Topic 3 - Quantitive Chemistry

Question 1

What’s the formula for percentage mass of an element in a compound

Answer 1

((Ar x number of atoms in that element) ÷ Mr of the compound ) × 100

Question 2

What is one mole of any substance

Answer 2

An amount of that substance that contains an avogadro’s number of particles

Question 3

What’s the value of avogadro’s constant

Answer 3

6.02 × 10^23

Question 4

What is the mass of one mole of atoms in any substance equal to

Answer 4

The relative formula mass

Question 5

What’s the equation linking mass, moles, and Mr

Answer 5

Moles = mass÷ Mr

Question 6

What is the law of conservation of mass

Answer 6

During a chemical reaction no atoms are destroyed and no atoms are created - due to this no mass is lost or gained

Question 7

Why might the mass seem to change in a reaction

Answer 7

• if there is a gas involved and the reaction happens in an unsealed reaction vessel

Question 8

In a symbol equation, what tells us how many moles of each substance there are

Answer 8

The big numbers in front of the chemical formulas

Question 9

When is a reactant limiting

Answer 9

When it is used up before the others - any other reactant is it excess

Question 10

What is the amount of product formed dependent on

Answer 10

The amount of the limiting reactant

Question 11

At room temperature and pressure how much does one mole of gas occupy

Answer 11

24 dm^3

Question 12

What’s the formula for the volume of a known mass at r.t.p

Answer 12

Volume = (mass of gas ÷ Mr of gas) × 24

Question 13

What’s the equation for concentration of a solution

Answer 13

Mass of solute or number of moles of solute ÷ volume of solvent

Question 14

How do you calculate the mass of a solute in a solution

Answer 14

Concentration x volume

Question 15

How do you convert cm^3 to dm^3

Answer 15

Divide by 1000

Question 16

How to convert mol/dm^3 to g/dm^3

Answer 16

Use the equation mass = moles x Mr

Question 17

What’s the equation for atom economy

Answer 17

Atom economy =( relative formula mass of desired product ÷ relative formula mass of all reactants) × 100

Question 18

Why are reactions with a higher atom economy better

Answer 18

• reactions with a low atom economy use up resources quickly making them unsustainable and unprofitable
• they don’t produce as much waste products

Question 19

What reactions typically have the highest atom economy

Answer 19

The ones that only have one product

Question 20

What’s the equation for percentage yield

Answer 20

(Mass of product actually made ÷ maximum theoretical mass of product) × 10p

Question 21

Why is a higher percentage yield better

Answer 21

Reduced waste and reduced cost

Question 22

Why are yields below 100 percent

Answer 22

1) not all reactants react to make a product
2) there may be side reactions
3) you may lose some product when you separate it from the reaction mixture