2.1.3: Amount of substance

Question 1

What are the units for amount of substance ?

Answer 1

mol

Question 2

Convert 1m3 into dm3

Answer 2

1 m3 = 1000 dm3

Question 3

Convert m3 to cm3

Answer 3

x1,000,000

Question 4

Convert Litres to dm3

Answer 4

1L = 1 dm3

Question 5

What are standard conditions ?

Answer 5

1atm and 298K

Question 6

Give equation to work out the number of particles

Answer 6

Avogadro’s number x number of moles

Question 7

Give the ideal gas equation and its units

Answer 7

PV = nRT

Pressure (Pa)
Volume (m3)
Temperature (K)
Gas constant = 8.314 ( JK-1mol)

Question 8

How do you convert degrees into kelvin ?

Answer 8

+ 273

Question 9

Give the heating method to determine water of crystallization

Answer 9

• Weigh empty boiling tube using a balance
• Place several spatulas of hydrated compound into boiling tube
• Weigh boiling tube
• Determine mass of a compound added
• Heat boiling tube over bunsen burner to drive off w.o.c as steam
• Weigh boiling tube to determine mass of anhydrous compound
• Use mass of hydrous and anhydrous compound to determine water mass
• Calculate moles of anhydrous and water
• Calculate ration between numbers to find w.o.c

Question 10

How do you convert from mol/dm3 to g/dm3

Answer 10

x by RFM

Question 11

What are 3 factors that can affect yield ?

Answer 11

• If reaction is at equilibrium it may not go to completion
• Reactants may not be pure so separation and purification may result in some product loss
• Other side reaction may occur leading to by products

Question 12

What is the atom economy if there is 1 product ?

Answer 12

100%

Question 13

What might have happened if there is a high yield but low atom economy ?

Answer 13

• One reaction may be reversible
• More products so more waste in one reaction

Question 14

What are preferable processes for reactions ?

Answer 14

• Single step so less time
• Less waste and less hazardous waste

Question 15

Define the term hydrous

Answer 15

A crystalline compound containing water molecules

Question 16

Define mole

Answer 16

The expression of the amount of substance containing 6.02 x 10^23 particles

Question 17

Define the term anhydrous

Answer 17

A crystalline compound containing no water molecules

Question 18

Define water of crystallization

Answer 18

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

Question 19

Explain amount of substance

Answer 19

Name given when counting the number of particles in a substance in mol

Question 20

Explain Avogadro’s constant

Answer 20

One mole of an element will have same number of particles as RAM

Question 21

Explain molar mass

Answer 21

The mass of a substance with 6.02 x 10^23 particles containing same fundamental units as 12.00g of carbon-12

Question 22

Explain molar gas volume

Answer 22

Volume occupied by one mole of any gas at room temperature and pressure

Question 23

During water of crystallization practical why were multiple readings for the mass of the residue taken ?

Answer 23

To make sure all the water has been removed

Question 24

Give 2 modifications to crystallisation practical to reduce percentage uncertainty in the mass of the residue

Answer 24

• Use a balance that weighs to 3 decimal places
• Use a larger mass of residue (named)

Question 25

Give equation for oxidation of Mg

Answer 25

Mg → Mg2+ + 2e−

2 electrons lost (or more if a number is before the Mg)

Question 26

How do you obtain a solid sample from an aqueas solution ?

Answer 26

• Filter to obtain solid
• Evaporate to remove water

Question 27

How do you work out molar mass and what are the units ?

Answer 27

mass/moles
g/mol-1

Question 28

Compare electrical conductivities of solid and aqueas barium chloride in terms of particles involved

Answer 28

Barium chloride does not conduct electricity
when solid
AND
because it has ions which are fixed a lattice

Barium chloride conducts when in aqueous
solution
AND
because it has mobile ions

Question 29

How do you obtain a solid from a reaction ?

Answer 29

-Filter to obtain solid
- Dry by evaporation of water