal gas equation?

Answer 14

kPa /1000 = Pa
cm3 / 1000000 = m3
dm3 / 1000 = m3
°C + 273 = K

Question 15

What is the formula triangle which links moles, mass and Mr?

Answer 15

mass

moles Mr

Question 16

What is the formula triangle which links moles and volume of gas at ROOM TEMPERATURE?

Answer 16

volume
moles 24dm3
24000cm3

Question 17

How do you calculate no. molecules and no. atoms?

Answer 17

no. molecules = moles x NA

no. atoms = moles × no. atoms in molecule x NA

Question 18

What is Avogadro’s constant?

Answer 18

6.02 x 10^23

Question 19

What is the formula triangle for moles in SOLUTION?

Answer 19

moles

concentration volume

Question 20

What is a standard solution?

Answer 20

A solution with a known concentration