GCSE Chemistry C2 topic notes

Salts and Electrolysis Topic Notes Neutralisation Reaction: An Acid always contains an H  ion An Alkali always contains an OH  ion A Neutralisation reaction is: As well as water, a salt is produced in a Neutralisation Reaction. Acid + Metal = Salt + Hydrogen Acid + Carbonate = Salt + Water + Carbon Dioxide Acid + Metal Oxide = Salt + Water If Acid is: HCl = Chloride Salt so the ending is Chloride H  SO  = Sulphate Salt so the ending is Sulphate HNO  = Nitrate Salt so the ending is Nitrate Soluble salts (salt that can be dissolved) can be made by: Metals – Some e.g. Na and K are too reactive, others e.eg. Au are too unreactive and so can’t be added direct. Insoluble Bases – the base is added to the acid until no more will react and then the excess solid is filtered off. E.g. insoluble base = oxides of transition metals such as iron oxide( Fe O ) Alkalis – an indicator is used to show when the acid and alkali have reacted to produce a salt solution.   Making Insoluble Salts from Solutions: Making Soluble Salt (CuSO ): Insoluble Base + Acid = Soluble Salt and Water Same for any insoluble Base e.g. MgO Only practical that you need to know the method Making insoluble salts: A precipitate is the formation of an insoluble salt. KI + Pb (NO )  = KNO  + PbI We filtered the product: To islolate the PbI  we could have washed and dried the salt This gets rid of any excess KNO . Practical use for Precipitation: Remove pollutant metal ions from the waste water of a factory. Make an Insoluble Metal Hydroxide E.g. Pb(OH)  precipitate out. This forms a sludge that can be separated from water. Ammonium Salts: Nitric Acid + Ammonia Hydroxide = Ammonium Nitrate Ammonium salts are made in neutralisation reaction They have a lot of Nitrogen that is needed for plants to grow Hence ammonium nitrate is used as a fertiliser All sodium and nitrates are soluble.

Rates of Reactions Topic Notes Fast and Slow Reactions: The Rate of a Reaction is the time it takes for the reactant to change into the product. Things that affect the rate of a reaction: Temperature Concentration Surface Area Catalyst Collision Theory: The effect of certain conditions on the rate of reaction can be explained by the collision theory between particles. For two particles to react: They must collide Must have enough activation energy Activation Energy = Minimum Energy needed for a Successful Collision Temperature: Particles have more energy so are more collisions. So a faster rate of reaction. Heating up the Chemicals and Particles Particles are hotter so have more Energy Particles get more Energy and move Faster Particles move faster and have more collisions Faster Rate of Reaction Also: More particles have the activation energy (minimum energy for an successful collision) So more successful collisions because the particles don’t need as much energy to react Faster Rate of Reaction Concentration/Pressure: There are more particles so there will be more collisions. So a faster rate of reaction. Increasing the Concentration of the Particles More particles in the same Volume of Solution Greater chance of particles colliding in the solution and therefore more collisions Increased Rate of Reaction The concentration of a solution tells us how many particles have been dissolved in a certain volume. The Unit of Concentration is mol/dm  (moles per dm ). Surface Area: There are more particles exposed so there will be more collisions. So a faster rate of reaction. Split up the pieces – Increase Surface Area More area exposed – Greater Surface Area More Surfaces exposed – so more particles can collide Greater chance of particles colliding than in a lump of solid Faster Rate of Reaction Catalyst: Catalyst = Speeds up the rate of a reaction but remains chemically unchanged at the end of the reaction A Catalyst works by offering an alternative pathway of lower activation energy. Adding a Catalyst to Increase the Rate of the Reaction The Particles do not need as much Energy to React Particles React more easily as more of the particles have enough energy to react. Catalysts are important for industry: Products are made more quickly Catalysts can reduce the need for high temperatures

Energy of Reactions Topic Notes Energy and Reversible Reactions: Equilibrium: When the reactants are making the products at the same rate as the product are making the reactants. Reversible Reactions: Where the reactants make the product and the products make the reactants. In a Reversible Reaction one way is always endothermic and the other is exothermic. It is the same value of energy taken in and released. Exothermic Reaction – Transfers energy to the surroundings. E.g. Combustion, oxidation reactions and neutralisation. Endothermic Reaction – Takes energy from the surroundings. E.g. thermal decomposition Breaking Bonds = always endothermic (E.g. Photosynthesis) Making Bonds = always exothermic (E.g. Respiration) Whether a reaction is endothermic or exothermic overall depends on the energy values for the bond breaking and making. If Exothermic Overall: Making bonds is greater than breaking bonds If Endothermic Overall: breaking bonds is greater than making bonds

Electrolysis Topic Notes Electrolysis means splitting up using electricity. Using Electricity to break down a substance. An electrolyte is the substance that is broken down by electrolysis. OIL RIG: Gaining electrons is called Reduction and losing electrons is called Oxidation. Oxidation Is Loss, Reduction Is Gain The Electrolysis of Molten Lead Bromide: Electricity is passed through molten lead bromide. The positively charged ions move to the negative electrode during electrolysis. They receive electrons and are reduced. Here molten lead is produced. Negatively charged ions move to the positive electrode during electrolysis. They lose electrons and are oxidised. Bromine gas is produced. Lead Bromide -> Lead + Bromine Electrolysis of CuCl : The negative (chloride) ions go to the Positive electrode, lose electrons and form Chlorine gas. The positive (copper) ions go to the Negative electrode, gain electrons and form Copper. Copper is formed at the negative electrode and Chlorine gas is formed at the positive electrode. You can test for Chlorine gas because it will turn litmus paper red because it’s acidic. Aluminium: Aluminium is a reactive metal that has a low density but is strong. Aluminium ore is a bauxite Aluminium Bauxite is mixed with Cryolite to lower the melting point from 2500 → 850℃ It has to be molten for the ions to move. The high temperatures mean that a lot of energy is required so the plant will have its own power station. Extraction of Aluminium: Negative Electrode – Positive Al atoms are attracted to the negative electrode. They gain electrons and are reduced to form aluminium (atoms). Positive Electrode – Negative O  ions are attracted to the positive electrode. They lose electrons and are oxidised to form Oxygen. This reacts with the carbon electrode to form Carbon dioxide. Electrolysis of Brine: Molten NaCl produces Na  + Cl  ions NaCl solution (brine) produces Na  + Cl  + H  + OH When we electrolyse brine, the products depend on their reactivity. The more reactive ions stay in the solution. Na  + OH  →NaOH (alkaline turns universal indicator blue/ red litmus blue) +ve electrode 2Cl  -2e  → Cl –ve electrode 2H  + 2e  → H Uses: Chlorine = Disinfectant in swimming pool Hydrogen = Rocket Fuel Sodium Hydroxide = bleach What happens in the electrolysis of Brine? NaCl(aq) → Na  + Cl  + H  + OH Positive Electrode: The negative chloride ions are attracted to the positive electrode (anode). They lose electrons It Oxidises to form Chlorine Gas (molecules) 2Cl (aq) – 2e  → Cl (g) Negative electrode: The positive Sodium ions are attracted to the negative electrode (cathode). They gain electrons It reduces to form Sodium (atoms). Na  + e  → Na(s) An electrolyte is a substance that is broken down by electrolysis. Test for Chlorine: Red litmus paper → blue Test for Hydrogen: The pop test. Lit splint → pop Electroplating: At the negative electrode – Copper ions gain electrons (reduction) to form Copper metal. Cu   + 2e  → Cu At the positive electrode – Copper strip loses electrons (oxidisation) to form Copper ions. The positive electrode dissolves Cu – 2e  → Cu  Electroplating is useful because we can plate items to make them look nicer and its cheaper than using pure metal. Copper plating: Negative Electrode – Copper goes to the Negative electrode because they are positive ions. They gain 2 electrons and are reduced. This makes a layer of Copper on the nail.                    Cu   + 2e  → Cu Positive Electrode – Sulphate stays in solution. (The solution is losing copper ions and it wants them back. This is because the positive electrode is being dissolved). The copper atoms at the copper electrode lose electrons, they are oxidised. This forms copper ions which go back into the solution. Cu – 2e  → Cu  The concentration of the solution stays the same because the copper is lost at the same time it is gained. It is losing/ gaining electrons at a steady rate.

Structure and Bonding Topic Notes Atomic Structure: Mass number is the number of protons and neutrons. It is all the mass in the Nucleus. Atomic number is the number of protons. For an atom only, this is the same as electrons. Protons: atomic number Electrons: Atomic number Neutrons: Mass number – atomic number Electrons: The number of electrons in the outer shell tells us the group number for that element. Isotopes: Almost all elements have isotopes. E.g. Carbon    C p=6 n= 6 e = 6 Carbon has two other isotopes:   C 13 C 14 Protons 6 6 Neutrons 7 8 Electrons 6 6 Table to show the differences between isotopes: Same Different Proton Number Neutron Number Electron Number Mass Number Atomic number Unstable Charge of the atom Physical properties Chemical Properties   Carbon Dating: The trees and plants take in Carbon 12 +14 through photosynthesis. Humans and animals take in the carbon when eating the plants. They die and the carbon levels no longer increase. C12 stays constant, however C14 decays, giving out radiation. They measure the ratio between C14 and C12 levels to identify the age of the object. Every time it decays there is half as much carbon. This is a half life. Ionic Bonding: Between a metal and a non-metal To gain a full outer shell Involves the loss and gain of electrons to form ions. It is not and actual bond but is: A strong electrostatic attraction Between all oppositely charged ions in a giant lattice Properties: High melting point – need a lot of energy to break the electrostatic attraction. High boiling point Only conducts when molten or in a solution – because the ions are free to move and carry the charge Lithium loses and electron to gain a full outer shell. Lithium becomes a +1 ion. Fluorine gains an electron to gain a full outer shell. Fluorine becomes a -1 ion. Covalent Bonding: Between two non-metals Involves the sharing of electrons A Covalent Bond is a shared pair of e  (electrons) Covalent Compounds form 2 types of molecules: Simple Molecular E.g. HCl, H O, CH , NH Simple molecules have low boiling/ melting points because: The weak intermolecular forces are broken. Not the strong covalent bonds. Not much energy is required. Giant Covalent Only examples you need to know are diamond (C), graphite (C), silicon dioxide (SiO ) These structures only have strong covalent bonds. Diamond: Diamond has a very high melting/ boiling point Graphite: It has a delocalised e  between the layers of Carbon atoms. This means: It can conduct electricity The layers can be separated because it is soft Fullerenes are used as lubricants because the layers slide past each other with no covalent bonds formed.

SAlts and electrolysis

Rates of reactions

Energy of reactions

Electrolysis

Structure and bonding