Chemistry paper 1

What is electrolysis?

the passing of an electric current throguh ionic substances that are molten or in a solution to break them down into elements, ions are discharges at electrodes to produce the elements

What is an electrolyte?

The liquid/solution which conducts electricity

What is a cathode and what is an anode?

Cathode is the negative electrode, anode is the positive electrode

What occurs at the cathode and what occurs at the anode during electrolysis?

reduction occurs at the cathode, oxidation occurs at the anode

In aqueoud electrolysis, which element is discharges at the cathode? oxygen is produced at the anode unless what?

The less reactive element discharges at the cathode. Hydrogen is produces unelss there is a less reactive metal, in which case the said metal is produces. Oxygen is produced at the anode unless the solution contains halide ions, in which case halogen moelcules are produced

How is aluminium manufactured? why is it expensive?

Aluminium is made throguh the electrolysis of aluminium and cryolite
Lots of energy is needed to produce the current in electrolysis whcih makes this process expensive

What are the half equations in the extraction of aluminium?

Al^3+ + 3e\- --\> Al (cathode)
2O^2\- --\> O2 +4e- (anode)
some oxygen reacts with carbon of the anode producing CO2

Why is cryolite used in the electrolysis of aluminium oxide?

It lowers the melting point of alumium oxide, reducing energy costs

What is oxidation/reduction?

Oxidation is loss of electrons
Reduction is gain of electrons

What is the reactivity series of metals? what are the trends in reactivities of metals in reactions with acids/water?

The series shows the metals in order of their reactivity.
Metals above H2 in reactivity series react with acid to produce H2. The more reactive the metal is, the quicker and more violent the reaction with acid occurs
Metals below H2 dont react with acids
Not all metals above H2 react with water - mostly group 1 and 2, aluminium is the borderline case

What is a displacement reaction?

A reaction in which a more reactive element takes the place of a less reactive element in a compound

How are unreactive metals found in the earth?

in their natural state

How can metals less reactive than carbon be extracted?

reduction with carbon - carbon displaces the metals in a metal oxide.

How are the metals more reactive than carbon extracted?

by electrolysis

What is the general equation for a reaction between metals and acids? what type of reaction is this?

metal + acid --\> salt + hydrogen - redox and displacement reaction

Which metals in the reactivity series will react with acid?

those above hydrogen

What is the general equation for a neutralisation reaction? (not ions)

base + acid --\> salt + water

What is the general equation for the reaction between metal carbonate and acids?

metal carbonate + acid --\> salt + water + carbon dioxide

What is the general equation for the reaction between metal oxides and acids?

metal oxide + acid --\> a salt + water

What is a redox reaction?

when both reduction and oxidation occur

How is a soluble salt formed?

a) React the excess acid with some insoluble chemical (e.g. metal oxide)
b) Filter off the leftovers
c) Crystallise the product

What do acids and alkalis produce in aqueous solutions?

acids - H+ ions, alkalis - OH- ions

what are bases, acids and alkalis?

Bases are compounds that neutralise acids, acids produce hydrogen ions in aqueous solutions, alkalis are soluble bases - produce hydroxide ions in aqueous solutions

What is the pH scale and what does a pH of 7 show?

The measure of acidity/alkalinity of a solution; neutral solution

State the general equation for a neutralisation reaction in a short, ionic form.

H+ + OH\- --\> H20

What is a strong acid? what is a weak acid?

Strong acid is completely ionised in aqueous solution; weak acid is only partially ionised in aqueous solution.

what happens to pH as concentration of H+ increases?

it decreases

What is a concentrated acid and what is a dilute acid? is this the same as a strong and weak acid?

- concentrated acid has more moles of acid per unit volume than dilute
- it is not the same - concentration is not the same thing as stength of an acid - strength refers to where the acid is completely ionised in water or only partially

As the pH is decreased by one unit, what change is seen in the hydrogen ion concentration?

increased by a factor of 10

What is an element?

a substance containing only one type of atom

What is an atom?

The smallest part of an element that can exist

Elements may combine through chemical reactions to form new products; what are these new substances called?

compounds

What is a compound?

two or more elements combined chemically in fixed proporrtions which can be represented by formulae

Do compouds have the same properties as their constituent elements?

no, they have different properties

What is a mixture? Does it have the same chemical properties as its consituent materials?

A mixture consists of two or more elements or compounds not chemically combined together; it does have the same chemical properties

What are the methods through whuch mixtures can be seperated (5)?

- filtration
- crystallisation
- simple distillation
- fractional distillation
- chromatography

Describe and explain simple distillation?

is used to seperate liquid from a solution - the liquid boils off and condenses in the condenser. The thermometer will read the boiling point of the pure liquid. Contrary to evapouration, the liquid is kept

Describe and explain crystallisation/evapouration

- evapouration seperates a solute from a solvent - the solvent evapourates leaving the solute
- crystallisation only removes some of the solvent by evapouration to form a saturated solution, it is then cooled forming crystals

Describe and explain fractional distillation?

Fractional distillation is a technique for separation of a mixture of liquids. It works when liquids have different boiling points.
The apparatus is similar to the one of simple distillation apparatus, with the additional fractionating column placed on top of the heated flask.
In industry, mixtures are repeatedly condensed and vapourised. The column is hot at
the bottom and cold at the top. The liquids will condense at different heights of the
column.

Describe and explain filtration?

Filtration is used to separate an insoluble solid is suspended in a liquid. The insoluble solid (called a residue) gets caught in the filter paper, because the particles are too big to fit through the holes in the paper. The filtrate is the substance that comes through the filter paper. Apparatus: filter paper + funnel.

Describe and explain chromatography

Chromatography is used to separate a mixture of substances dissolved in a solvent.
In paper chromatography, we place a piece of paper with a spot containing a mixture in a beaker with some solvent. The bottom of the paper has to be in contact with
the solvent. The solvent level will slowly start to rise, thus separating the spot (mixture) into few spots (components).

What is a separating funnel?

A device used to separate dense liquids from less dense ones

Describe the plum pudding model?

the atom is a ball of positive charge with negative electrons embedded in it

Describe the Bohr/nuclear model and how it came about

The nuclear model suggests that electrons orbit the nucleus at specific distances (shells) - it came about from the alpha scattering experiment (rutherford)

Later experiments led to the discovery of smaller, positive particles in the nucleus; what are these particles called?

protons

What did the work of James Chadwick provide evidence for?

the existence of neutrons in the nucleus

Describe the structure of an atom

The atom has a small central nucleus (made up of protons and neutrons) around which there are electrons

State the relative masses and relative charges of the proton, neutron and electron

proton: 1 , +1
neutron: 1, 0
electron: negligable, -1

Explain why atoms are electrically neutral.

They have the same number of electrons and protons

What is the radius of an atom?

0.1nm

What is the radius of the nucleus and what is it compared to that of the atom?

1 x 10^-14m and 1/10,000 of an atom

What name is given to the number of protons in the nucleus

atomic number

Atoms of the same element have the same number of which particle in the nucleus?

Protons

Where is the majority of the mass of an atom?

the nucleus

What is the mass number?

the total number of protons and neutrons

What is an isotope? Do isotopes of a certain element have the same chemical properties?

Atoms of the same element that have a different number of neutrons but the same number of protons and electrons
they have the same chemical properties as they have the same electronic structure

What is relative atomic mass?

The average mass value which takes the mass and abundance of isotopes of an element into account, on a scale where the mass of 12C is 12.

Give the electron configuration of He (2), Be(4), F(9), Na (11), Ca (20)

He- 2
Be - 2,2
F - 2,7
Na , 2,8,1
Ca - 2,8,8,2

What are ions?

Ions are charged particles that are formed when atomc lose or gain electrons

Compare the properties of metals and non-metals

Metals: High boiling and melting point, conduct heat and electricity, shiny, malleable, high density, basic oxides.
Non metals: low boiling and melting point, don't conduct heat and electricity except graphite, dull, brittle, low density, acidic oxides.

What is a solute? solvent? solution?

a solute is a solid dissolved in a liquid, a solvent is the liquid the solid is dissolved in, together they form a solution

What is miscible and immiscible?

Miscible refers to the sumstances that mix together, if something is immiscible they do not mix (oil and water)

What is soluble? insoluble?

soluble refers to the substances taht cam be dissolved in a solvent, insoluble substances won't dissolve in a particular solvent

What is formed when a metal reacts with a non-metal

An ionic compound (made of positive and negative ions)

What is formed when a non-metal reacts with a non-metal?

A moelcular compound containing covalently bonded atoms, where atoms share electrons as opposied to transferring electrons

Describe properties of fullerenes

- hollow shaped molecules
- has hexagonal carbon rings
- c60 has spherical shape (buckminsterfullerene)

Describe properties of Nanotubes

- cylindrical fullerene with high length to diameter ratio
- high tensile strength
- conductivity

What are alloys? Why are they harder than pure metals?

- mixtures of metals with other elements, usually metals
- different sizes of atoms distort the layers so they cant slide over each other

What is ionic bonding?

The electrostatic attraction between oppositely charged ions

How are ionic compounds held together?

They are held together in a giant lattice, it's a regular structure that extends in all directions in a substance and the electrostatic attraction between positive and negative ions holds the structure together.

State properties of ionic substances

- High melting and boiling point (strong electrostatic forces between
oppositely charged ions)
- Do not conduct electricity when solid (ions in fixed positions).
- Conduct when molten or dissolved in water - ions are free to move.

What is a covalent bond?

Covalent bond is a shared pair of electrons between two atoms.

Describe the structure and properties of simple molecular covalent bonds?

- do not conduct electricity
- small molecules
- weak intermolecular forces
- low melting and boiling points

How do intermolecular forces change as the mass/size of the molecule increases?

they increase

What are polymers?

Polymers are very large molecules with atoms linked by covalent bonds.

Whare are giant covalent substances?

- solids, atoms covalently bonded together in a giant lattice
- high melting and boiling point
- mostly dont conduct electrons

give examples of giant covalent substances?

Diamond, graphite, silicon dioxide

What are the properties of diamond?

- four strong covalent bonds for each carbon atom
- very hard
- very high melting point
- does not conduct electricity

What are the properties of graphite?

- three covalent bonds for each carbon atom
- layers of hexagonal rings
- high melting point
- layers free to slide as weak intermolecular forces between layers, soft, can be used as lubricant
- conduct thermal and electricity due to one delocalised electron per each carbon atom

Describe and explain the properties of fullerenes?

- hollow shaped molecules
- based on hexagonal rings but may have
5/7-carbon rings
- C60 has spherical shape, simple
molecular structure (Buckminsterfullerene)

Describe and explain the properties of nanotubes?

- cylindrical fullerene with high length to diameter ratio
- High tensile strength (strong bonds)
- Conductivity (deloc. electrons)

What is graphene?

A single layer of graphite

What is metallic bonding?

Forces of attraction between delocalised electrons and nuclei of metal ions.

Describe the properties of metals

- High melting/boiling points (strong forces of attraction)
- Good conductors of heat and electricity (delocalised electrons)
- Malleable, soft (layers of atoms can slide over each other whilst maintaining
the attraction forces)

What is the limitations of the simple particle model?

There are no forces between spheres
atoms, moleculesand ions are shown as a solid sphere - not true

What does the amount of energy needed to change state from solid to liquid or liquid to gas depend on?

The strength of the forces between of the substances. The nature of the particles involved depends on the type of bonding and the structure of the substances. The stronger the forces between the particles the higher the melting and boiling point of the substances

A pure substance will melt or boil at...? what about the mixture?

pure - a fixed temperature
mixture - over a range of temperatures

What are the three states of matter?

solid, liquid, gas

What is an exothermic reaction?

A reaction where energy is transferred to the surroundings so the temperature of the surroundings increases

Give 3 examples of exothermic reactions

combustion, oxidation, respiration

What is an endothermic reaction?

A reaction where energy is taken from the surroundings so the surroundings temperature decreases

GIve 2 examples of endothermic reactions

thermal decomposition, photosynthesis,

What is activation energy?

the minimum amount of energy needed to start a chemical reaction

What is a reaction profile?

a graph which shows the realtive energies of reactants and products, as wekk as activation of the reaction

What occurs in an endothermic reaction in terms of bond energy?

Energy needed to break the bonds is greater than energy released making them

What occurs in an exothermic reaction in terms of bond energy?

Energy released from forming bonds is greater than that needed to break the bonds

What is the equation to find the energy change in terms of bond energy?

energy change \= sum of bonds broken - sum of bonds made

What is the conservation of energy principle?

Energy is conserved in chemical reactions. The amount of energy in the universe at the end of a chemical reaction is the same as before the reaction takes place

How are the elements listed and approximately how many are there?

listed in the periodic table - approximately 100

Elements can be calssfied into two groups based on their properties; what are these groups?

metals and non-metals