Extension Science Chemistry C3Revision

C3.1 Water Testing Qualitative Analysis is where you find out what type of substance you have present. Quantitative Analysis is when you deduce the amount of unknown sample you have. Water samples contain IONIC COMPOUNDS which contain both CATIONS (positive) and ANIONS (negative ions). Ion tests must only give a positive result or one type of ion.

C3.1 Water Testing Flame tests are commonly used for CATION (metals). Precipitate reactions can also be used by reaction the ionic solution with SODIUM HYDROXIDE as most metal hydroxides are insoluble in water.

C3.2 Safe Water Testing for the Halogens This is performed by acidifying the sample with dilute Nitric Acid and then reacting with Silver Nitrate to form a precipitate. This reaction works by the Halogen displacing the Nitrate in Silver Nitrate with the Halogen. Testing for Ammonium ions (NH4+) Warm the solution to release the Ammonium ions as a vapour It will turn damp red litmus paper blue.

C3.3 Ion Identification Imagine you have been given an unknown sample…how can you test for the different Ions. 1) 2) 3) 4)

C3.4 Safe Limits Ion identification is used in many different industries. For example: Water Industry to test for dissolved ions (both Halogens and other ions such as aluminium (linked to Alzheimer's disease). Blood testing to test for different ions (Iron linked to Anaemia, Sodium linked to kidney function).

C3.5 Water Solutes Types of Water Soft water – contains low levels of ions (Na, Mg) – easily produces a lather Hard water – contains lots of dissolved ions (Ca, Mg) – produced scum not lather – used lots of soap for cleaning Permanently hard water – cannot be easily softened Temporarily hard water – can be softened by boiling.

Calculating Concentration C3.5 Water Solutes Calculating Concentration Concentrations of ions are calculated generally in mgdm-3 or gdm-3. 1dm3 is equal to 1000cm3 (1 litre) To calculate concentration use the following formula:

Temporarily hard water C3.6 Hard and Soft Water Temporarily hard water This water is softened by boiling. It converts the Calcium Hydrogen carbonate into insoluble Calcium Carbonate (lime scale). Softening the water improves its ability to form a lather and therefore reduce the amount of soap required.

Softening Permanently hard water C3.6 Hard and Soft Water Softening Permanently hard water This can be performed using ION EXCHANGE. This involves Sodium ions (Na+) in the resin displacing Calcium (Ca2+) and Magnesium (Mg2+) in the water sample and softening it.

C3.7 Finding the mass of a solute in a solvent

C3.8 Particles and Moles Substances can be measured in several ways. They can be: Number of grams Number of particles Number of moles One mole of atoms is equal to the AVEGADRO number of particles (6.02X1023) The mass of one mole of atoms is equal to the Relative Atomic Mass number (top number on periodic table).

C3.8 Particles and Moles To calculate the number of moles use the following formulas:

C3.9 Preparing Soluble Salts Making Copper Sulphate from Copper Oxide React excess oxide (insoluble) with accurate volume acid. Filter excess copper oxide and collect copper sulphate solution. Evaporate solvent (water) to crystallise the salt.

C3.9 Preparing Soluble Salts Titrations (preparing a salt from two soluble reactants) These reactions are NEUTRALISATION REACTIONS. It involves accurately calculating the volume of ACID required to neutralise the BASE. An INDICATOR is used to deduce the point of NEUTRALISATION (end point). A pipette is used to measure the base accurately. A burette is used to add the acid accurately. One the correct volumes have been obtained then the reaction is performed without the indicator

C3.9 Preparing Soluble Salts

C3.11 Acid Alkali Titrations

C3.12 Titrations and Calculation Calculate number of moles of acid used. Write balanced equation for reaction. Using moles of acid information, deduce number of moles of base required. Calculate concentration of base. This process also works the same in reverse.

C3.13 Electrolysis Electrolysis can only happen when IONIC substances are either DISSOLVED or MOLTEN. Sodium metal is produced through the electrolysis of MOLTEN Sodium Chloride.

C3.13 Electrolysis Oxidation is the loss of electrons and happens at the ANODE. Reduction is the gain of electrons and happens at the CATHODE. Sodium metal is used in street lights as it gives out a yellow coloured light. Liquid Sodium is used as a coolant in Nuclear Reactors as it has a high THERMAL CONDUCTIVITY.

C3.14 Electrolysis of Sodium Chloride

C3.15 Electrolysis of Salts When you perform the electrolysis of a molten salt you produce ions that are discharged as atoms or molecules. For example, when you perform the electrolysis of Lead Bromide Pb(II)Br2 you obtain both Lead and Bromine gas.

C3.15 Electrolysis of Salts Electrolysis of salts in solution This involves both the electrolysis of the salt and the electrolysis of water. The salt splits into its two component ions. The water splits into Hydrogen ions (H+) and Hydroxide Ions (OH-). To perform electrolysis you must have INERT (unreactive) electrodes as some of the products can be highly corrosive.

Electrolysis of Sodium Chloride Solution

C3.16 Investigating the electrolysis of Copper Sulphate

C3.17 Uses of Electrolysis Purification of Copper An electrode of impure copper is used as the ANODE. Pure copper is used as the CATHODE. The electrolyte is Copper Sulphate solution.

C3.17 Uses of Electrolysis Electroplating Electroplating is when a thin coat of valuable (or unreactive) metal is applied to a cheaper (more reactive) metal. Silver and Gold are metals that are commonly used for electroplating.

C3.18 Molar Volume of Gases 1 mole of = 24dm3 (at room temperature and a gas atmospheric pressure) A GAS SYRINGE is used to collect gases during reactions to allow molar gas calculations to be performed

C3.19 Fertilisers and the Haber Process Nitrogenous fertilisers (ones that contain Nitrogen) are manufactured from AMMONIA. These fertilisers are used to promote plant growth. These fertilisers increase the yield of crops that are produced. If these fertilisers are used excessively then this can lead to run off into rivers and lakes (or any other water source). This results in excessive plant growth (EUTROPHICATION). When these plants die they decompose by bacteria which uses up the OXYGEN.

C3.19 Fertilisers and the Haber Process The HABER process is a REVERSIBLE reaction which will reach DYNAMIC EQUILLIBRIUM. Dynamic equilibrium is where the FORWARDS and BACKWARDS reactions are happening at the same rate.

C3.20 The Haber process When AMMONIA is formed it releases heat (EXOTHERMIC). This is the FORWARDS reaction. The reverse reaction will be the opposite which makes it ENDOTHERMIC (takes in heat) When DYNAMIC EQUILLIBRIUM is reached these two reactions occur at the SAME RATE. Adjusting the temperature and pressure will affect the position of the equilibrium, favour the PRODUCT or REACTANT.

C3.20 The Haber process N2 + 3 H2 ⇌ 2 NH3 Reactant = 4 molecules Products = 2 molecules Pressure and the Haber process If you increased the pressure of the reaction the equilibrium would favour the PRODUCTS (move to the right). This is because the particles are being forced closer together and therefore more likely to react. Temperature and the Haber process As the reaction is EXOTHERMIC it favours cooler conditions (it releases energy into the surrounding environment). An increase in temperature would move the equilibrium to the left (favour the reactants). A low temperature would increase the yield but slow the rate of reaction.

C3.20 The Haber process Optimal conditions are used to ensure that the maximum possible yield is produced safely and at a sufficient rate to be economically viable. Temperature – approx. 450OC Pressure – 200atm (200 times atmospheric) Catalyst – Iron catalyst A catalyst increases the rate of reaction without ever being used in the reaction. It works by lowering the activation energy for the reaction (energy required for a successful collision) If the temperature or pressure is too high then there can be safety implications and too low will result in a lower yield.

C3.21 Fermentation Ethanol (alcohol) can be produced by the fermentation of CARBOHYDRATES (sugars). Fermentation occurs when YEAST convert sugars into alcohol. The yeast act as an ENZYME. For this to happen successfully the following conditions must be sustained: Kept warm (allow the bacteria to work successfully, too hot will kill them) Anaerobic conditions (no oxygen)

C3.22 Alcoholic Drinks Different types of alcoholic drink contain different percentages of ethanol. The higher the alcohol content the higher % it is given. 1 unit of alcohol = 10cm3 pure ethanol The effects of alcohol are: Slower reaction times Violent/aggressive behaviour Loss of balance/coordination Vomiting and fainting Dehydration Prolonged alcohol consumption can result in an increased risk of HEART DISEASE, STROKE or LIVER CIRROHISIS. Alcoholic spirits are made by FRACTINAL DISTILLATION where the ethanol is removed first and the water is left behind (increasing the alcoholic content)

C3.23 Ethanol production Ethanol can be produced in two main ways: 1. Fermentation – sugars are turned into ethanol and carbon dioxide through the anaerobic respiration of YEAST. 2. Hydration of Ethene (crude oil fraction) – reacting ethene with steam in the presence of a catalyst (addition reaction)

C3.23 Ethanol production Each method of Ethanol production has both social, environmental and economical advantages and disadvantages. This information needs to be evaluated to determine the best method of production for individual cases. Making Ethene Ethene can be made by the cracking of CRUDE OIL but also the DEHYDRATION of Ethanol.

C3.24 Homologous series Alkanes – a hydrocarbon containing only A HOMOLOGOUS series is a series of compounds that have the same general formula and similar chemical properties but have variation in boiling points. Alkanes – a hydrocarbon containing only C-C bonds. Alkenes – a hydrocarbon containing at least one C=C bond. Alcohol – a hydrocarbon containing at least one –O-H group.

C3.24 Homologous series

C3.25 Ethanoic acid Ethanoic acid is a CARBOXYLIC ACID. It is the active ingredient in VINEGAR. It is produced by the OXIDATION of ethanol (under aerobic conditions). It has a sharp, sour taste and can be used as a PRESERVATIVE. Ethanoic acid reacts with metals to form salts (ending – ethanoate). Carboxylic acids react in the same way as normal acids. They are classified as weak acids. Carboxylic acids are named in the same way as other homologous series. Their ending is –anoic acid. Their functional group is –COOH.

C3.26 Esters Esters are made during the reaction of ALCOHOLS and CARBOXYLIC ACIDS. They are commonly used as FLAVOURINGS and FRAGRANCES as they have distinctive smells and tastes. Ethanol reacts with ethanoic acid to from the ester ETHYL ETHANOATE. Esters can also be turned into FIBRES to make FABRICS – POLYESTER. Polyesters can be recycled to form FLEECE.

C3.27 Fats, Oils and Soaps Fats and Oils are big esters. The only difference is fats are SOLID at room temperature where as oils are LIQUID. Soaps can be made from fats and oils by heating with a concentrated alkali. Oils are commonly UNSATURATED (contain C=C bonds). Fats are SATURATED (contain C-C bonds). To turn an oil into a fat you must HYDROGENATE it (addition of Hydrogen)

C3.27 Fats, Oils and Soaps How do Soaps work? A soap can be shown as a tadpole shape – head is water loving (HYROPHILLIC) and tail is water hating (HYDROPHOBIC). The head has a negatively charged oxygen ion (anion). The tail is a hydrocarbon (water hating) Hydrophobic tail sticks into grease. Hydrophilic end sticks out to attract water. Grease particle surrounded by hydrophilic heads. Removed by water attraction (grease can now mix with water)