2.1.3 Amount Of Substance

Question 1

What is a mole?

Answer 1

One mole of a substance contains as many substance units are there are atoms in 12g of the carbon-12 isotope.

Question 2

What is Avogadro’s constant?

Answer 2

6.02x1023 atoms
No of particles (atoms, molecules, ions, electrons) in one mol

Question 3

What is molar mass?

Answer 3

Mr
Found by adding together all the atomic masses for each unit in a formula
gmol-1

Question 4

What is molar gas volume?

Answer 4

Gas volume per mol
dmmol-3

Question 5

What is empirical formula?

Answer 5

The simplest whole number ratio of atoms of each elements in a compound

Question 6

What is the mol equation?

Answer 6

mol = mass/Mr

Question 7

What is anhydrous?

Answer 7

A compound without water

Question 8

What does hydrated mean?

Answer 8

Compound containing water

Question 9

What is water of crystallisation?

Answer 9

The amount of water molecules which are present in one formula unit of salt

Question 10

What is the mol, conc and vol equation?

Answer 10

Conc = mol/vol

Question 11

What is the mol and vol equation?

Answer 11

Mol = vol/24
(In dm3)
Or can use 24,000 if in cm3

Question 12

How to calculate percentage composition?

Answer 12

(No of atoms) x (Mr)
/ RFM. X 100

Question 13

What are gas laws?

Answer 13

• 1 mol of gas takes up same vol as 1 mol of another gas
• equal nos of gas occupy same vol
• vol of any gas is 24cm3 at room temp and pressure

Question 14

What are the properties of ideal gases?

Answer 14

• lack of IM forces - neither attract nor repel
• elastic collisions - no energy lost
• zero particle vol - so small compared to empty space vol is negligible

Question 15

What is the ideal gas equation?

Answer 15

pV = nRT

p = pressure (Pa) - 1atm is 101,325Pa
V = vol (m3) - 1,000dm3 in m3
n = mol
R = gas constant (given)
T = temp IN KELVIN

Question 16

What is conc?

Answer 16

Amount of substance dissolve in given vol
Moldm-3 or gdm-3

Question 17

What are the conc equations?

Answer 17

Conc = mol/vol(dm3)

Conc = mass/vol

Question 18

How to make a standard solution?

Answer 18

1. Find Mr of compound. To make 1 mol, you need same mass as Mr
2. Dissolve in distilled water and make up to one litre - the conc will be 1mol/dm3 (add to volumetric flask)
3. Can divide to e.g. 200cm3

Question 19

What is percentage yield equation?

Answer 19

Percentage yield = actual / theoretical x100

Question 20

How can errors be made affecting percentage yield?

Answer 20

• reaction may be at equilibrium
• side reactions may occur
• reactants may not be pure
• some reactants or products may be left behind in apparatus
• separation and purification may result in loss of some product

Question 21

How do you calculate atom economy?

Answer 21

Atom economy = mr of desired product / mr of total product x 100

Or reactant
(Always use big number)

Question 22

How do you calculate percentage uncertainty?

Answer 22

Percentage error = error in reading / value measured x100

Question 23

Simple titration method

Answer 23

1. Measure alkali using a pipette and add to conceal flask with indicator, e.g. phenolphthalein
2. Do a rough first to see where end point. Measure acid in burette and add to alkali, swirling. Stop when a permanent colour change occurs. Record final reading on burette.
3. Do accurate titration, run to 2cm3 of end point and then add drop by drop.
4. Work out titre
5. Repeat until concordant results are achieved (within 0.1cm3)
6. Wash out flask between to remove leftover alkali or acid

Question 24

Titration indicator colours

Answer 24

Phenolphthalein
Colourless in acid
Pink in alkaline

Methyl orange
Yellow in alkaline
Red in acid

Question 25

How to convert from cm3 to dm3?

Answer 25

/ 1000

Question 26

What is the mol of gas and vol equation?

Answer 26

Mol = vol / 24(dm3) or 24000cm3