Amount of Substance

Question 1

Define Relative Atomic Mass

Answer 1

The mean mass of an atom of an element,divided by 1/12 of the mean mass of an atom of the carbon-12 isotope

Question 2

Define Relative Molecular Mass

Answer 2

The mean mass of a molecule of a compound,divided by 1/12 of the mean mass of an atom of the carbon-12 isotope

Question 3

What is Avogadro’s constant?

Answer 3

6.022 x 10^23

Question 4

What does Avogadro’s constant allow you to find?

Answer 4

The number of particles present in a sample of a substance with known mass
Number of particles=nL
n=moles L=Avogadro constant

Question 5

What does the number in Avogadro’s constant allow you to find?

Answer 5

The number of particles present in a sample of a substance with known mass
Number of particles = nL
(n=moles)(L=Avogadro’s constant)

Question 6

How do you calculate moles?

Answer 6

Mass/Mr
Concentration x volume/1000

Question 7

What trends do gases and volatile liquids follow when under standard conditions?

Answer 7

Pressure is proportional to temperature
Volume is proportional to temperature
Pressure and volume is inversely proportional

Question 8

What is the ideal gas equation?

Answer 8

pV=nRT=mRT/Mr

Question 9

What are the standard units for the ideal question?

Answer 9

p=pressure in pascals
V=volume measured in m³
T=Temperature in Kelvin
n=moles
m=mass in grams

Question 10

What is the ideal gas constant? What is it equal to?

Answer 10

R
It is equal to 8.31JK-¹mol-¹

Question 11

What is the empirical formula?

Answer 11

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

Question 12

How is empirical formula found?

Answer 12

Using molar ratios of each element

Question 13

What is molecular formula?

Answer 13

The true number of each atom in the molecule

Question 14

How can molecular formula be determined?

Answer 14

Using the Mr of the empirical formula and the true Mr of the molecule.
This gives a multiplier value which can be used to scale up the empirical formula

Question 15

What must chemical equations be before they are used in calculations?

Answer 15

Balanced

Question 16

Why must equations be balanced before being used in calculations?

Answer 16

The reacting ratios must be correct

Question 17

How do you calculate percentage yield?

Answer 17

%yield=Experimental yield/Theoretical mass x 100

Question 18

How do you calculate atom economy?

Answer 18

%atom economy=Mr or desired product/Mr of reactants x 100

Question 19

In industrial processes, why is it desirable to have a high atom economy for a reaction?

Answer 19

There is little or no waste product, only the desired product. The process is more economically viable for industrial scale manufacture

Question 20

Why is a high atom economy beneficial for the environment?

Answer 20

It uses less natural resources and therefore uses less energy

Question 21

What is Boyle’s Law?

Answer 21

At constant temperature then the product of pressure and volume is constant
P x V = constant

Question 22

What is Charle’s Law?

Answer 22

At constant pressure then volume is proportional to the temperature
VαT
V/T = Constant

Question 23

What is Gay-Lussac’s Law?

Answer 23

At constant volume, pressure is proportional to the temperature
PαT
P/T = Constant

Question 24

What is the yield of a reaction?

Answer 24

The mass of product obtained

Question 25

What is the theoretical yield?

Answer 25

The maximum theoretical mass of product in a reaction (calculated using the idea of conservation of mass)

Question 26

What is the actual yield?

Answer 26

The mass of product you get when you actually do the reaction

Question 27

What is the percentage yield?

Answer 27

The ratio of actual mass of products obtained compared with maximum theoretical mass

Question 28

What is a titration used to measure?

Answer 28

An unknown concentration of solution by reacting it to a known concentration of another solution