C3: Quantitative Chemistry

Question 1

what is the law of conservation of mass?

Answer 1

• states that no atoms are lost or made during a chemical reaction
• the mass of the products equals the mass of the reactants

Question 2

define relative atomic mass and relative formula mass.

Answer 2

RAM: average mass of atoms in an element taking into account masses and abundance of its isotopes Ar
RFM: sum of relative atomic mass of all atoms in the formula Mr

Question 3

what is Avogadro’s constant?

Answer 3

• the number of atoms, molecules or ions in a mole of a given substance
• the value of the constant is 6.02 x 10^23

Question 4

give the formula that links mass, molecular mass and moles together

Answer 4

mass = Mr x Moles

Question 5

state what we mean by a limiting reactant in a chemical reaction

Answer 5

• in a chemical reaction involving two reactants
• it is a common to use an excess of one of the reactants to ensure that all of the other reactant is used
• the reactant that is completely used up is called the limiting reactant because it limits the amount of products

Question 6

write down the formulae that link concentration, mole/mass and volume together
include units

Answer 6

concentration (g per dm3) = mass (g) / volume (dm3)
concentration ( mol per dm3) = nr of moles/ volume (dm3)

Question 7

what is the molar volume of a gas at room temperature and pressure?

Answer 7

1 mole of a gas at room temperature and pressure occupies 24dm 3

Question 8

what is titration?

Answer 8

• a technique for finding the concentration of a solution
• by reacting a known volume of this solution with a solution of known concentration

Question 9

delete

Answer 9

card

Question 10

why is it not always possible to obtain the theoretical amount of product in a chemical reaction

Answer 10

• the reaction may not go to completion as it is reversible
• some of the product may be lost when it is separated from the reaction mixture
• some side reactions may occur

Question 11

How is the percentage yield of a product calculated in a chemical reaction?

Answer 11

percentage yield = actual mass of a product / maximum theoretical mass of product x 100

Question 12

what is atom economy?

Answer 12

• a measure of the amount of starting materials that end up as useful products

Question 13

Give 2 reasons why it is important to have a high atom economy

Answer 13

• Less waste is produced
• More sustainable as less raw materials are used up

Question 14

. In a titration, what is
the function of a
pipette?

Answer 14

Measures one fixed volume accurately

Question 15

In a titration, what is the function of a
burette?

Answer 15

measures variable volumes accurately