Quantitative Chemistry

Question 1

What happens to mass in chemical reaction

Answer 1

It is conserved

Question 2

Law of conservation of mass

Answer 2

No atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants

Question 3

Percentage mass of an element in a compound

Answer 3

• element’s Ar X number of atoms of that element
• ÷ Mr of compound
• X100

Question 4

Why might mass seem to change during a reaction

Answer 4

• one of the reactants is a gas, all products solid/liquid/aqueous
• one of the products is a gas, all reactants solid/liquid/aqueous

Question 5

How does a reactant being a gas cause mass to seem to change

Answer 5

• before reaction - gas floating in air, not contained in unsealed reaction vessel, its mass can’t be accounted for
• gas reacts to form products - becomes contained in reaction vessel, its mass now accounted for
• mass inside reaction vessel increases

Question 6

How does product being a gas cause mass to seem to change

Answer 6

• before reaction, all reactants contained in unsealed reaction vessel, all mass accounted for
• reactants react to form gas product - gas can escape from reaction vessel, its mass can’t be accounted for
• mass inside reaction vessel decreases

Question 7

How to get more accurate measurement on mass in a reaction

Answer 7

Have reaction take place in sealed container

Question 8

1 mole of a substance

Answer 8

Amount of that substance that contains Avogadro’s constant number of particles (atoms/molcules/ions/electrons) - 6.02x10²³

Question 9

What is the Ar or Mr of a substance equal to

Answer 9

1 mole

Question 10

Mass, Mr, moles triangle

Answer 10

• Mr
• mass
• moles

Question 11

How to know number of moles of a substance from chemical formula

Answer 11

Big number is number of moles

Question 12

How to balance equations using reacting masses

Answer 12

• find moles of each substance (mass/Mr)
• divide number of moles of substance by smallest number of moles - this gives you the big number
• put each substances big number in front of it in equation

Question 13

When do reactions stop

Answer 13

When all of 1 reactants is used up

Question 14

Excess reactant

Answer 14

The reactant that is NOT used in a reaction

Question 15

What is usually done with excess reactants

Answer 15

Added in excess to make sure other reactant used up

Question 16

Limiting reactant

Answer 16

The reactant that IS used up in a reaction

Question 17

Relationship between limiting reactant and amount of product formed

Answer 17

Directly proportional

Question 18

How to calculate mass of product formed using limiting reactant

Answer 18

• write balanced equation
• work out Mr of mass you want and mass from question, IGNORING big numbers
• find number of moles of mass you know (mass/Mr)
• use molar ratio to find number of moles in substance you want mass of
• find mass of substance (Mr X moles)

Question 19

Which substance is ignored when finding mass of product formed using limiting reactant

Answer 19

Reactant in excess

Question 20

Concentration

Answer 20

Amount of substance in a certain volume of solution

Question 21

How is concentration measured

Answer 21

Mass per given volume of solution

Question 22

What is a more concentration solution

Answer 22

Solution with more solute in a given volume

Question 23

Concentration, volume, mass triangle

Answer 23

• concentration
• mass
• volume