Chapter 1: Stoichiometry

Question 1

What are elements?

Answer 1

Made up of a single type of atom.

Question 2

What are Isotopes?

Answer 2

Atoms of an element which contain a different amount of neutrons, therefore have different physical properties.

Question 3

What are compounds?

Answer 3

Two or more elements chemically combined in fixed ratios.

Question 4

What is atom economy and its equation?

Answer 4

The atom economy of a reaction is its efficiency to produce a specific product.
(Mass of desired products/total mass of products) x 100

Question 5

What are mixtures?

Answer 5

A mixture is a composition of elements/compounds in which there is no chemical combination.

Question 6

What is the Kinetic theory of matter?

Answer 6

The average kinetic energy of particles are directly related to the temperature of a system.
KE is proportional to Temperature (Kelvin)

Question 7

Why does diffusion only occur in fluids?

Answer 7

As particles in fluids can flow over each other in random motions, therefore can disperse evenly.

Question 8

Why do substances with lower masses diffuse more quickly at the same temperature than those with a greater mass?

Answer 8

As the kinetic energy of particles is equal at the same temperature, regardless of the nature of the substance - there is an inverse relationship between mass and velocity (KE = 1/2mv^2), therefore the greater the mass - the less the speed of particles, thus a lower rate of diffusion.

Question 9

What is the change of state from solid to gas?

Answer 9

Sublimination

Question 10

What is the change of state from gas to solid?

Answer 10

Deposition

Question 11

What is the difference between evaporation and boiling of a substance?

Answer 11

Evaporation is the change of state from liquid to gas which occurs at the surface of a liquid whereas in boiling, change of state occurs throughout.

Question 12

When does boiling take place?

Answer 12

When vapour pressure reaches external pressure.

Question 13

What happens to boiling water at higher altitudes?

Answer 13

At higher altitudes, lower external pressure will lower the boiling point of water as lesser temperatures will be required to transfer adequate energy to the water in order for vapour pressure to reach external pressure.

Question 14

How do pressure cookers work?

Answer 14

A pressure cooker increases the pressure, thereby increasing the boiling point of water as greater energy must be transferred to it in order for vapour pressure to reach external pressure, allowing for food to cook faster as the water reaches higher temperatures.

Question 15

Why does the temperature stay constant at the plateaus of the change of state graph?

Answer 15

As energy being transferred is being used to break intermolecular forces between particles in order for a change of state.

Question 16

What is Avogadro’s constant?

Answer 16

6.02 x 10^23 is the number of particles, atoms, molecules in one mole of any substance.

Question 17

What is relative atomic mass?

Answer 17

The weighted mass of an atom compared to 1/12 of an atom of Carbon-12.

Question 18

What is an amu?

Answer 18

An atomic mass unit is the mass of 1/12 of a carbon atom.

Question 19

Why is Carbon-12 used as a reference point for the relative scale of masses of atoms?

Answer 19

As Carbon-12 is the most abundant isotope of Carbon and its mass can be measured accurately.

Question 20

What is the relative formula mass?

Answer 20

The sum of all relative atomic masses of atoms in a formula unit of a substance(Ionic compounds)

Question 21

What is the relative molecular mass?

Answer 21

The sum of all relative atomic masses of atoms in a formula unit of a substance(molecular covalent bonds)

Question 22

Why do mols of different substances have the same number of particles but weigh differently?

Answer 22

As atoms of different elements have different masses.

Question 23

How do you calculate the mass of one molecule?

Answer 23

Molar mass/Avogadro’s constant

Question 24

What is the empirical formula of a substance?

Answer 24

The simplest whole-number ratio of atoms in a compound whereas the molecular formula is the actual number

Question 25

How do you calculate percentage composition?

Answer 25

(Mass of an element in a compound/molar mass) x 100

Question 26

What is the Limiting reactant?

Answer 26

The reactant which limits the amount of product formed, whereas the other reactant is in excess.

Question 27

What is the equation for percentage yield?

Answer 27

(actual/experimental yield/theoretical yield) x 100

Question 28

What is the difference between homogenous and heterogenous mixtures?

Answer 28

A homogenous mixture has uniform composition & properties throughout whereas a heterogenous mixture does not.

Question 29

What is a solution?

Answer 29

A homogenous mixture of 2 or more substances, solute in a solvent.

Question 30

What units are the concentration of a solution measured in?

Answer 30

mol dm^-3 or g dm^-3

Question 31

How to calculate the parts per million of a solution of very low conc?

Answer 31

(mass of component/mass of solution) x 1,000,000 1 ppm = 1 mg of solute in 1 kg/l/dm3 of solution

Question 32

What is used to describe multiple dilutions of a solution, usually by the same factor?

Answer 32

Serial dilutions

Question 33

What comprises a standard solution?

Answer 33

Made of a primary standard with high purity (99.9%), high molar mass, low reactivity and does not change composition in contact with air.

Question 34

Why should NaOH not be used to make a primary standard solution?

Answer 34

As it is a hygroscopic substance, therefore absorbs moisture from the air.

Question 35

What is a secondary standard solution?

Answer 35

A solution that has been standardised using a primary standard solution.

Question 36

What is the Kinetic molecular theory of gases?

Answer 36

Particles in a gas follow random, straight-line motion. There are negligible forces of attraction between particles. Collisions between particles/container are perfectly elastic (no energy is lost) Distance between particles is much more greater than the size of particles (negligible volume) Kinetic energy is directly proportional to the absolute temp.

Question 37

What is Avogadro's Law?

Answer 37

Equal volumes of all gases, when measured at the same pressure and temperature contain an equal amount of particles and vice versa.

Question 38

What is the volume of one mole of gas at standard conditions?

Answer 38

22.7 dm^3 mol^1

Question 39

What is the relationshio between pressure and volume?

Answer 39

With constant temp, any increase in pressure on a fixed mass of gas results in a decrease in volume.

Question 40

What is the relationship between volume and temperature?

Answer 40

As the volume of a gas is increased as the temperature increases, at a fixed mass.

Question 41

What is the relationship between pressure and temperature?

Answer 41

At a constant volume, any increase in pressure of a gas of a fixed mass will result in a proportional increase in its temperature

Question 42

How do real gases differ from the kinetic molecular theory of gases/ideal gas laws?

Answer 42

At high pressures, intermolecular forces between particles become significant as particles are closer together. At lower temps as well. The non-zero volume of particles become significant as this volume contributes to the total volume of gas.

Question 43

What kinds of gases show the most ideal behaviour?

Answer 43

Gases with a low molar mass and weak intermolecular forces