1i) Electrolysis

An electric current is the flow of electrons or ions. Covalent compounds can not conduct electricity because they make bonds by sharing electrons which means that they don't have any charge carriers that are free to move.

Electrolytes are liquids that conduct electricity:

Telling the difference between electrolytes and non-electrolytes:

When you place a conductivity probe in an electrolyte, the current flows through the circuit so you can measure its conductivity. When you place a conductivity probe in a non-electrolyte, no currents flow so the reading would be zero conductivity.

Another way of determining would be setting up an electrolytic cell, if the substance will undergo electrolysis then it is an electrolyte.

Electrolysis is when an electric current is passed through an ionic substance that's molten or in solution and it breaks down into a new substance(s). It is free electrons which conduct the electricity.

Example of Electrolysis is Molten Lead (II)Bromide or PbBr₂

Ion present: Pb²⁺ and Br^-

Ion attraction to electrode:

Cathode (-) Pb²⁺

Anode (+) Br^-

Half Equations of the electrodes show what is happening at each stage:

Cathode: Pb²⁺ + 2e^- → Pb

Anode: 2Br- → Br₂ + 2e^-

Electrolysis of aqueous solutions:

As well as the ions from the ionic compound there will be hydrogen ion (H+) and hydroxide ion (OH-) from the water

At the Cathode H+ ions or metal ions (if the metal is less reactive than hydrogen) are present

At the Anode OH- ions or a halide ion when they are in the experiment are present.

Examples:

Sulfuric Acid-

Contains three ions: SO₄^2-, H+ and OH-

Cathode (-) Hydrogen gas is produced:

half equation is 2H+ + 2e^- → H₂

Anode (+) Oxygen and water is produced:

half equation is 4OH- → 2H2O + 4e-

Copper (II) Sulfate-

Contains three ions: Cu²⁺, SO₄^2-, H+ and OH-

Cathode (-) Copper metal is produced:

half equation is Cu²⁺ +2e^- → Cu

Anode (+) Oxygen and water is produced:

half equation is 4OH^- → 2H₂O + 4e^-

Coulombs and Faradays are amounts of electricity:

• one amp flowing for a second means a charge of one coloumb has moved
• Q (charge) = I (Current) x t (Time)
• 96000 coulombs is called one faraday
• One faraday (F) contains one mole of electrons

1e) Chemical Formulae and Chemical Equations

Word equations and Balanced chemical equations are used to represent the reactions studied in this specification. In a chemical equation you have to use state symbols: (s), (l), (g) and (aq) in chemical equations to represent solids, liquids, gases and aqueous solutions

Water of Crystallisation:

• solid salt with water is HYDRATED
• salt without water is ANHYDROUS
• calculate it by:

1. Working out the mass
2. Number of moles of water lost
3. ratio of anhydrous salt made
4. ratio of anhydrous to mole of Water
5. X must be a whole number

Empirical formula:

Is the simplest formula that tells you the ratio of different elements in the compound

1. List all the elements in the compound
2. Write underneath the experimental masses/ percentage
3. Divide by A_r of elements
4. Change to simple ratio by multiplying and/or dividing them by well chosen numbers
5. Simplify ratio

Molecular Formula:

A compound tells you the actual number of atoms each element in a single molecule

Calculate Masses in Reactions:

1. Write out the balanced equation
2. Work out the and multiply them by balancing numbers in the equation
3. Apply the rule: Divide to get one, then multiply to get all

Percentage Yield:

= (mass obtained/ mass predicted) x 100

Moles and Concentration

Concentration = Number of Moles / Volume

1d) Relative formula masses and molar of gases

Relative formula mass can be found by adding up the mass numbers

A mole is a precise number. When you get precisely that number of atoms or molecules, of any element or compound, they weight exactly the same number of grams as the relative atomic mass, A_r of the element or compound. One mole of atoms or molecules of any substance will have a mass in grams equal to the relative formula mass for that substance.

Example- Carbon has an A_r of 12 and so the one mole of carbon weighs exactly 12g.

The number 6.023x10²³ is called Avogadro's number or the Avogardo constant. So you can think of a mole as the Avogardo number of particles in a substance, where the articles are atoms, molecules, ions or electrons.

Number of moles = Mass in g/ M_r

One mole of any gas always occupies 24dmº (=24000 cmº) at room temperature and pressure (RTP: 25ºc and 1 atmosphere)

Volume (dm³) = moles of gas x 24

Volume (dm³) = (mass of gas/ M_r of gas) x 24

5c) Synthetic Polymers

A Monomer is a single molecule that join together to make a polymer
Polymers are long chain molecules made from monomers

Addition Polymers:

Uses of polymers:
Poly(ethene)- plastic bags and bottles
Poly(propene)- crates  and ropes
Poly(chloroethene)- water pipes and insulation on electricity cables

Disposal of addition polymers:
They are non-biodegradable because of their strong single bonds- inert
Some compounds are toxic if inhaled
They have to be put in land fills which occupy a lot of land in the UK, they can also be recycled or incinerated

Paper Two- Condensation Polymers: 

Made from two different monomers and have atoms other than C (carbon) in main chain. These polymers also form small molecule as well as a polymer, usually H2O or HCl. 

 

3d) Ethanol

This whole section is for Paper Two:

Manufacture of Ethanol by Ethene and Steam (H₂O):  

-C₂H₄ + H₂O  C₂H₅OH
-hydration- exothermic
-300C and 60-70 atm
-phosphoric acid catalyst
-un-reacted ethene recycled

fast reaction 
pure ethanol
continuous 

non-renewable resources 
energy needed to make steam 

Manufacture of Ethanol from Fertilisation: 

-C₆H₁₂O₆ -----> 2C₂H₅OH + 2CO₂
-anaerobic respiration
-exothermic reaction
-20-60 hrs

-30-40C
-purified by fractional distillation

renewable resources 
organic waste material 

impure ethanol due to water 
slow process
only 15% ethanol in each batch 

Dehydration of Ethanol to Ethene:

Ethanol    ------> Water and Ethene 

C₂H₅OH ------>  H₂O  and C₂H4 

1f) Ionic compounds + 1g) covalent compounds

Ionic bonding:

• strong electrostatic attraction 
• opposite charged ions 
• throughout lattice 

Properties of ionic compounds:

• high melting point 
• strong electrostatic attraction 
• giant ionic lattice 
• soluble in water 
• Ions attracted to polar water molecules 
• conduct electricity 
• ions can move and carry charge

A Lattice is a 3-D network of ions in fixed positions bonded together 

OIL RIG 

Oxidation- loses electrons                      Reduction- gains electrons 

Group	1	2	3	4	5	6	7	0/8
Charge	1+	2+	3+	X	3-	2-	1-	X

Covalent bonding:

• non metal with non metal 
• outer shells overlap 
• electron shared in pairs 
• atoms achieve outer shells (full)
• attracts both nuclei 

Properties of simple covalent molecules:

• very strong bonds
• low melting and boiling points 
• insoluble in water 
• no free electrons 
• Don't conduct electricity 
• soluble in organ solvents 

Intermolecular forces 

• weak bonds
• easily broken 

Giant covalent bonds 

• strong bonds 
• no free electrons 
• rigid 
• all atoms joined together 
• covalent unreactive 

Diamonds 

• rigid 
• hard 
• sparkly
• four covalent bonds  

Graphite

• layers three covalent bonds 
• slide over each other 
• free electrons 
• good conductor of electricity 
• lubricant