2.1.3 Amount Of Substance

Question 1

Mole

Answer 1

Amount of substance in gramd that has the same number of particles as there are atoms in 12 grams of carbon-12

Question 2

Relative atomic mass

Answer 2

Average mass of one atom compared to 1/12th mass of one atom of carbon-12

Question 3

Molar mass

Answer 3

Mass in grams of one mole of a substance and is given in units g/mol

Question 4

Molar gas volume

Answer 4

Volume one mole of gas at given temperature and pressure, all gases have this volume

Question 5

Room temperature and pressure

Answer 5

1atm

25 degrees

Question 6

Molar gas volume at RTP

Answer 6

24 dm3

24,000 cm3

Question 7

Avogadros constant

Answer 7

6.02 x 10^23 atoms in 12 grams of carbon-12

Question 8

calculate moles

Answer 8

Mass divided by mr

Question 9

Empirical formulae

Answer 9

Simplist whole number ratio of atoms of each element in the compound

Question 10

Method to work out empirical formula

Answer 10

1. Divide each mass by atomic mass of element
2. Divide each answer from step one by lowest number in that stage
3. Multiply to adjust ratio to whole numbers

Question 11

Molecular formula

Answer 11

Actual number of atoms of each element in the compound

Question 12

Hydrated salt practical

Answer 12

Weigh empty crucible and lid
Add hydrated copper sulfate and weigh again
Heat using Bunsen burner
Allow to cool
Weigh crucible and contents again
Heat crucible again and reweigh until you reach a constant mass

Question 13

Why must crucible be dry at the start of experiment

Answer 13

As a wet crucible would give an inaccurate result

Cause mass loss to be too large as water would be lost when heating

Question 14

Two assumptions made in copper sulfate practical

Answer 14

1. All water is evaporated

2. No further decomposition occurs

Question 15

Calculating moles using conc

Answer 15

n= conc x volume x 10^-3

Unit is dm^3

Question 16

Making a standard solution

Answer 16

Weigh sample bottle with mass of solid 
Transfer to beaker and reweigh bottle
Record mass difference
Add 100 cm3 of water and use a glass rod to dissolve solid
Heat gently to help dissolve
Pour into 250cm3 flask using a funnel 
Rinse beaker and funnel and add washings into flask
Fill to mark 
Invert several times

Question 17

Diluting a solution

Answer 17

Pipette 25cm3 of original solution into 250cm3 volumetric flask
Make up to mark with distilled water using dropping pipette
Invert several times

Question 18

Calculating dilutions

Answer 18

New conc = old conc x old vol/new vol

Question 19

Safety hazards

Answer 19

Irritant- dilute acids and alkalis, wear glasses
Corrosive-stronger acid and alkalis wear goggles
Flammable-keep away from naked flames
Toxic-wear gloves, avoid skin contact, wash hands after use
Oxidising- keep away from flammable or easily oxidised materials

Question 20

ideal gas equation

Answer 20

PV=nRT

Question 21

Units for ideal gas equation

Answer 21

Pressure= pascals 
Volume= m^3
Temp= K
n=moles
R = 8.314 J/K/mol

Question 22

Potential errors using a gas syringe

Answer 22

Gas escapes before bung inserted
Syringe sticks
Some gases are soluble in water so true amount isn’t measured

Question 23

Reacting volumes of gas

Answer 23

Equal volumes of gas measured under same conditions of temperature and pressure contain equal number of moles

Question 24

Number of particles calculation

Answer 24

mol x avogadros constant

Question 25

Density calculation

Answer 25

Mass/volume

Question 26

% yield

Answer 26

Actual/theoretical x 100

Question 27

Atom economy

Answer 27

Mass useful/ mass all reactants x100

Don’t use balancing numbers