C3: Quantitative chemistry

Question 1

State the law of conservation of mass

Answer 1

No atoms are gained or lost in a reaction

Question 2

Mass appears to increase during a reaction if …

Answer 2

One of the products is a gas

Question 3

Mass appears to decrease during a reaction if…

Answer 3

One of the products is a gas and it has escaped

Question 4

Balanced symbol equations;

Answer 4

Represent chemical reactions and have the same number of atoms of each element on both sides of the equation

Question 5

Chemical amounts are measured in …(4)

Answer 5

Moles.

• mass of one mole of a substance in grams = relative formula mass(Mr)
• one mole of a substance will contain the same number of particles, atoms, molecules or ions
• number of moles= mass(g)/ Mr

Question 6

Define relative formula mass.

Answer 6

The sum of of the relative atomic masses of the atoms in the number shown in the formula

Question 7

Concentration of solutions(4):

Answer 7

Measured in mass per given volume of solution (g/dm cubed)

• the greater the mass the higher the concentration
• the greater the volume the lower the concentration
• concentration= mass(g)/ volume (dm cubed)

Question 8

Dm cubed :

Answer 8

1 dm cubed = 1000 cm cubed

Question 9

Chemical measurements(2):

Answer 9

Whenever a measurement is taken there is always a degree of uncertainty.
Degree of uncertainty= mean ± range /2

Question 10

Limiting reactants(3):

Answer 10

The reactant that is completely used up, limits the amount of product that is made, less moles are made

Question 11

Atom economy(3):

Answer 11

A measure of the amount of starting materials that end up as useful product
- high atom economy is important for sustainable development and economic reasons

Atom economy=
Mr of desired product/sum of Mr of all reactants
x100

Question 12

Percentage yield(2):

Answer 12

It is comparing the amount of product as a percentage of the maximum theoretical amount

% yield= mass of product/ theoretical mass x 100

Question 13

It is not always possible to obtain the calculated amount of a product because …(3)

Answer 13

• the reaction may not be reversible
• some of the products may be lost when it is separated from the reaction mixture
• some of the reactants may react in different ways to the expected reaction

Question 14

How do you calculate the number of moles of a gas?

Answer 14

No. Of moles of a gas =

Volume of gas(dm cubed)/24dm cubed

Question 15

What is concentration measured in?

Answer 15

Mol/dm cubed

Question 16

Soluble salts(4):

Answer 16

They can be made from reacting acids with solid, insoluble substances

• add solid to acid until no more dissolves
• filter off excess solid
• crystallize to produce solid salts

Question 17

Electrolysis(5):

Answer 17

The splitting up using electricity

• when an ionic compound is molten or it is dissolved in water ions are free to move
• these are then able to conduct electricity and are called electrolytes
• passing an electric current through electrolytes causes current through electrolyte which causes the ions to move through the electrodes

Question 18

Anode(3):

Answer 18

• The positive electrode
• negative ions are attracted to it
• oxygen is formed at the anode

Question 19

Cathode(4):

Answer 19

• the negative electrode
• positive ions are attracted to it
• metals will be produced at the cathode if it is less reactive then hydrogen
• hydrogen will be produced if the metal is more reactive than hydrogen

Question 20

Strong acids

Answer 20

Are completely ionized in aqueous solutions

Question 21

Weak acids

Answer 21

Only partially ionized in aqueous solution

Question 22

Hydrogen ion concentration

Answer 22

As the pH decreases by 1 unit (becoming a stronger acid) the hydrogen ion concentration increases by 10

Question 23

Cations

Answer 23

Cations are POSITIVE they move towards the negative cathode

Question 24

Anions

Answer 24

Anions are NEGATIVE they move towards the positive anode

Question 25

Acids in aqueous

Answer 25

They produce hydrogen ions

Question 26

Alkalis in aqueous

Answer 26

Contain hydroxide ions

Question 27

Extracting metals using electrolysis

Answer 27

The process is expensive due to the large amounts of energy required to produce the electrical current

Question 28

dm3 to cm3 =

cm3 to dm3 =

Answer 28

dm3 to cm3 = x 1000

cm3 to dm3 = ÷ 1000