2.1.3 Amount of Substance

Question 1

What is amount of substance?

Answer 1

Number of particles in a substance

Question 2

Mass, moles and molar mass equation?

Answer 2

n = m/mr

mr no mr

Question 3

Avogadro’s constant equation?

Answer 3

n = no. of particles/ avo.

Question 4

What is molar mass? Unit?

Answer 4

Mass (g) per mole of a substance

gmol-1

Question 5

What is molecular formula?

Answer 5

No. and type of atoms of each element in a molecule

Question 6

What is empirical formula?

Answer 6

Simplest whole number ratio of atoms of each element in a compound

Question 7

Why is empirical formula useful?

Answer 7

Giant crystalline structure- molecular would be in millions, e.g NaCl

Question 8

What is relative molecular mass?

Answer 8

Mass of a simple molecule relative to the mass of an atom of C-12

Question 9

How do you calculate relative molecular mass?

Answer 9

Add up relative atomic masses of each element in periodic table

Question 10

What is relative formula mass?

Answer 10

Mass of giant structures relative to the mass of an atom of C-12

Question 11

How do you calculate empirical formula from data?

Answer 11

1. Convert into moles

2. Divide by smallest whole number

Question 12

How do you calculate molecular formula from data?

Answer 12

1. Convert into moles (% treated like mass)
2. Find empirical
3. Find relative mass (add up all atomic masses from PT)
4. Mass of compound/ relative mass of empirical to find scale factor
5. Empirical x Scale factor

Question 13

What is a hydrated salt/ water of crystallisation?

Answer 13

A crystalline structure that contains water

Question 14

What is an anhydrous salt?

Answer 14

A crystalline structure that does not contain water

Question 15

Method to determine the water of crystallisation in hydrated salts?

Answer 15

1. Weigh crucible
2. Add salt- weigh
3. Heat for 5 mins
4. Cool- weight
   5 Calc. moles of anhydrous salt
5. Calc. moles of water
6. Find empirical formula of salt:water

Question 16

Flaws in the method of determining the water of crystallisation in hydrated salts?

Answer 16

1. Not all water has been lost- heat to constant mass

2. Salts can decompose to diff. salts

Question 17

How do you convert from dm3 to cm3?

Answer 17

Dm3 x 1000 = cm3

Cm3 / 1000 = dm3

Question 18

What is concentration? Units?

Answer 18

Amount of solute, in moles or grams, dissolved in each 1dm3 of solution
moldm-3 or gdm-3

Question 19

What is a standard solution?

Answer 19

Solution of known concentration and volume

Question 20

Moles, concentration, volume equation?

Answer 20

n = c x v

no more caravans

Question 21

What is molar gas volume? Units?

Answer 21

Volume per mole of gas molecules at a known temp and pressure
dm3mol-1

Question 22

What is room temperature and pressure that most experiments are set in?

Answer 22

T: 20C
P: 101kPa

Question 23

Vol of gas, moles and molar gas vol equation?

Answer 23

Vol of gas = moles x 24 (if RTP)

Vol of gas = moles x molar volume

Question 24

What is the ideal gas equation?

Answer 24

pV = nRT

Question 25

Units of ideal gas equation?

Answer 25

Pressure = Pa
Volume = m3
Moles = mol
Temp = K

Question 26

What is stoichiometry?

Answer 26

Balanced ratio of moles in an equation

Question 27

What is theoretical yield?

Answer 27

Max. possible amount of product produced from a reaction

Question 28

What is actual yield?

Answer 28

The actual amount of product produced from a reaction (actual

Question 29

What is percentage yield?

Answer 29

How much of the theortical yield you made (%)

Question 30

What is the percentage yield calculation?

Answer 30

(Actual/theoretical)x100

Question 31

What is a limiting reagent?

Answer 31

Reactant not in excess and will be used up first and stop the reaction

Question 32

What is atom economy?

Answer 32

How well atoms have been utilised in a chemical equation

Question 33

What is the atom economy calculation?

Answer 33

Atom ec. = total molar masses of desired products/ total molar masses of all products