1 Principles of Chemistry

Question 1

What are the three states of matter?

Answer 1

Solids, liquids and gases

Question 2

What are the four state changes

Answer 2

Melting (solid → liquid) when heating up
Freezing (liquid → solid) when cooling down
Boiling (liquid → gas) when heating up
Condensing (gas → liquid) when cooling down

Question 3

What is the arrangement of particles, the movement of particles, and the closeness of particles for solids?

Answer 3

Regular arrangement, vibrate about a fixed position, very close.

Question 4

What is the arrangement of particles, the movement of particles, and the closeness of particles for liquids?

Answer 4

Randomly arranged, move around each other, close.

Question 5

What is the arrangement of particles, the movement of particles, and the closeness of particles for gases?

Answer 5

Randomly arranged, move quickly in all directions, far apart.

Question 6

Interconversion:
Melting = ?
Boiling = ?
Freezing =?
Evaporation = ?
Condensation = ?
Sublimation = ?

Answer 6

Solid to a liquid
Liquid to a gas
Liquid to a solid
Liquid to a gas
Gas to a liquid
Solid to a gas

Question 7

Solutions table:
1. Solvent meaning and example?
2. Solute meaning and example?
3. Solution meaning and example?
4. Saturated solution meaning and example?
5. Soluble meaning and example?
6. Insoluble meaning and example?

Answer 7

1. The liquid in which a solute dissolves - the water in sea water.
2. The substance which dissolves in a liquid to form a solution - the salt in seawater.
3. The mixture formed when a solute is dissolved in a solvent - seawater.
4. A solution with the maximum concentration of solute dissolved in the solvent - seawater in the dead sea.
5. Describes a substance that will dissolve - salt is soluble in water.
6. Describes a substance that won’t dissolve - sand is insoluble in water

Question 8

Element definition and examples?

Answer 8

Substances that cannot be broken down into anything simpler because they are made of only one type of atom. Hydrogen, oxygen, carbon

Question 9

Compound definition and examples?

Answer 9

A pure substance made up of two or more elements chemically combined together. They cannot be separated by physical means. Calcium carbonate, carbon dioxide.

Question 10

Mixture definition and examples?

Answer 10

A combination of two or more substances that are not chemically joined together. Can be separated by physical means. Salt and water (seawater), air.

Question 11

How do you determine whether a substance is pure?

Answer 11

Pure substances melt and boil at specific and sharp temperatures e.g. pure water has a boiling point of 100 degrees celcius and a melting point of 0 degrees celcius.

Question 12

How do you determine whether a substance is a mixture?

Answer 12

Mixtures have a range of melting and boiling points as they consist of different substances that tend to lower the melting point and broaden the melting point range.

Question 13

What is simple distillation?

Answer 13

It is used to separate a liquid and soluble solid from a solution (e.g. water from a solution of salt water) or a pure liquid from a mixture of liquids.

Question 14

What is fractional distillation?

Answer 14

This is used to separate two or more liquids that are miscible with one another (e.g. ethanol and water from a mixture of the two)

Question 15

How do you carry out a fractional distillation experiment?

Answer 15

The solution is heated to the temperature of the substance with the lowest boiling point
This substance will rise and evaporate first, and vapours will pass through a condenser, where they cool and condense, turning into a liquid that will be collected in a beaker
All of the substance is evaporated and collected, leaving behind the other components(s) of the mixture
For water and ethanol
Ethanol has a boiling point of 78 ºC and water of 100 ºC
The mixture is heated until it reaches 78 ºC, at which point the ethanol boils and distills out of the mixture and condenses into the beaker
When the temperature starts to increase to 100 ºC heating should be stopped. Water and ethanol are now separated.

Question 16

What is filtration?

Answer 16

It is used to separate an undissolved solid from a mixture of the solid and a liquid/solution (e.g. sand from a mixture of sand and water)

Question 17

How to carry out a filtration experiment?

Answer 17

A piece of filter paper is placed in a filter funnel above a beaker
A mixture of insoluble solid and liquid is poured into the filter funnel
The filter paper will only allow small liquid particles to pass through as filtrate
Solid particles are too large to pass through the filter paper so will stay behind as a residue.

Question 18

What is crystallisation?

Answer 18

It is used to separate a dissolved solid from a solution, when the solid is much more soluble in hot solvent than in cold (e.g., copper sulphate from a solution of copper (II) sulphate in water)

Question 19

How to carry out a crystallisation experiment?

Answer 19

The solution is heated, allowing the solvent to evaporate, leaving a saturated solution behind. Test if the solution is saturated by dipping a clean, dry, cold glass rod into the solution. If the solution is saturated, crystals will form on the glass rod. The saturated solution is allowed to cool slowly. Crystals begin to grow as solids will come out of solution due to decreasing solubility
The crystals are collected by filtering the solution, they are washed with cold distilled water to remove impurities and are then allowed to dry.

Question 20

What is paper chromatography?

Answer 20

This technique is used to separate substances that have different solubilities in a given solvent (e.g. different coloured inks that have been mixed to make black ink)

Question 21

How to carry out a paper chromatography experiment?

Answer 21

A pencil line is drawn on chromatography paper and spots of the sample are placed on it. Pencil is used for this as ink would run into the chromatogram along with the samples
The paper is then lowered into the solvent container, making sure that the pencil line sits above the level of the solvent, so the samples don’t wash into the solvent container
The paper is called the stationary phase
The solvent travels up the paper by capillary action, taking some of the coloured substances with it; it is called the mobile phase
Different substances have different solubilities so will travel at different rates, causing the substances to spread apart
Those substances with higher solubility will travel further than the others
This will show the different components of the ink / dye
If two or more substances are the same, they will produce identical chromatograms
If the substance is a mixture, it will separate on the paper to show all the different components as separate spots
An impure substance will show up with more than one spot, a pure substance should only show up with one spot

Question 22

Rf Values

Answer 22

These values are used to identify the components of mixtures The Rf value of a particular compound is always the same but it is dependent, however, on the solvent used. If the solvent is changed then the value changes. Calculating the Rf value allows chemists to identify unknown substances because it can be compared with Rf values of known substances under the same conditions. These values are known as reference values

Question 23

How to calculate the Rf value?

Answer 23

Rf = distance travelled by substance ÷ distance travelled by solvent.
The Rf value will always lie between 0 and 1; the closer it is to 1, the more soluble is that component in the solvent
The Rf value is a ratio and therefore has no units

Question 24

What is the definition of an atom?

Answer 24

The smallest particles of an element that consists of electrons surrounding a nucleus that contains protons and neutrons.

Question 25

What is the definition of a molecule?

Answer 25

A group of two or more atoms chemically joined together forming an identifiable unit which retains the properties and composition of the substance.

Question 26

Relative atomic mass

Answer 26

One relative atomic mass unit is equal to one twelfth the mass of a carbon-12 atom.
All other elements are measured relative to the mass of a carbon-12 atom and since these are ratios, the relative atomic mass has no units
Hydrogen for example has a relative atomic mass of 1, meaning that 12 atoms of hydrogen would have exactly the same mass as 1 atom of carbon.

Question 27

What is the relative mass and charge of:
a proton
a neutron
an electron

Answer 27

proton has RM 1, charge +1
neutron has RM 1, Charge 0
electron RM 1/1840, charge -1

Question 28

Atomic number definition

Answer 28

The number of protons in the nucleus of an atom

Question 29

Mass number definition

Answer 29

The sum of the number of protons and neutrons in the nucleus of an atom.

Question 30

Isotopes definition

Answer 30

Atoms of the same element which contain the same number of protons and electrons but a different number of neutrons. Therefore, they have the same atomic number but a different mass number.

Question 31

Relative atomic mass definition

Answer 31

The weighted average mass of one atom of an element, taking into account the abundance of all the isotopes of that element. It is measured as a ratio 1/12 of the mass of an atom of carbon-12.

Question 32

How to calculate relative atomic mass

Answer 32

The relative atomic mass of each element is calculated using the mass number and the relative abundances of all the isotopes of a particular element. To calculate the relative atomic mass:
Multiply the % abundance of each isotope by its mass
Add these numbers together
Divide by the total abundance (which when using % abundance, will be 100%)

Question 33

Relative Atomic Mass (Ar) equation

Answer 33

Ar = (% of isotope A x mass of isotope A) + (% of isotope B x mass of isotope B) divided by 100

Question 34

What does the period show? (In the periodic table)

Answer 34

These are the horizontal rows that show the number of shells of electrons an atom has and are numbered from 1 - 7

Question 35

What does the group show?

Answer 35

These are the vertical columns that show how many outer electrons each atom has and are numbered from 1 – 7, with a final group called group 0 (instead of group 8)

Question 36

Characteristic properties of metals (Electron arrangement, Bonding, Electrical conductivity, Type of oxide, Reaction with acids, Physical characteristics)

Answer 36

Electron arrangement = 1-3 outer shell electrons (More in periods 5 + 6)
Bonding = metallic due to the loss of outer shell electrons
Electrical conductivity = Good conductors of electricity
Type of oxide = Basic oxides (a few are amphoteric)
Reaction with acids = Many react with acids
Physical characteristics = Malleable, can be bent and shaped. High melting and boiling point.

Question 37

Characteristic properties of non-metals (Electron arrangement, Bonding, Electrical conductivity, Type of oxide, Reaction with acids, Physical characteristics)

Answer 37

Electron arrangement=4-7 electrons in the outer shell
Bonding=Covalent by sharing of outer shell electrons
Electrical conductivity=Poor conductors of electricity
Type of oxide=Acidic oxides (some are neutral)
Reaction with acids=Do not react with acids
Physical characteristics=Flaky, brittle. Low melting and boiling point.

Question 38

What is the Law of Conservation of Mass?

Answer 38

The total mass of reactants is always equal to the total mass of products.

Question 39

How to calculate the % mass of an element?

Answer 39

(Ar x number of atoms in the element / Mr of the compound) x 100

Question 40

Write down the equation that links moles, mass in grams and the molar mass.

Answer 40

Moles = mass / molar mass

Question 41

What is the equation to calculate the percentage yield?

Answer 41

(actual yield/theoretical yield) x 100

Question 42

What is empirical formula?

Answer 42

It gives the simplest whole number ratio of atoms of each element in the compound.

Question 43

What is molecular formula?

Answer 43

It gives the exact numbers of atoms of each element present in the formula of the compound.