AQA GCSE Chemistry

AQA GCSE Chemistry What is the charge of a proton? - ANS +1 What is the charge of a neutron? - ANS 0 What is the charge of an electron? - ANS -1 What is the relative mass of a proton? - ANS 1 What is the relative mass of a neutron? - ANS 1 What is the relative mass of an electron? - ANS Very small How many types of atoms do elements contain? - ANS Only one type What are compounds? - ANS Substances containing two or more different elements that are chemically bonded together What are mixtures? - ANS Substances containing two or more different elements that are not chemically bonded together What pattern is formed from carrying out paper chromatography? - ANS Chromatogram Which method of separation is useful to separate an insoluble solid from a liquid? - ANS Filtration Which method of separation is useful to separate a soluble solid from a liquid? - ANS Evaporation or Crystillisation Which method of distillation separates liquids with similar boiling points? - ANS Fractional distillation Who discovered that the plum pudding model was wrong? - ANS Ernest Rutherford Who devised an experiment that proved the existence of the neutron? - ANS Niels Bohr Why did Mendeleev leave gaps in his Table of Elements? - ANS To ensure that elements with similar properties stayed in the same groups. The gaps indicated the existence of undiscovered elements and allowed Mendeleev to predict what their properties might be How are the group number and the number of electrons in the outer shell of an element related? - ANS The group number tells you how many electrons are in the outer shell of an element. E.g. sodium is in Group 1 therefore it has 1 electron on its outer shell What kind of ions do metals form? - ANS Positive Where are the non-metals on the periodic table? - ANS On the right hand side Give three properties which are specific to transition metals - ANS 1) They can form more than one ion e.g cobalt form Co2+ 2) They are often coloured, therefore compounds which contain them are colourful e.g. potassium chromate is yellow 3) They often make good catalysts e.g. nickel based catalysts are used in the hydrogenation of alkenes State three trends as you go down Group 1 - ANS 1) Increased reactivity - the outer electron is more easily lost as the attraction between the nucleus and the electron decreases because the electron is further away from the nucleus 2) Lower melting and boiling points 3) Higher relative atomic mass What are the products of the reaction of a Group 1 metal and water - ANS Hydrogen gas and a metal hydroxide E.g. sodium + water -- sodium hydroxide + hydrogen What's the difference between the hardness of Group 1 and transition metals? - ANS Transition metals are harder, denser and stronger than Group 1 metals What's the difference between the reactivity of Group 1 and transition metals? - ANS Group 1 metals are much more reactive than transition metals What's the difference between the melting points of Group 1 and transition metals? - ANS Transition metals have higher melting points than Group 1 metals What trends occur as you go down Group 7? - ANS 1) They become less reactive - it's harder to gain an extra electron because the outer shell's further from the nucleus 2) They have higher melting and boiling points 3) They have higher relative atomic masses What is the charge of the ions that halogens form when they react with metals? - ANS They form negative ions What is the trend in boiling point as you go down Group 0? - ANS The boiling points increase What subatomic particles does the nucleus contain? - ANS Protons and neutrons What is relative atomic mass? - ANS The mass number which refers to the element as a whole How are positive ions formed? - ANS A metal atom loses electrons How are negative ions formed? - ANS A non-metal gains electrons What is air a mixture of? - ANS Gases, mainly nitrogen, oxygen, carbon dioxide and argon What is crude oil a mixture of? - ANS Different length hydrocarbon molecules How can you separate substances in a mixture? - ANS Chromatography What is simple distillation used for? - ANS Separating out a liquid from a solution E.g. separating pure water from seawater How were elements arranged in the early 1800s? - ANS By their physical and chemical properties and their relative atomic mass How are columns arranged? - ANS Elements with similar properties What are the three similar basic properties of metals? - ANS 1) They're strong but are malleable 2) They're great at conducting heat and electricity 3) They have high boiling and melting points What is the product of the reaction of a Group 1 metal with chlorine? - ANS A metal chloride salt E.g. sodium + chlorine -- sodium chloride What is the product of the reaction of a Group 1 metal with oxygen? - ANS A metal oxide, depending on the Group 1 metal -Lithium + oxygen -- lithium oxide -Sodium + oxygen -- sodium oxide + sodium peroxide -Potassium + oxygen -- potassium peroxide + potassium superoxide What are halogens? - ANS Non-metals in Group 7 with coloured vapours What colour is fluorine? - ANS A very reactive, poisonous yellow gas What colour is chlorine? - ANS A fairly reactive, poisonous dense green gas What colour is bromine? - ANS A dense, poisonous red-brown volatile liquid What colour is iodine? - ANS A dark grey crystalline solid or a purple vapour What do halogens exist as? - ANS Molecules - pairs of atoms What do halogens form? - ANS 1) Molecular compounds - halogens share electrons via covalent bonding with other non-metals too achieves a full outer shell 2) Ionic compounds with metals - they form 1- ions called halides What do noble gases exist as? - ANS Monatomic gases - single atoms not bonded to each other What are the noble gases at room temperature? - ANS Colourless gases Are the noble gases flammable? - ANS No - they're non-flammable Why does the boiling point of noble gases increase as you move down the group? - ANS There's an increase in the number of electrons in each atom leading to greater intermolecular forces between them which to be overcome Paper Chromatography - Method - ANS 1) Draw a pencil line near the bottom of a sheet of filter paper 2) Add a spot of ink to the line & place the sheet in a beaker of solvent e.g. water - the solvent used depends on what's being tested - some compounds dissolve well in water, but sometimes other solvents e.g. ethanol are needed 3) Ensure the ink isn't touching the solvent - you don't want it to dissolve 4) Place a lid on top of the container to stop the solvent evaporating 5) The solvent seeps up the paper, carrying the ink with it 6) Each different dye in the ink will move up the paper at a different rate so that the dyes will separate out - each dye will form a spot in a different place, 1 spot per dye in the ink 7) If any of the dyes in the ink are insoluble in the solvent used, they'll stay on the baseline 8) When the solvent has nearly reached the top of the paper, take the paper out of the beaker & leave it to dry Simple Distillation - Method - ANS 1) The solution is heated. The part of the solution that has the lowest boiling point evaporates first 2) The vapour is then cooled, condensed & is collected 3) The rest of the solution is left behind in the flask What is the problem with simple distillation? - ANS You can only use it to separate things with very different boiling points - if the temperature goes higher than the boiling point of the substance with the highest boiling point, they will mix again Fractional Distillation - Method - ANS 1) Put your mixture in a flask & stick a fractionating column on top. Then you heat it 2) The different liquids will all have different boiling points - they'll evaporate at different temperatures 3) The liquid with the lowest boiling point evaporates first. When the temperature on the thermometer matches the boiling point of this liquid, it will reach the top of the column 4) Liquids with higher boiling points might also start to evaporate, but the column is cooler towards the top, therefore they will only get part of the way up before condensing & running back down towards the flask 5) When the first liquid has been collected, you raise the temperature until the next one reaches the top Radius of an atom - ANS 0.1 nanometers Radius of a nucleus - ANS 1/10,000 of the radius of an atom What type of ion do elements from Group 1 form? - ANS Positive ions What type of ion do elements from Group 7 form? - ANS Negative ions Describe how an ionic bond forms - ANS When a metal and a non-metal react together, the metal loses its one electron on its outer shell to form a positively charged ion. This one electron is gained by the non-metal to complete its outer shell, forming a negative ion. Describe the structure of a crystal of sodium chloride - ANS It's a giant ionic lattice. The positive sodium and negative chlorine ions form a closely packed regular arrangement and there are very strong electrostatic forces of attraction between the oppositely charged ions. List the main properties of ionic compounds - ANS 1) High melting and boiling points - many strong bonds between the ions 2) They can't conduct electricity when they're solid - the ions are held in a fixed arrangement therefore they can't pass on the electrical current. 3) They can conduct electricity when they're liquids because the ions are free to move therefore they can pass on the electrical current. 4) They dissolve easily in water - they are free to move in the solution and can carry electrical current. Describe how covalent bonds form - ANS When two non-metals bond together, they share electrons to make covalent bonds. The positively charged nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forces - this makes covalent bonds very strong. Explain why simple molecular compounds typically have low melting and boiling points - ANS The intermolecular forces between the atoms are very weak, therefore it takes only a small amount of energy to break them apart. Describe the structure of a polymer - ANS Polymers are long chains of repeating units joined together to make a long molecule. Between the atoms are strong covalent bonds. Give three examples of giant covalent substances - ANS -Diamond -Graphite -Silicon Dioxide Explain why graphite can conduct electricity - ANS It contains delocalised electrons which can carry electrical charge What is metallic bonding? - ANS The electrons in the outer shell of a metal atom are delocalised. There are strong forces of electrostatic attraction between the positive metal ions and the negative electrons. These forces of attraction hold the atoms together in a regular structure. List three properties of metals and explain how metallic structure causes each property - ANS 1)Solid at room temperature - they have very high melting and boiling points because a lot of energy is needed to break the strong electrostatic forces of attraction between the metal atoms and delocalised electrons. 2)Good conductors of heat and electricity - the delocalised electrons can carry electrical current and thermal energy through the structure. 3)Malleable - the layers of metal atoms can slide over each other Explain why alloys are harder than pure metals - ANS When two metals are mixed together, both of their atoms are different sizes which causes a disruption in the neat layers of metal atoms. This makes it more difficult for the layers to slide over each other. Name three states of matter - ANS Solid, liquid and gas State Symbols - ANS solid - s liquid - l gas - g aqueous - aq What is the name of the temperature at which a liquid becomes a gas? - ANS Boiling Describe giant covalent structures - ANS -All the atoms are bonded to each other by strong covalent bonds -They have very high melting and boiling points, therefore, lots of energy is required to break the covalent bonds -Most of them don't conduct electricity because they don't contain delocalised electrons or ions Describe the structure of diamond - ANS Each carbon atom forms four strong covalent bonds in a very rigid giant covalent structure. Describe the structure of graphite - ANS Each carbon atom forms three covalent bonds to create layers of hexagons. Each carbon atom also has one delocalised electron. What is silicon dioxide? - ANS Sand. Each grain of sand is one giant structure of silicon and oxygen. Describe the properties of diamond - ANS -Very hard because of its structure -Very high melting point because it takes a lot of energy to break the bonds -No delocalised electrons, therefore it cannot conduct electricity What is graphene? - ANS A sheet of carbon atoms joined together in hexagons - it's one atom thick, therefore it's a 2-dimensional compound The network of covalent bonds makes it very strong Very light - added to composite materials to improve their strength but not to add weight Contains delocalised electrons - conducts electricity through the whole structure Can be used in electronics What are fullerenes? - ANS Molecules of carbon, shaped like closed tubes or hollow balls - the carbon atoms are arranged in hexagons but also pentagons & heptagons Uses of Fullerenes - ANS 1) To 'cage' other molecules - the fullerene structure forms around another atom/molecule, which is then trapped inside - used to deliver drugs into the body 2) Make good industrial catalysts due to their large surface area 3) Make good lubricants Nanotubes - ANS Tiny carbon cylinders formed from fullerenes Ratio between length & diameter is very high Conduct electricity & thermal energy High tensile strength - don't break when stretched Used for nanotechnology - used in electronics or to strengthen materials without adding much weight e.g. tennis racket frames Melting - ANS When a solid is heated, the particles gain more energy which causes them to vibrate - weakens the forces that hold the solid together At the melting point, the particles will have enough energy to break free from their positions - the solid turns into a liquid Boiling - ANS When a liquid is heated, the particles will gain even more energy, making them move faster - weakens and breaks the bonds holding them together At the boiling point, the particles have enough energy to break their bonds - the liquid becomes a gas Condensing - ANS As a gas cools, the particles no longer have enough energy to overcome the force of attraction between them, causing bonds to form between the particles At the boiling point, so many bonds have formed between the gas particles that the gas becomes a liquid Freezing - ANS When a liquid cools, the particles have less energy, so move around less There's not enough energy to overcome the attraction between the particles, so more bonds form between them At the melting point, so many bonds have formed between the particles that they're held in place - the liquid becomes a solid What are coarse particles? - ANS Particles that have a diameter between 2,500 nm and 10,000 nm - also known as dust What are fine particles? - ANS Particles that have diameter between 100 nm and 2,500 nm What are nanoparticles? - ANS Particles that have a diameter between 1 nm and 100 nm - these are the smallest particles that contain only a few hundred atoms Equation for surface area to volume ratio - ANS Surface area to volume ratio = surface area / volume Do nanoparticles have a high or low surface area to volume ratio? - ANS Very high surface area to volume ratio - the surface area is very large compared to the volume, therefore, they make good catalysts What is nanoscience? - ANS The science that investigates the uses & properties of nanoparticles Uses for nanoparticles - ANS 1) Catalysts 2) Nanomedicine - they could deliver drugs right into the cells when they're needed as they're more easily absorbed by the body 3) Tiny electric circuits for computer chips - some conduct electricity 4) Silver nanoparticles have antibacterial properties - added to polymer fibres that are used to make surgical masks & wound dressings and they're added to deodorants 5) Used in cosmetics e.g. to improve moisturisers without making them really oily Effects of Nanoparticles on Health - ANS 1) The way they affect the body isn't fully understood 2) Some people are worried that products containing them have been made available before the effects on human health have been investigated properly 3) We don't know what the long-term impacts on health will be 4) Many people believe that products containing nanoparticles should be clearly labelled Benefits of Nanoparticles - ANS 1) Used in sun creams - shown to be better than the materials in traditional sun creams at protecting skin from harmful UV rays 2) Give better skin coverage than traditional sun creams Problems with Nanoparticles - ANS 1) Not yet clear whether the nanoparticles can get into your body, and if they do, whether they damage cells or not 2) Possible that when they are washed away, they might damage the environment Simple Molecular Structures - ANS Very strong covalent bonds Very weak intermolecular forces Most are liquids & gases at room temperature The bigger the molecule, the stronger the intermolecular forces Don't conduct electricity - no delocalised electrons or ions as they're not charged Why is Buckminsterfullerene a good lubricant? - ANS It's shaped like a hollow ball, thus it can roll What is the relative formula mass? - ANS The relative atomic masses of all the atoms in the molecular formula added together Formula for Percentage Mass - ANS Percentage Mass of an Element in a Compound = Relative Atomic Mass (Ar) x Number of atoms of that element / Relative Formula Mass (Mr) of the compound x 100 What is one mole? - ANS An amount of that a substance that contains an Avogadro number of particles What is the Avogadro constant? - ANS 6.02x10²³ What is the mass of one mole of atoms of a substance equal to? - ANS The relative formula mass of that substance Equation for Number of Moles - ANS Number of moles (mol) = Mass (g) of an element/compound / Mr of the element/compound Why is the mass conserved during a chemical reaction? - ANS No atoms are created and no atoms are destroyed Change of Mass - Increase - ANS If the mass increases, it's probably because one of the reactants is a gas that's found in the air (e.g. oxygen) and all the products are solids, liquids or aqueous Before the reaction, the gas is floating around in the air - it's there, but it's not contained in the reaction vessel, so you can't account for its mass When the gas reacts to form part of the product, it becomes contained inside the reaction vessel - so the total mass of the stuff inside the reaction vessel increases Change of Mass - Decrease - ANS If the mass decreases, it's probably because one of the products is a gas and all the reactants are solids, liquids or aqueous Before the reaction, all the reactants are contained in the reaction vessel If the vessel isn't enclosed, then the gas can escape from the reaction vessel as it's formed It's no longer contained in the reaction vessel, so you can't account for its mass - the total mass of the stuff inside the reaction vessel decreases Empirical Formula - ANS 1) Divide the mass of each substance by its relative formula mass to find the number of moles 2) Divide the number of moles of each substance by the smallest number of moles in the reaction 3) If any of the numbers aren't whole numbers, multiply all the numbers by the same amount so that they all become whole numbers 4) Write the balanced symbol equation for the reaction by putting these numbers in front of the chemical formula When is a reactant limiting? - ANS When it's completed used up in a reaction before the rest and causes the reaction to stop Why are reactants added in excess? - ANS To ensure that the limiting reactant is used up What is the amount of product directly proportional to? - ANS The amount of limiting reactant What happens when you add more reactant? - ANS There will be more reactant particles to take part in the reaction, therefore more product particles Mass of a Product - Calculation - ANS 1) Write out the balanced equation 2) Work out relative formula masses of the reactant and the product you want 3) Find out how many moles there are of the substance you know the mass of 4) Use the balanced equation to work out how many moles there'll be of the other substance - that's how many moles of product will be made of this many moles of reactant 5) Use the number of moles to calculate the mass What happens at the same temperature & pressure? - ANS Equal numbers of moles of any gas will occupy the same volume What happens at room temperature & pressure? - ANS One mole of any gas occupies 24dm³ Equation for Volume of Gas - ANS Volume of gas (dm³) = Mass of gas (g)/Mr of gas x 24 What is concentration? - ANS The amount of a substance in a certain volume of a solution The more solute there is in a given volume... - ANS ...The more concentrated the solution Equation for Concentration (g/dm³) - ANS Concentration (g/dm³) = Mass of solute (g) / Volume of solvent (dm³) Equation for Concentration (mol/dm³) - ANS Concentration (mol/dm³) = Number of moles of solute (mol) / Volume of solvent (dm³) What are titrations? - ANS Experiments that allow you to find the volumes needed for two solutions to react together completely How do you convert mol/dm³ to g/dm³? - ANS Find the concentration in mol/dm³ then convert the concentration using the equation: mass = moles x Mr What is atom economy? - ANS The atom economy (atom utilisation) of a reaction tells you how much of the mass of the reactants is wasted when manufacturing a chemical and how much ends up as useful products Equation for Atom Economy - ANS Atom economy = Relative formula mass of desired products / Relative formula mass of all reactants x 100 What does 100% atom economy mean? - ANS All the atoms in the reactants have been turned into useful (desired) products - the higher the atom economy, the 'greener' the process Why is a low atom economy bad? - ANS 1) The reactions use up resources very quickly 2) They make a lot of waste materials that have to be disposed of 3) The reactions are unsustainable - the raw materials will run out & the waste has to go somewhere 4) Reactions aren't usually profitable 5) Raw materials are expensive to buy 6) Waste products can be expensive to remove and dispose of responsibly How do you fix the problem of a low atom economy reaction? - ANS Find a use for the waste products - come up with a reaction that gives useful 'by-products' rather than useless ones How many products do the highest atom economy reactions have? - ANS Only one product - the lower the number of products, the higher the atomy economy is likely to be What is the yield? - ANS The amount of product you get - the more reactants there are, the higher the yield will be Equation for Percentage Yield - ANS Percentage Yield = mass of product actually made (g) / Maximum theoretical mass of product (g) x 100 Why do industrial processes need a high percentage yield? - ANS It reduces waste and costs In real life, do you ever get a 100% yield? - ANS No - some product or reactant always gets lost along the way Problems of getting a 100% yield - Problem 1 - ANS Not all reactants react to make a product - in reversible reactions, the products can turn back into reactants, so the yield will never be 100% Problems of getting a 100% yield - Problem 2 - ANS There might be side reactions - the reactants sometimes react differently to how you expect They might react with gases in the air, or impurities in the reaction mixture, which forms extra products other than the ones you want Problems of getting a 100% yield - Problem 3 - ANS When you filter a liquid to remove solid particles, you nearly always lose a bit of liquid or a bit of solid If you want to keep the liquid, you'll lose the bit that remains with the solid and filter paper If you want to keep the solid, some of it'll get left behind when you scrape it off the filter paper You'll always lose a bit of material when you transfer it from one container to another - some always gets left behind on the inside surface of the old container What neutralises an acid? - ANS A base (alkali) Neutralisation equation - ANS Acid + base -- salt + water What do acids form in water? - ANS Positive hydrogen ions What do alkalis form in water? - ANS Negative hydroxide ions Symbol equation of neutralisation - ANS H(positive) + OH(negative) -- H2O What do strong acids do in water? - ANS They ionise completely - all acid particles dissociate to release positive hydrogen ions What do weak acids do in solution? - ANS They don't fully ionise in solution - only a small proportion of acid particles dissociate to release positive hydrogen ions Examples of strong acids - ANS Sulfuric acid Hydrochloric acid Nitric acid Examples of weak acids - ANS Ethanoic acid Citric acid Carbonic acid How do acids react? - ANS The positive hydrogen ions react with other substances What happens if the concentration of positive hydrogen ions is higher? - ANS The rate of reaction will be faster, therefore strong acids will be more reactive than weak acids of the same concentration What is pH? - ANS A measure of the concentration of positive hydrogen ions in the solution For every decrease of 1 on the pH scale... - ANS ...The concentration of positive hydrogen ions increase by a factor of 10 - Logarithmic E.g. pH 4 has 10 times the concentration of pH 5 What does acid strength tell you? - ANS What proportion of the acid molecules ionise in water Are metal oxides and hydroxides bases or acids? - ANS Bases Are metal carbonates bases or acids? - ANS Bases Equation with a metal carbonate - ANS Acid + metal carbonate -- salt + water + carbon dioxide Reactivity series - ANS Potassium Sodium Lithium Calcium Magnesium Aluminium CARBON Zinc Iron Tin Lead HYDROGEN Copper Silver Gold Platinum Metals that react with water out of the RS - ANS Potassium, sodium, lithium and calcium Metals that don't react with water out of the RS - ANS Zinc, iron and copper Oxidation = - ANS Gain of oxygen Loss of electrons Reduction = - ANS Loss of oxygen Gain of electrons Metals higher than carbon... - ANS ...Have to be extracted by electrolysis Metals lower than carbon... - ANS ...Have to be extracted by carbon reduction What are redox reactions? - ANS REDuction and OXidation happen at the same time (REDOX) What is electrolysis? - ANS The process by which ionic substances are broken down into simple substances using electricity What happens during electrolysis? - ANS An electric current is passed through an electrolyte which causes the ions to move towards the electrodes where they react and the compound decomposes Cathode - ANS Negative electrode Positive ions move towards it Electrons are gained Reduction happens Anode - ANS Positive electrode Negative ions move towards it Electrons are lost Oxidation happens Can an ionic solid be electrolysed? - ANS No, because the ions are in fixed positions and can't move Can a molten ionic compound be electrolysed? - ANS Yes, because the ions can move freely and conduct electricity Aluminium Oxide - Cathode Half Equation - ANS Al(three plus) + 3e(minus) -- Al Aluminium Oxide - Anode Half Equation - ANS 2O(two minus) -- O2 + 4e(minus) Cathode - If the element is more reactive than hydrogen... - ANS ...Hydrogen gas will be produced Anode - If there are no halogen ions (halide ions)... - ANS ...Oxygen will be produced Cathode - If the element is less reactive than hydrogen... - ANS ...The element will be released from the cathode Anode - If there are halogen ions (halide ions)... - ANS ...They will be released from the anode Hydrogen Half Equation - ANS 2H(plus) + 2e(minus) -- H2 Chlorine Half Equation - ANS 2Cl(minus) -- Cl2 + 2e(minus) What is an ore? - ANS A rock which contains a metal that's worth extracting - there's enough of the metal in it to make it economic to extract What are the most common ores? - ANS Oxides and sulfides What is a negative ion? - ANS Anion What is a positive ion? - ANS Cation Method on making salt crystals - Evaporation - ANS 1) Put goggles on and tie hair back. Pour sulfuric acid into a beaker 2) Using a bunsen burner, heatproof mat, tripod and gauze, heat the acid until it just starts to boil 3) Off the heat, stir some copper oxide into the acid using a stirring rod. 4) Continue to add a little bit more after each addition has dissolved until there is excess copper oxide at the bottom of the beaker and the acid has turned blue 5) Put filter paper into a filter then put that into a conical flask - filter the solution into the conical flask 6) Once filtered, pour the solution into a petri dish and leave alone overnight until salt crystals have formed Safety Precautions on Crystals Experiment - ANS 1) If during the experiment you spill acid on your hands, wash it off immediately 2) If you break a glass beaker, ensure everyone knows where the glass is and carefully sweep it up with a dustpan and brush 3) Ensure all long hair is tied up to prevent spilling acid on it What are titrations used for? - ANS Finding out exactly how much acid is needed to neutralise a quantity of alkali - or vice versa Titration Method - ANS 1) Rinse out the burette & pipette using distilled water - ensure every last drop is thoroughly out 2) Write the acid on one beaker and the alkali on the other. Pour the acid & alkali into their beakers 3) Fix the metal rod into the clamp stand and attach the clamp holder. Slip the burette firmly inside the holder and place the stand on a surface where the top of the burette is at eye level or below. Place a ceramic square under the burette and a plastic pot on that. Put a funnel in the burette 4) Pour 50cm³ of the acid into the burette & overshoot by 1-2cm³. Let the excess acid run out into the pot. Remove the funnel & use the laminated piece of paper to ensure the volume of acid is exactly 50cm³ 5) Use the pipette filler to fill the pipette with 50cm³ of alkali. Add it to the conical flask with some indicator. The alkali should turn pink 6) Carefully, add the acid to the alkali, swirling the conical flask to mix the solutions. As soon as the hydroxide turns colourless, stop adding the acid. Use the laminated piece of paper to identify the volume of acid added 7) Record your results and repeat the experiment 4 more times, or until you find 2-3 results that are within 0.2cm³ of each other. Calculate an average 8) Repeat the experiment with the average but omit the indicator Litmus indicator - ANS Acid = red Alkali = blue Methyl orange - ANS Acid = red Alkali = yellow Phenolphthalein - ANS Acid = colourless Alkali = pink Reaction of Metal with Water - ANS Metal + Water -- Metal Hydroxide + Hydrogen Formation of a metal ore = - ANS Oxidation Extraction of a metal = - ANS Reduction Making Soluble Salts Using an Insoluble Base - Method - ANS 1) Gently warm the dilute acid using a Bunsen burner, then turn off the Bunsen burner 2) Add the insoluble base to the acid a bit at a time, until no more reacts. You'll know when all the acid has been neutralised because even after stirring, the excess solid will just sink to the bottom of the flask 3) Filter out the excess solid to get the salt solution 4) To get pure, solid crystals of the salt, gently heat the solution using a water bath or an electric heater to evaporate some of the water, then stop heating it & leave the solution to cool. Crystals of salt should form which can be filtered out of the solution & then dried What's the difference between a burette and a pipette? - ANS 1) A burette measures varying volumes 2) A pipette measures fixed volumes Exothermic reactions - ANS Heat energy is given out to the surroundings during a chemical reaction. The temperature increases Endothermic reactions - ANS Heat is taken in from the surroundings during a chemical reaction. The temperature decreases Examples of exothermic reactions - ANS Combustion Neutralisation Many oxidation reactions Examples of endothermic reactions - ANS Thermal decomposition What is the activation energy? - ANS The energy needed to start the reaction It is the minimum amount of energy the reactants need to collide with each other and react What do most exothermic reactions involve? - ANS Burning fuels Reaction profiles - exothermic - ANS Products are at a lower energy than the reactants Reaction profiles - endothermic - ANS Products are at a higher energy than the reactants What is bond breaking? - ANS Endothermic process - energy is supplied to break existing bonds What is bonding formation? - ANS Exothermic process - energy is released when new bonds are formed What is an electrochemical cell? - ANS A basic system made up of 2 different electrodes (usually metals, in order to conduct electricity) in contact with an electrolyte What is an electrolyte? - ANS A liquid that contains ions which react with electrodes What happens in an electrochemical cell? - ANS The chemical reactions between the electrodes & the electrolyte set up a charge difference between the electrodes If the electrodes are connected by a wire, the charge is able to flow & electricity is produced A voltmeter can be connected to the circuit to measure the voltage of the cell What causes the charge difference (voltage) in an electrochemical cell? - ANS Different metals react differently with the same electrolyte What affects the voltage of a cell? - ANS 1) The type of electrodes used 2) Concentration of the electrolyte 3) Temperature How is a battery formed? - ANS By connecting two or more cells together in series - the voltages are combined so there is a bigger voltage overall for the battery Why are some chemical reactions irreversible at the electrodes? - ANS Over time, the reacting particles get used up and turned into products of the reaction - once any of the reactants are used up, the reaction can't happen, therefore no electricity is produced If the products can't be turned back into reactants, the cell won't be recharged What are non-rechargeable batteries? - ANS Batteries which contain cells which use irreversible reactions - once one of the reactants is used up, they don't produce any more charge, therefore you have to replace them E.g. alkaline batteries How can you reverse a reaction in a rechargeable cell? - ANS Connecting the cell to an external electric current What is a fuel cell? - ANS An electrical cell that's been supplied with a fuel and oxygen (or air) and uses energy from the reaction between them to produce electrical energy efficiently When the fuel enters the cell, it becomes oxidised and sets up a p.d. within the cell Hydrogen-Oxygen Fuel Cell - ANS Combines hydrogen & oxygen to produce nice, clean water and release energy What type of reaction do hydrogen-oxygen fuel cells involve? - ANS A redox reaction Process of electrolysis in a hydrogen-oxygen fuel cell - ANS 1) Hydrogen goes into the anode compartment and oxygen goes into the cathode compartment 2) At the anode, hydrogen loses electrons to produce H⁺ ions - oxidation 3) At the cathode, oxygen gains electrons from the cathode and reacts with the H⁺ ions to make water - reduction 4) The electrons flow through an external circuit from the anode to the cathode - electric current 5) The overall reaction is hydrogen + oxygen -- water What is the electrolyte for a hydrogen-oxygen fuel cell? - ANS A solution of potassium hydroxide What are the electrodes for a hydrogen-oxygen fuel cell? - ANS Porous carbon with a catalyst Why will the electrolyte affect the size of the voltage in a cell? - ANS The different ions in solution will react differently with the metal electrodes used Why are conventional fuels bad? - ANS For vehicles (e.g. petrol), they have a finite supply and they're very polluting Why are hydrogen-oxygen fuel cells better than batteries for cars? - ANS 1) Don't produce as many pollutants as other fuels as the only by-products are water & heat - batteries for electric vehicles are polluting to dispose of due to the highly toxic metal compounds they contain 2) Batteries have a limit to the number of times they can be recharged and they're more expensive to make 3) Store less energy than fuel cells - would need to be recharged more often, and recharging takes a long time Testing the effect of acid concentration on the energy released during neutralisation - Method - ANS 1) Put 25cm³ of 0.25mol/dm³ of HCl & NaOH in separate beakers 2) Place the beakers in a water bath set to 25°C until they are both at the same temperature 3) Add the HCl followed by the NaOH to a polystyrene cup with a lid 4) Take the temperature of the mixture every 30 seconds & record the highest temperature 5) Repeat steps 1-4 using 0.5mol/dm³ & then 1mol/dm³ of HCl Measuring Energy Transfer - Method - ANS 1) Fill a polystyrene cup with the reaction mixture & measure the temperature. Record it in a table 2) Put a lid on the cup then put it in a large beaker. Measure the temperature of the mixture every 30 seconds for 5 minutes 3) Repeat this experiment but with different insulating materials inside the large beaker, wrapped around the cup e.g. cotton wool, newspaper etc 4) Compare the different temperatures for each material to find the best insulator