Physical Chemistry (CHEMISTRY)

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What is the strongest pH for an acid?
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pH 0
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What is the strongest pH for an alkali?
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pH 14
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What is a neutral pH and give an example of a substance at this pH
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pH 7 – Water
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What is the colour spectrum for universal indicator?
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What is the colour spectrum for litmus paper?
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Red – acidic Purple – neutral Blue – alkaline
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What is the colour spectrum for phenolphthalein?
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Colourless for neutral and acidic solutions Bright pink for alkaline solutions
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What is the colour spectrum for methyl orange?
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Red in acidic solutions Yellow in alkaline solutions
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What is an acid?
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A solution that contains H⁺ ions and has a pH of less than 7
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What is a base?
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A substance that can neutralise acids
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What is an alkali?
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A soluble base that contains OH⁻ ions and has a pH greater than 7
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What is the formula for a neutralisation reaction?
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Acid + Base → Salt + Water
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Give an example of a neutralisation reaction
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H⁺(aq) + OH⁻ (aq) → H₂O (l)
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What is the formula for an acid and metal oxide reaction?
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Acid + Metal Oxide → Salt + Water
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What do metal oxides tend to be?
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Bases
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If the acid is hydrochloric acid, the salt will be a metal…
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Chloride
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If the acid is sulphuric acid, the salt will be a metal…
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Sulfate
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If the acid is nitric acid, the salt will be a metal…
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Nitrate
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What is the formula for a reaction between an acid and a metal carbonate?
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Acid + Metal Carbonate → Salt + Water + Carbonate
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WHAT ARE THE SOLUBILITY RULES
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∙Sodium, potassium ammonium and nitrate salts are always soluble ∙Most chlorides are soluble – except for silver chloride ∙Most sulphates are soluble – except for barium sulphate and calcium sulphate ∙Most carbonates are insoluble – except for sodium, potassium and ammonium
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What processes would I use to get a soluble salt from an insoluble base?
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Neutralisation (Filtration and Evaporate)
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What tend to be insoluble bases?
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Metal oxides, metal carbonates or metal hydroxides
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How would I make Copper Nitrate?
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Add copper carbonate to some nitric acid. Once you see excess copper carbonate sinking to the bottom and staying there, the neutralisation is complete. Filter out the excess base to get the salt solution. Place this in an evaporating basin and evaporate until the solution has halved in volume. Leave the basin in a warm place to evaporate excess water and retrieve the salt crystals.
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Why can you not do a filtration exercise for making soluble salts with an alkali?
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Because alkalis are soluble bases, you can’t filter them out.
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What practical would you use to create a soluble salt from an alkali and how?
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Use a titration. Place some phenolphthalein to the acid and slowly pour in the alkali from a burette until you’ve just neutralised the acid and the pink can no longer disappear. Note down how much acid you’ve used and repeat without the indicator so the salt isn’t contaminated.
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How would one make an insoluble salt?
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Simply mix together two solutions that contain the ions you need and filter the solution to retrieve the salts.
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What are the two formulas I could use to find the number of moles for one of these practicals?
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Moles = Concentration x Volume Moles = Mass —– Mr
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What are the four things that control the rate of a reaction?
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Temperature Catalyst Concentration Size of particles/Surface area
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Label a rate of reaction graph
Label a rate of reaction graph
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What is the formula for the rate of reaction?
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Rate = amount of reactant used/product formed ———————————— time
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Explain the process of a precipitation reaction and how the rate can be measured
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Some products of a reaction form a precipitate which may cloud the solution. Observe the marker through the solution and measure how long it takes to disappear – the faster the marker disappears, the faster the rate
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What is wrong with the precipitation method?
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Subject to human error – different people might not agree over the exact point a cross disappears
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Explain the process in which a gas is given off and make a comment on the practical’s accuracy and give an example of this reaction
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As the gas is released in a practical, keep the flask on a measuring balance to determine how fast the reaction is working. When the mass balance stops decreasing, the practical will have stopped. As the mass balance is very accurate and will make a complete stop, there is very little error to be made. An example would be placing a magnesium strip into hydrochloric acid and seeing how much mass is lost.
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Explain how one would find the rate of reaction from the volume of gas given off in a reaction and make a comment on its accuracy and give an example of this reaction
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By using a practical which gives off gas, connect the conical flask to a delivery tube feeding into a gas syringe and time how long it takes for the marker on the gas syringe to stop moving. As gas syringes tend to give results to the nearest millimetre, it is very accurate, however, some gas might be lost when attempting to put the bung in place or there might be too much gas, blowing the plunger out completely. An example would be placing marble chips in hydrochloric acid and measuring its CO₂ production.
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Explain reaction rates by using collision theory
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The rate of reaction depends on how often and how hard the reacting particles collide with each other.
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Why would a higher temperature increase the rate of reaction?
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With an increase in temperature, the particles have more energy and move faster. By moving faster, they’re colliding more frequently.
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Why would a higher concentration or pressure increase the rate of reaction?
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A higher concentration means that there are more particles of reactant moving, thus making it more likely for reactant particles to collide. In a higher pressure, the particles are more squashed so they are going to collide more frequently.
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Why would a larger surface area increase the rate of reaction?
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The particles in the solution will have more area to work on and collide with, so useful collisions will happen more often.
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Why would a catalyst increase the rate of reaction?
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They increase the number of successful collisions by lowering the activation energy of the reaction.
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What is the only factor that increases the speed of collisions?
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Increasing temperature
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Is energy supplied or released when breaking existing bonds? What type of process is this?
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It is supplied – endothermic process
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Is energy supplied or released when new bonds are formed? What type of process is this?
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It is released – exothermic process
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Explain what is meant by the term ‘exothermic reaction’
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A reaction that gives out energy to the surroundings, usually in the form of heat and usually shown by a rise in temperature. The energy released in bond formation is greater than the energy used in breaking previous bonds.
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Explain what is meant by the term ‘endothermic reaction’
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A reaction that takes in energy from the surroundings, usually in the for of heat and shown by a fall in temperature. The energy required to break bonds. The energy required to break old bonds is greater than the energy released when new ones are formed.
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What is ‘enthalpy change’?
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The overall change in energy in a reaction (ΔH)
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What is the unit for ΔH?
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kJ/mole
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Is the enthalpy change positive or negative in an endothermic reaction?
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Positive
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Is the enthalpy change positive or negative in an exothermic reaction?
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Negative
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What does an exothermic reaction graph look like?
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∙The products are at a lower energy than the reactants ∙Difference in height represents the energy given out
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What does an endothermic reaction graph look like?
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∙Products at a higher energy than products ∙Difference in height represents the energy taken in during the experiment
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What do catalysts do to the activation energy in a reaction?
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They lower the activation needed by providing an alternative reaction pathway making the reaction faster as more collisions have the required activation energy.
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What MUST you remember about catalysts in reactions?
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They are never completely used up
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What is the formula for ΔH?
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Enthalpy Change (ΔH) = Total energy absorbed to break bonds – Total energy released in making bonds
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Bendy Mexicans
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B – breaking bonds = END – endothermic M – making bonds = EX – exothermic
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What is the use of calorimetry?
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It allows you to measure the amount of energy transferred in a chemical reaction
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What is the formula for ‘energy produced’ in calorimetry?
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4.2 x water capacity x temperature change
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What is the formula for molar enthalpy change?
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Energy released (kJ) —————— Moles of fuel used
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If a reversible reaction takes place in a closed system…
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It will reach a state of equilibrium
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What is meant by the term ‘dynamic equilibrium’?
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Reactions are still taking place in both directions but the overall effect is nil because the forward and reverse reactions cancel each other out (they are taking place at exactly the same rate in both directions)
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What is meant by the term ‘reversible reaction’?
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The products of the reaction can themselves react to produce the original reactants
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What happens if you raise the temperature of a reversible reaction?
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The endothermic reaction will increase to use up the extra heat
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What happens in you decrease the temperature of a reversible reaction?
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The exothermic reaction will increase to give out more heat
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What happens if you raise the pressure in a reversible reaction?
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It will favour the side which produces fewer molecules of gas
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What happens if you lower the pressure in a reversible reaction?
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It will favour the side which produces more molecules of gas

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