Chemistry Topic 4

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What is the pH scale?
0= strongly acidic, 7= neutral, 14= strongly alkaline.
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How are indicators useful?
They change colour depending on their pH. Universal indicator is a combination of dyes, litmus paper tells you if a solution is acidic or alkaline, phenolphthalein changes from colourless in acidic to bright pink in alkaline.
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What is the equation for the neutralisation of bases in acids?
acid + base -> salt + water. Can be seen in terms of H+ and OH- ions: H+ + OH- -> H2O
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What do acids react with metal oxides to make?
acid + metal oxide -> salt + water
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What do metal carbonates make with acids?
acid + metal carbonate -> salt + water + carbon dioxide
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What salts are soluble?
(dissolve in water) Sodium, potassium, ammonium, nitrates, most chlorides (except silver chloride), most sulfates (except barium sulfate & calcium sulfate). Most carbonates are insoluble, except sodium,potassium and ammonium carbonates.
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Making soluble salts using acids and insoluble bases.
Most metal oxides/carbonates/hydroxides are insoluble. Add metal oxide/carbonate/hydroxide to acid- sold dissolves&reacts, filter excess base to get salt solution.
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Making soluble salts using an alkali.
Add exactly right amount of alkali to neutralise acid- use indicator and titration, repeat using same volumes of alkali and acid without indicator so salt isn't contaminated.
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Precipitation reactions by making insoluble salts.
If the salt you want to make is insoluble, use this. Two solutions containing needed ions, mix.
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What do titration's allow you to do?
Find out exactly how much acid is needed to neutralise a quantity of alkali (or vice versa).
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How do you do a titration?
Pipette&pipette filler, 25cm^3 alkali to a conical flask- 2/3 drops indcator. Fill burette with acid at eye level. Use burette, add acid to alkali slowly, swirl conical flask. Indicator changes colour when alkali neutralised.Volume recorded&repeat.
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Number of moles.
number of moles = concentration x volume
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Different rates of reactions- what do you expect?
Slowest- rusting of iron. Moderate speed - metal with acid (gentle stream of bubbles produced). Really fast- explosion.
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What affects the rate of reaction?
Temperature, concentration (or pressure for gases), catalyst and size of particles (or surface area).
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Rate of reaction equation.
amount of reactant used or amount of product formed / time
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How do precipitates allow you to measure the speed of a reaction?
Observe a marker through the solution and measure how long it takes for it to disappear, the quicker it goes the faster the reaction. Only works for reactions where the initial solution is colourless. Subjective, people may not agree.
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How does the change in mass help to measure the speed of a reaction?
As the gas is released, mass disappearing easily measured on a balance. Quicker reading drops, faster the reaction. Mass stops changing= reaction over. Graphs easy to plot. Most accurate, but releases gas straight into room.
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How does the volume of gas given off help to measure the speed of a reaction?
Gas syringe to measure. More gas given off in a time interval= faster. Gas stops being produced = finished. Plotted easily, accurate to nearest mm, can be vigorous.
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Reaction of hydrochloric acid and marble chips.
Surface area. Measure volume of gas in syringe, readings at regular intervals. Table of readings, plot as graph. Repeat, exactly same V of acid & mass of marble chips but crushed up. Repeat, same mass of powdered marble instead of marble chips.
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Reaction of magnesium metal with dilute hydrochloric acid.
Effect of increased concentration. Gives off H2 gas, measure with a mass balance. Readings at regular intervals, table and graph. Repeat more concentrated but same amount Mg and V of HCl.
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Sodium thiosulfate and hydrochloric acid.
Clear solutions to start. Form yellow precipitate of sulfur. Black mark disappears through cloudy sulfur, time. Repeated at different temps, water bath. Table, graph. Repeat, can change concentration. Effects of temperature.
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Decomposition of hydrogen peroxide.
2H2O2->2H2O+O2. Manganese(IV)oxide catalyst. O2 gas given off, gas syringe, table and graph. Effect of a catalyst.
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Exothermic reactions.
DeltaH is -ve. Products are at a lower energy than the reactants. Graph: initial rise in line representing the energy needed to break the old bonds (activation energy), then decreases.
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Endothermic reactions.
DeltaH is +ve. Goes up with activation energy, different in heigh represents the energy taken in during the reaction.
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The effect of catalysts on activation energy.
Activation energy=the minimum energy needed by reacting particles for the reaction to occur. A catalyst makes the reaction happen faster by proving an alternative reaction pathway with lower activation energy. Graph:lower curve, same overall change.
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What is bond energy?
The amount of energy in a bond. It can vary slightly depending what compound the bond is in. Use these to calculate the enthalpy change for a reaction. Add up energy of bonds broken and subtract by energy of bonds made.
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Equation for working out enthalpy change.
Total energy absorbed to break bonds - total energy released in making bonds.
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What does calorimetry do?
Allows you to measure the amount of energy transferred in a chemical reaction.
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Calorimetry- dissolving, displacement and neutralisation reactions.
Take temperature of reagents (making sure they're the same), mix them and measure temp of solution at end of reaction. Use polystyrene cup. A lot of energy lost to surroundings.Reduce this by putting cup in beaker of cotton wool-more insulation- lid.
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Calorimetry- combustion.
Burn fuel+use flame to heat water. Metal container, usually copper as it conducts heat well. Reduce draughts-screen. 50g water in copper can+take temp, weigh spirit burner+lid.Heat H2O+stir, put out flame using burner lid, final temp H2O,weigh all.
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How do you calculate the heat energy transferred with combustion?
Measure how much fuel burned and temperature change of water, work out how much energy supplied by each g of fuel. Waters specific heat capactity- amount of energy needed to raise the temp of 1g of H2O by 1degree. (4.2J/g/degreesC)
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How do you calculate the molar enthalpy change?
Calculate amount of energy transferred, holw many moles of fuel produced this heat, moles in substance, then find heat produced by 1 mole.
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What is a reversible reaction?
The products of the reaction can react to produce the original reactants.
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Thermal decomposition of ammonium chloride.
Nh4CL(s) NH3(g)+HCl(g). Ammonium chloride is a white solid, heated and makes ammonia&HCl gasses, cools and re-forms ammonium chloride.
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What is a dynamic equilibrium?
The reactions are taking place in both directions but there is no overall effect as the forward and backward reactions cancel each other out. They take place at exactly the same rate in both directions.
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How does changing the temperature effect the equilibrium?
All reactions are exothermic in one way and endothermic in the other. Raise temp=endothermic increases to use up extra heat. Reduce temp=exothermic reaction increases to give out more heat.
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How does changing the pressure effect the equilibrium?
Most gaseous reactions have more molecules or moles of gas on one side than the other. Raise pressure=encourage reaction producing fewer molecules of gas. Lower pressure= encourage reaction producing more molecules of gas.
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Other cards in this set

Card 2


How are indicators useful?


They change colour depending on their pH. Universal indicator is a combination of dyes, litmus paper tells you if a solution is acidic or alkaline, phenolphthalein changes from colourless in acidic to bright pink in alkaline.

Card 3


What is the equation for the neutralisation of bases in acids?


Preview of the front of card 3

Card 4


What do acids react with metal oxides to make?


Preview of the front of card 4

Card 5


What do metal carbonates make with acids?


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