1.57 calculate the amounts of the products of the electrolysis of molten salts and aqueous solutions.

CALCULATIONS:

- If 2.5 amps are passing through sodium chloride for 15 minutes. What mass of sodium do we get?

- 1. Write out the half-equation:
2H+ + 2e- -> H2

- Calculate number of faradays.
Q = IxT
Q = 2.5 x (15 x 60 = 900) = 2250 coulombs.
Faradays = Q / FQ
Faradays = 2250 / 96000 = 0.0234375 F

- Calculate number of moles of sodium produced.
Moles = Faradays / (Electrons in half-equation)
0.0234375 / 2 = 0.01171875 moles of sodium atoms.

- Calculate Mr to workout mass.
Mass of sodium = Mr x Moles
23 x 0.01171875 = 0.26953125 = 0.27 g

For better equations go to: (http://www.docbrown.info/page04/4_73calcs13pec.htm)

1.56 recall that one faraday represents one mole of electrons

FARADAYS:

- A faraday is the same as 96,485.3365 coulombs but for the exam you are allowed to know it as 96,000 coulombs.
- One faraday also contains one mole of electrons.

1.55 write ionic half-equations representing the reactions at the electrodes during electrolysis

IONIC HALF-EQUATIONS:

- At the positive electrode, also known as the anode, electrons are lost.
2Br- -> Br2 + 2e-

- At the negative electrode, also known as the cathode, electrons are gained.
Pb^2+ + 2e- -> Pb

As http://hannahhelpchemistry.blogspot.co.uk/ has said:
- At the anode the half-equation should be equal on both sides: 1- -> 1-.
- At the cathode the half-equation should be equal on both sides: 0 -> 0.

1.54 describe experiments to investigate electrolysis, using inert electrodes, of aqueous solutions such as sodium chloride, copper(II) sulfate and dilute sulfuric acid and predict the products

SODIUM CHLORIDE:

- Place electrodes into solution, then at the anode, negatives will form and vice versa with the cathode.

- NaCl contains Na+, Cl-, OH- and H+
Hydrogen is easier to accept electrons and therefore at the cathode hydrogen gas is produced.
Chloride is easier to lose electrons than hydroxide and so chlorine gas is produced.

- CuSO4 contains Cu2+, SO4^2-, H+ and OH
Copper accepts electrons easier that hydrogen so copper is produced at the cathode.
Hydroxide loses electrons easier so at the anode oxygen and water are produced.

- H2SO4 contains SO4^2-, H+ and OH-
Hydrogen accepts electrons so at the cathode hydrogen is produced.
Hydroxide loses electrons easier than sulfate and so at the anode oxygen and water are produced.

1.53 describe experiments to investigate electrolysis, using inert electrodes, of molten salts such as lead(II) bromide and predict the products

INVESTIGATING ELECTROLYSIS:

- Inert means that they do not react with anything.
- An example of this is with lead(II) bromide. With this you can write half-equations to show the transitions of the electrons at each electrode.

1.52 understand that electrolysis involves the formation of new substances when ionic compounds conduct electricity

ELECTROLYSIS:

- Is mainly used to create new substances. In electrolysis the positive ions move to a cathode (since opposites attract) and vice versa with the negative ions. This means that the ions lose their charge and become atoms again to form new substances.

1.51 describe experiments to distinguish between electrolytes and nonelectrolytes

DISTINGUISH DIFFERENCES:

- Create a circuit that has a break in. In the circuit you should have a component that indicates a full circuit. For example a motor or LED. Place the two brakes into the dissolved or molten substance and if it is an electrolyte the component will indicate. This is because the substance conducts.

1.50 understand why ionic compounds conduct electricity only when molten or in solution

ONLY IN MOLTEN:

- The compounds are held together in a lattice (+ive and -ive ions).
- In a solid, the ions can't move around. This therefore means that when the compounds either melt or dissolve the ions are free to move again and are able to conduct electricity.

1.49 understand why covalent compounds do not conduct electricity

COVALENTS DON'T CONDUCT:

- They don't contain any ions as they only make bonds by sharing electrons. Therefore there are no charge carriers to flow around.

1.48 understand that an electric current is a flow of electrons or ions

ELECTRIC CURRENT:

- An electric current can flow from either electrons (negative charge) or ions (negative or positive charge).

1.47 explain the electrical conductivity and malleability of a metal in terms of its structure and bonding.

CONDUCTIVITY AND MALLEABILITY:


- Metals contain a sea of delocalised electrons (electrons and ions can be charge carriers). That is to say there can be a flow of electricity through the electrons and ions.
- Metals are in layers.  This means they can slide over each other and change their shape. This is called malleability.

1.46 understand that a metal can be described as a giant structure of positive ions surrounded by a sea of delocalised electrons

METALS:

- Metals are simply just 3D (three dimensional) structures which are positive ions, surrounded by a sea of delocalised electrons. A metallic bond then forms - +ive ion and -ive ions attracts.

1.45 explain how the uses of diamond and graphite depend on their structures, limited to graphite as a lubricant and diamond in cutting.

THE USES:

- Diamond can be used for cutting since each carbon atom forms four covalent bonds in a giant covalent structure; this means that it is very hard and is the hardest natural substance.

- Graphite is great for a lubricant since each carbon atom only forms three covalent bonds. This means that there are layers, which are free to slide over each other.

1.44 draw diagrams representing the positions of the atoms in diamond and graphite

DIAGRAM REPRESENTING POSITIONS:

1.43 explain the high melting and boiling points of substances with giant covalent structures in terms of the breaking of many strong covalent bonds

GIANT COVALENT STRUCTURES:

- A giant covalent structure is formed when all atoms are bonded together. There are lots of bonds and hence require a lot of energy to overcome which means that the structures have very high melting and boiling points.
- Examples are diamond and graphite.

1.42 explain why substances with simple molecular structures have low melting and boiling points in terms of the relatively weak forces between the molecules

WHY THEY ARE WEAK:

- The simple molecular structures lack strength, that is to say the molecules can me separated with very little energy.

- There are also very little intermolecular forces and so increase how easy it is to separate them.

1.41 understand that substances with simple molecular structures are gases or liquids, or solids with low melting points

SIMPLE MOLECULAR STRUCTURES:

- Held together by very strong covalent bonds. However the forces of attraction are very weak; they have low melting and boiling points.
- Examples of simple molecular structures are: chlorine, oxygen, water and iodine.

1.40 explain, using dot and cross diagrams, the formation of covalent compounds by electron sharing for the following substances: i hydrogen ii chlorine iii hydrogen chloride iv water v methane vi ammonia vii oxygen viii nitrogen ix carbon dioxide x ethane xi ethene

DOT AND CROSS DIAGRAMS:

- To successfully draw these diagrams you need to draw the outer shell electrons of the atoms involved overlapping one another. Then in the middle you draw the electrons that are shared.

- For example:
HCl

NH3

1.39 understand covalent bonding as a strong attraction between the bonding pair of electrons and the nuclei of the atoms involved in the bond

Same as 1.38

COVALENT BOND:

- Is a strong attraction between the bonding pair of electrons and the nuclei of the atoms involved.

1.38 describe the formation of a covalent bond by the sharing of a pair of electrons between two atoms

COVALENT BOND:

- Is a strong attraction between the bonding pair of electrons and the nuclei of the atoms involved.