Gases and Stoichiometry

Question 1

Describe the general strategy for solving stoichiometric problems

Answer 1

1. Write the balanced equation (if needed).
2. Find the moles of ‘known’.
3. Use the molar ratio to find the moles of ‘unknown’.
4. Answer the question

Question 2

Equation to find moles given mass and molar mass

Answer 2

n = m/Mr

Question 3

Equation to find moles given concentration and volume of a solution

Answer 3

n = CV

Question 4

Equation to find moles given volume of gas (molar volume = 24.8L/mol)

Answer 4

n = V/24.8

Question 5

Equation to find mass given moles and molar mass

Answer 5

m = n x Mr

Question 6

Equation to find concentration given moles and volume of solution

Answer 6

C = n/V

Question 7

Equation to find volume of a gas given moles (molar volume = 24.8 L/mol)

Answer 7

V = n x Vm

Question 8

Equation to find volume of solution given moles and concentration

Answer 8

V = n/C

Question 9

Equation to find molar mass given moles and mass

Answer 9

Mr = m/n

Question 10

How to find moles of unknown given moles of known

Answer 10

n(known) x (coefficient unknown)/(coefficient known)

Question 11

Ideal gas equation, rearranged to find P

Answer 11

P = nRT/V

Question 12

Ideal gas equation, rearranged to find V

Answer 12

V = nRT/P

Question 13

Ideal gas equation, rearranged to find n

Answer 13

n = PV/RT

Question 14

Ideal gas equation, rearranged to find T

Answer 14

T = PV/nR

Question 15

Mathematical formula to describe Boyle’s Law

Answer 15

P1V1 = P2V2 (or PV = k)

Question 16

Mathematical formula to describe Charles’ Law

Answer 16

V = kT (or V1/T1 = V2/T2) where T is in Kelvin

Question 17

What are the standard laboratory conditions?

Answer 17

25 degrees Celsius (298K) and 100 kPa pressure.

Question 18

Definition of ‘fuel’

Answer 18

A substance that releases a usable amount of energy when combusted

Question 19

Definition of ‘greenhouse gas’

Answer 19

A gaseous molecule which contains polar bonds which absorb and then re-emit infra-red radiation, therefore contributing to the greenhouse effect

Question 20

General word equation when completely combusting a hydrocarbon, alcohol or ester fuel

Answer 20

Fuel + Oxygen –> Carbon dioxide + Water

Question 21

Definition of ‘acid’ (according to Bronsted-Lowry theory)

Answer 21

A proton (H+) donor

Question 22

Definition of ‘base’ (according to Bronsted-Lowry theory)

Answer 22

A proton (H+) acceptor

Question 23

Definition of alkali

Answer 23

A soluble base, that dissolves or reacts with water to produce hydroxide ions (OH-)

Question 24

Name given to a substance that can react as either an acid or a base

Answer 24

Amphoteric (or amphiprotic)

Question 25

When is an acid-base reaction also a neutralisation reaction?

Answer 25

When it produces water as a product

Question 26

Definition of acid-base reaction (Bronsted-Lowry theory)

Answer 26

Transfer of a proton (H+) from an acid to a base

Question 27

General word equation for the reaction between an acid and a metal oxide or hydroxide base

Answer 27

Base + Acid --> Water + Salt

Question 28

General word equation for the reaction between an acid and a carbonate base

Answer 28

Carbonate + Acid --> Water + Carbon dioxide + Salt

Question 29

General word equation for the reaction between water and an acid

Answer 29

Water + Acid --> Hydronium + Anion

Question 30

General word equation for the reaction between water and a molecular alkali

Answer 30

Water + Alkali --> Hydroxide + Cation

Question 31

General word equation for the reaction between a metal and oxygen

Answer 31

Metal + Oxygen --> Metal Oxide

Question 32

General word equation for the reaction between a metal and an acid

Answer 32

Metal + Acid --> Salt + Hydrogen

Question 33

General word equation for the reaction between a metal and liquid water

Answer 33

Metal + Water --> Metal hydroxide + Hydrogen

Question 34

General word equation for the reaction between a metal and steam

Answer 34

Metal + Steam --> Metal oxide + Hydrogen

Question 35

Word equation for the reaction between Iron (III) oxide and Aluminium powder, and the reaction type

Answer 35

Iron (III) oxide + Aluminium --> Iron + Aluminium Oxide This is a displacement reaction.

Question 36

In gravimetric analysis, what is meant by 'dry to constant mass'?

Answer 36

Repeated cycles of drying and weighing until at least two identical mass measurements are achieved. This ensures that no water remains in the precipitate

Question 37

In gravimetric analysis, would slight solubility of the precipitate cause an overestimation or underestimation of the analyte concentration?

Answer 37

Underestimation, because the measured precipitate mass would be lower than the true value.

Question 38

In gravimetric analysis, would loss of material (eg spashing, inefficient rinsing etc) cause an overestimation or underestimation of the analyte concentration?

Answer 38

Underestimation, because the measured precipitate mass would be lower than the true value.

Question 39

In gravimetric analysis, would impurities in the precipitate (eg soluble ions or water) cause an overestimation or underestimation of the analyte concentration?

Answer 39

Overestimation, because the measured precipitate mass would be higher than the true value.

Question 40

What is meant by 'precise' measurements?

Answer 40

When repeated measurements of the same quantity give values that are in close agreement with each other.

Question 41

What is meant by 'accurate' measurements?

Answer 41

Measurements that are close to the true value of that quantity

Question 42

What is meant if an experiment is described as 'valid'?

Answer 42

The experiment correctly investigates what it aims or claims to investigate; there is a logical connection between the results and the research question

Question 43

If experimental results are consistently lower than the true value, is this likely to be a result of systematic error or random error?

Answer 43

Systematic error

Question 44

How can systematic errors be managed?

Answer 44

Calibrating equipment (eg balances, pH meters, primary standard substances) so that all measurements reflect the true value being measured.

Question 45

How can random errors be managed?

Answer 45

Increasing the resolution of measuring apparatus, reducing the impact of subjective judgements, and controlling variables effectively.

Question 46

For the purposes of significant figures, are leading zeroes (eg in 0.0025) considered significant?

Answer 46

No - 0.0025 has two significant figures.

Question 47

For the purposes of significant figures, are trailing zeroes (eg in 6.2500) considered significant?

Answer 47

Yes - 6.2500 has five significant figures.

Question 48

How many significant figures are there in a whole number (in chemistry)?

Answer 48

The same number of significant figures as there are digits in the number.