Quantitative Chemistry

Question 1

State the law of conservation of mass

Answer 1

No atoms are lost or made during a chemical reaction so total mass of products = total mass of reactants

Question 2

In experiment, how can you easily compare mass of products with reactants?

Answer 2

Add up the mass of all the containers and the reactants and do the same with the products and their containers

Question 3

When might the total mass of products appear to be more than the reactants?

Answer 3

If a gas reacts and its particles enter the container

Question 4

When might the total mass of products appear to be less than the reactants?

Answer 4

If a gas is formed and the particles leave the container

Question 5

What is the symbol for relative formula mass?

Answer 5

Mr

Question 6

How is relative formula mass calculated?

Answer 6

It is the sum of the relative atomic masses of all atoms in the formula

Question 7

How does relative formula mass relate to conservation of mass in a balanced symbol equation?

Answer 7

Sum of relative formula masses of reactants = sum of the relative formula masses of the products

Question 8

In experiments, how can you calculate uncertainty?

Answer 8

Uncertainty = Range/2

Question 9

To how many decimal places should uncertainty be quoted?

Answer 9

The same number as the data used to calculate it

Question 10

What is the unit for mole?

Answer 10

mol

Question 11

Define a mole

Answer 11

The mass of one mole of a substance in grams is numerically equal to its relative formula mass

Question 12

The mole is a constant numerical value called the Avogrado constant, what is this number?

Answer 12

6.02 x 10(23)

Question 13

What is the equation that links moles to amount of substance and Avogrado’s constant?

Answer 13

Moles = amount of substance / 6.02x 10(23)

Question 14

What is the equation that links moles to mass and relative formula mass?

Answer 14

Moles = mass / Mr

Question 15

What are the three steps involved in calculating an unknown mass in a balanced symbol equation?

Answer 15

1. Use n = M x Mr to calculate moles
2. Use the molar ratio to find moles of unknown
3. Use M = n / Mr to calculate unknown mass

Question 16

What is the common error made when completing a reacting mass calculation?

Answer 16

Balancing numbers are used when calculating Mr

Question 17

How are kg’s converted into grams?

Answer 17

Divide by 1,000

Question 18

How are tons converted into grams?

Answer 18

Divide by 1,000,000

Question 19

How do balancing numbers relate to moles?

Answer 19

They give us the molar ratio of all substances in the reaction

Question 20

If given masses, how can you calculate molar ratios?

Answer 20

1. Use moles = M/Mr
2. Use the molar ratio to find moles of unknown
3. Convert to whole numbers by multiplying through

Question 21

What does excess reactant mean?

Answer 21

More of the reactant is used than is required

Question 22

Why add a reactant to excess?

Answer 22

To ensure all the limiting reactant is used up

Question 23

What does limiting reactant mean?

Answer 23

A reactant that is completely used up limiting the amount of product

Question 24

When performing chemical calculations, should limiting or excess reactant be used?

Answer 24

Limiting reactant

Question 25

How can you determine which reactant is in excess?

Answer 25

Calculate the moles of both reactants then compare to the molar ratio

Question 26

At room temperature, what is the value of the molar gas volume?

Answer 26

24 dm(3)

Question 27

What is the equation linking volume of gas and moles?

Answer 27

moles = volume / 24

Question 28

What unit should volue have in the molar gas equation?

Answer 28

dm(3)

Question 29

What is the most common unit of volume?

Answer 29

cm(3)

Question 30

How can you convert cm(3) into dm(3)?

Answer 30

/ 1000

Question 31

Describe the strategy for finding an unknown volume of gas in a reaction

Answer 31

1. calculate moles using n = v/24 2. use molar ratio to find moles of unknown 3. calculate volume of unknown using v = n x 24

Question 32

What are the units of concentration?

Answer 32

mol/dm(3) or g/dm(3)

Question 33

What is the equation for calculating concentration from moles?

Answer 33

concentration = moles / volume

Question 34

What is the most common unit for volume?

Answer 34

cm(3)

Question 35

What unit of volume is required for calculating concentration?

Answer 35

dm(3)

Question 36

How can you convert cm(3) into dm(3)?

Answer 36

/ 1000

Question 37

What is the equation for calculating concentration from mass?

Answer 37

concentration = mass/ volume

Question 38

How can you convert mol/dm(3) into g/dm(3)?

Answer 38

x Mr

Question 39

How can you calculate the mass of solute when given concentration and volume?

Answer 39

mass= concentration x volume x Mr

Question 40

How is the mean titration volume calculated?

Answer 40

By adding up the concordant results and dividing by the number of concordant results

Question 41

Describe the strategy for finding an unknown concentration in titration

Answer 41

1. calculate moles using n = C x v 2. use molar ratio to find moles of unknown 3. calculate concentration of unknown using C= n/V

Question 42

Why is it not possible to obtain 100% yield?

Answer 42

Reaction might be reversible. Products are lost during separation. Reactants react in unexpected ways

Question 43

What is yield?

Answer 43

The amount of product obtained

Question 44

How can you calculate % yield?

Answer 44

% yield = (actual mass/ theoretical mass) x 100

Question 45

What is atom economy?

Answer 45

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

Question 46

Why is high atom economy important?

Answer 46

Sustainable development and for economic reasons

Question 47

How can you calculate atom economy?

Answer 47

Atom economy = (Mr desired product / Mr of all reactants) x 100

Question 48

What is unusual about calculating atom economy?

Answer 48

The balancing numbers are used when calculating all the Mr's

Question 49

How can atom economy be improved?

Answer 49

By finding a use for the waste products

Question 50

What is the atom economy for a reaction where only one product is made?

Answer 50

100%