Amount of a substance

Question 1

ideal gas equation

Answer 1

pV = nRT

Question 2

assumptions made about ideal gases (5 main)

Answer 2

• gases made up of molecules which are in constant random motion in straight lines
• molecules behave as rigid spheres
• pressure is due to collisions between molecules and container walls
• all collisions are perfectly elastic (no energy lost)
• temperature of the gas is directly proportional to the kinetic energy of the particles

Question 3

2 absolute key assumptions made about ideal gases

Answer 3

• there are no (entirely negligible) forces between molecules
• the volume occupied by the molecules is negligible compared to the volume of the container

Question 4

atom economy

Answer 4

the proportion of the total mass of the products that is in the desired product

Question 5

percentage yield

Answer 5

compares the amount produced to the amount that should have been produced

Question 6

amount of a substance

Answer 6

quantity with units mol, used as a means of comparing any species such as atoms, ion, molecules

Question 7

Avogadro constant

Answer 7

6.03 x 10^23

Question 8

water of crystallisation

Answer 8

water molecules bonded into the crystalline structure of a compound

Question 9

standard solution

Answer 9

solution of known conc

Question 10

moles of a gas

Answer 10

vol (dm3) / 24dm3

Question 11

method for finding relative molecular mass of a gas

Answer 11

• using ideal gas
• add small sample of the volatile liquid to a syringe through a needle
• weigh syringe
• inject into gas syringe through self-sealing rubber cap
• reweigh small syringe to find mass of liquid
• place gas syringe in boiling water bath at 100 degrees
• liquid vaporises and pressure recorded
• use ideal gas to calc unknowns

Question 12

atom economy =

Answer 12

sum of molar mass of desired products / sum of all molar mass of products

Question 13

relative isotopic mass

Answer 13

mass of an isotope relative to the mass of a 1/12 of carbon12

Question 14

method for finding water of crystallisation of a hydrated salt

Answer 14

• weigh crucible
• add sample of salt
• reweigh
• use pipe-clay triangle to support crucible on tripod
• heat gently with Bunsen for 1 min
• heat strongly for 3 more mins
• remove and let cool
• reweigh
• find moles of anhydrous salt formed
• find moles water lost
• find ratio of moles

Question 15

assumptions about method of finding water of crystallisation of a hydrated salt (2)

Answer 15

1) all water is lost
- solution: heat until constant mass
2) no further decomposition has occurred - hard to tell as no colour change