Chemistry 2b Flashcards
What is one of the slowest reactions?
The rusting of iron
What is an example of a moderate speed reaction?
A metal (like magnesium) reacting with acid to produce a gentle stream of bubbles
What is a really fast reaction?
An explosion where it is all over in a fraction of a second
What are the four things that the rate of a reaction depends on?
Temperature, concentration (or pressure for gasses), catalyst and surface area of solids (or size of solid pieces)
What would a graph for a slow reaction look like?
The line wouldn’t be very steep
What happens to graphs as the rate of reaction quickens?
The slope of the graphs gets steeper. The steepest and longest line would mean that there were more reactants as well
What can cause an increased rate if reaction?
Increase in temperature, Increase in concentration/pressure, if a catalyst is added or by a solid reactant being crushed up into smaller bits
What are the two different things you can measure to work out the rate of reaction?
How quickly the reactants are used up or how quickly the products are formed
What is the calculation to work out the rate of reaction?
Rate of reaction = Amount of reactant used or amount of product formed DIVIDED BY the time
How can precipitation be used to measure the rate of a reaction?
This is when the product is a precipitate and clouds the solution, you watch a mark through the solution (X on paper under the glass) and measure how long it takes to disappear. The quicker it disappears, the quicker the rate of reaction. Only works when the initial substance is see-through.
What is the issue with working out the rate of reaction by timing the precipitation?
The result is subjective-Different people would have different thoughts as to when the mark has disappeared
How can a change in mass (usually gas given off) be used as a way to measure the rate of reaction?
This is used when the reaction produces a gas. Use a mass balance. Weighs less as the gas leaves. The quicker the reading on the balance drops, the quicker the rate of reaction. Then a rate of reaction graph is used to plot the results from this method
Why is measuring the change in mass a very accurate way of testing the rate of reaction?
Because a mass balance is very accurate and you can easily see how much it has changed. Fact not oppinion
What is the disadvantage of measuring the change in mass for rate of reaction?
The gas is released straight into the room which can be dangerous, depending on the substance
How can the volume of gas being given off be used as a way to measure weight of reaction?
Use a gas syringe to measure the volume of gas given off. The more gas given off in a certain time interval, the faster the reaction. A graph of gas volume against time elapsed can be plotted to show the rate of reaction.
What are the good and bad points of measuring rate of reaction by the volume of gas given off?
Gas syringes give volumes accurate to the nearest millimetre usually so they are quite accurate however if the reaction is too vigorous, you can break the syringe
What is the reaction of hydrochloric acid and marble chips often used for?
To demonstrate the effect of breaking a solid into smaller bits
How do you complete the experiment of hydrochloric acid and marble chips?
Measure the volume of gas evolved with a gas syringe and take readings at regular intervals then make a table of readings and plot them as a graph. Repeat the experiment with the same volume of acid and exactly the same mass of marble chips but crunched up more and then repeat again but with the same mass of powdered chalk instead of marble chips
Why does the size of marble chip affect the rate of reaction?
Finer particles means the marble has a larger surface area which causes more frequent collisions so the rate of reaction is faster
What is the reaction of magnesium metal with dilute hydrochloric acid usually used to measure?
The effects of increased concentration ( same as the marble/acid reaction)
How do we use the magnesium metal/dilute HCl reaction to measure rate of reaction?
The reaction gives off hydrogen gas which can be measured with a mass balance and then repeat with more concentrated acid solutions but the same amount of magnesium and the same volume of acid. It can then be plotted as a graph to make the results easier to analyse
In a graph for the magnesium/HCl experiment, what would a steeper graph mean?
A higher concentration - a faster rate of reaction
What is the experiment for sodium thiosulfate and HCl?
The chemicals are both clear solutions, together they react to form a yellow precipitate (sulfur). Time how long it takes for a black mark under the glass to disappear. Can be repeated at different temperatures but can be hard to do accurately and safely. Best way is to use a water bath first. Keep depth of liquid the same. This reaction can also test the effects of concentration. Don’t get a graph, just results
What do the results for this experiment show?
The higher the temperature, the quicker the reaction and therefore the less time it takes for the mark to disappear
What is the decomposition of hydrogen peroxide usually used to measure?
It is usually used to show the effect of different catalysts. It can also be used to measure the effect of temperature or of concentration of the H2O2 solution
What is the equation for the decomposition of hydrogen peroxide?
2H2O2(aq) -> 22H2O(l) + O2(g)
The decomposition is often quite slow, how can it be sped up?
By adding a sprinkle of manganese(IV) oxide catalyst
Other catalysts which work are found in where?
Potato peel, and blood
How can the decomposition of hydrogen peroxide be measured?
Oxygen gas is given off which provides an ideal way to measure the rate of reaction using the gas syringe method.
What would the results of this method show?
Better catalysts give a quicker reaction which is shown by a steeper graph that levels off quickly
What do more collisions mean?
More collisions increases the rate of reaction
What are collisions?
How often the reacting particles collide successfully
How does a higher temperature increase collisions?
A higher temperature means the particles move around quicker, meaning they’re going collide more often
How does a higher concentration (or pressure) increase collisions?
A higher concentration means that there are more particles that can knock into each other and a higher pressure means that there are more particles squashed closer together so they will collide more often
How does a larger surface area increase collision?
Because the particles have more area to work on so there will be more collisions
What else does a higher temperature cause in collision theory?
Increasing the temperature causes faster collisions
What needs to happen for a reaction to take place?
The particles need to collide with enough energy, the minimum amount of energy needed is known as the activation energy. A higher temperature means that there will be more particles colliding with enough energy to make the reaction happen.
What is a catalyst?
A catalyst is a substance which speeds up a reaction, without being changed or used up in the reaction
How does a solid catalyst work?
By giving the reacting particles a surface to stick to. This increases the number of successful collisions and so speeds up the reaction
What do catalysts help to reduce?
Costs in industrial reactions
How do catalysts save money?
Because it means the plant doesn’t need to operate for as long to produce the same amount of stuff
How are catalysts good for sustainable development?
They mean that the reactions can take place at lower temperature. This reduces the energy used up in the reaction (energy cost)
What are the disadvantages of catalysts?
They are expensive to buy and often need to removed and cleaned, different use different catalysts so if you make more than one product you probably need more than one catalyst. Also they can be poisoned by impurities and stop working so you have to keep your reaction mixture clean
What is another advantage of catalysts?
They never run out so usually when you buy one, you don’t have to buy another one
What is an exothermic reaction?
A reaction that gives out heat
What is the full definition of an exothermic reaction?
An exothermic reaction is one which transfers energy to the surroundings, usually in the form of heat and usually shown by a rise in temperature
What is the best example of an exothermic reaction?
Burning fuels, also known as combustion, it gives out a lot of heat
What are other examples of exothermic reactions?
Neutralisation (acid+alkali) reactions. Also many oxidation reaction, eg sodium + water makes heat.
What are some everyday uses of exothermic reactions?
Hand warmers use the oxidation of iron in air to generate heat. Self heating cans of hot chocolate and coffee also rely on exothermic reactions between chemicals in their bases
What happens in an endothermic reaction?
Heat is taken out
What is the full definition of an endothermic reaction?
AN endothermic reaction is one which takes in energy from the surroundings, usually in the form of heat and is usually shown by a fall in temperature
Are endothermic reactions more or less common than exothermic reactions?
They are much less common
What is a good example of an ednothermic reaction?
Thermal decompositions. E.G CaCO3->CaO+CO2 Heat must be applied to make calcium carbonate decompose to make quicklime
What is an everyday use of an endothermic reaction?
Some sports injury packs use endothermic reactions-they take in heat and the pack becomes very cold, they are mire convenient than carrying ice around
What sort of reactions can reversible reactions be?
They can be endothermic and exothermic
What happens with a reversible reaction is it is endothermic in one direction?
It will be exothermic in the other direction. The energy absorbed by the endothermic reaction is equal to the energy released by the exothermic reaction
What is a good example of a reversible reaction?
The thermal decomposition of hydrated copper sulfate.
Hydrated copper sulgfat anhydrous copper sulfate + water
How do you complete the thermal composition of hydrated copper sulfate?
You heat the blue hydrated copper sulfate crystals and the water is driven off, leaving white anhydrous copper sulfate powder (endothermic). If you add a couple of drops of water to the white powder, the blue crystals come back again (exothermic)
What does anhydrous mean?
Without water like hydrated means with water
What does the pH scale go from and to?
From 0 to 14
What is the pH scale?
A measure of how acidic or alkaline a solution is
What pH would the strongest acid have?
pH 0
What pH would the strongest alkali have?
pH 14
What pH is neutral?
pH 7 eg pure waters
What is an indicator?
A dye that changes colour depending on whether it is above or below a certain pH.
What is universal indicator?
A combination of dyes, it is very useful for estimating the pH of a solution
What do acids and bases do to each other?
The neutralise each other
What is the equation for neutralisation?
Acid + Base -> salt + water
What is the equation for neutralisation in terms of H+ (acids form H+ ions in water) and OH- (alkalis form OH- ions in water) ions?
H+ (aq) + OH- (aq) -> H2O (I) in
What pH are the products formed when an acid neutralises a base (Or the other way around)?
They are neutral (pH7)
What are the state symbols?
(s)-solid (l)-liquid (g)-gas (aq)-dissolved in water
What happens when you react metals with salts?
Salt is formed
Whats the equation for making salts?
Acid + metal -> salt + hydrogen
What makes this reaction faster?
The reactiveness of the metal e.g. sodium, a very reactive metal, reacts explosively
Why does copper not react with dilute acids at all?
Because it’s less reactive than hydrogen
How is the speed of this reaction indicated?
By the rate at which the bubbles are given off, the hydrogen is confirmed by the burning split test which makes a squeaky pop if there is hydrogen
What does the name of the salt produced depend on?
Which metal is used and which acid is used
What sort of salt does hydrochloric acid produce?
Chloride salts eg magnesium chloride, aluminium chloride and zinc chloride
What sort of salt does sulphuric acid produce?
Sulfate salts eg magnesium sulfate, aluminium sulfate and zinc sulfate
What sort of salt does nitric acid produce?
Nitrate salts when neutralised however thats when it reacts with alkalis , with metals it produces nitrogen oxides instead
What are metal oxides and metal hydroxides an example of?
Bases
Do all metal oxides and metal hydroxides react with acids to form salt and water?
Yes, some dissolve in water but even bases that don’t dissolve in water still react with acids
What is the equation for making salts with metal oxide?
Acid + metal oxide -> salt + water
What is the equation for making salts with metal hydroxide?
Acid+metal hydroxide->Salt+water
What type of reactions were they?
Neutralisation reactions
What is an example of an equation for making salt?
Hydrochloric acid + copper oxide -> copper chloride +water
What is a symbol equation for making salts?
H2SO4(aq) + ZnO(s) -> ZnSO4(aq) + H20(l)
Ammonia can be neutralised with nitric acid to make what?
Fertiliser
What is the word equation for this?
Ammonia + nitric acid -> ammonium nitrate
What is the symbol equation for this?
NH3(aq) + HNO3(aq) -> NH4NO3(aq)
Why is this reaction different to most neutralisation reaction?
Because no water is produced, just the ammonium salt
Why is ammonium nitrate an especially good fertiliser?
Because it has nitrogen from two sources, the ammonia and the nitric acid and plants need nitrogen to make proteins
Why is it important to know if a salt is soluble or not when your making it?
So you know what method to use
What salts are mostly soluble in water?
Chlorides, sulfates and nitrates except lead chloride, lead sulphate and silver chloride)
What salts are mostly insoluble in water?
Oxides and hydroxides
How do you make soluble salts using a metal or an insoluble base?
Pick the right acid and metal/insoluble base. Add the metal, metal oxide or hydroxide to the acid, the sold will dissolve in the acids as it reacts then filter out the excess metal, metal oxide or metal hydroxide to get the salt solution
How do you get pure solid crystals from the salt?
Evaporate some of the water to make the solution more concentrated and then leave the rest to evaporate very slowly, this is called crystallisation
How do you know when all the acid has been neutralised?
Because the excess solid will just sink to the bottom of the flask
How do you make soluble salts using an alkali?
You have to add exactly the right amount of alkali to just neutralise the acid, you need to use an indicator to show when the reaction’s finished then repeat using exactly the same volumes of alkali and acid so the salt isn’t contaminated with indicator. Then evaporate off the water to crystallise the salt as normal
Why cant you use the method for metal or insoluble bases to make salts using an alkali?
Because you cant tell whether the reaction is finished, you cant add an excess to the acid and filter out whats left
What is it called when you make insoluble salts?
Precipitation reactions
How do you make insoluble salts?
Pick two solutions that contain the ions you need. Once the salt has precipitated out all you have to do is filter it from the solution, wash it and dry it on filter paper
What else can precipitation reactions be used to do?
Remove poisonous ions e.g. lead from drinking water. Calcium and magnesium ions can also be removed from water this way as they make water hard which stops soap lathering properly
What is an example of making insoluble salts?
To make lead chloride you need a solution that has lead ions and one that has chloride ions so you can mix the lead nitrate solution with sodium chloride solution
What is the symbol equation for this?
PB(NO3)2(aq) + 2NaCl(aq)->PBCl2(s) + 2NaNO3(aq)
What is an example of making soluble salts?
If you want to make copper chloride mix hydrochloric acid and copper oxide
What is the symbol equation for this?
CuO(s) + 2HCl(aq) -> CuCl2(aq) + H2O(l)
What does electrolysis mean?
Splitting up with electricity
What happens if you pass an electric current through an ionic substances that molten or in solution?
It breaks down into the elements it made of (electrolysis)
What does electrolysis?
A liquid to conduct the electricity called the electrolyte
What do electrolytes contain?
Free ions-they’re usually the molten or dissolved ionic substance . Its the free ions which conduct the electricity and allow the whole thing to work
What has to happen for an electrical circuit to be complete?
There has to be a flow of electrons. Electrons are taken away from ions at the positive electrode(anode) and given to other ions at the negative electrode(cathode) As ions gain or lose electrons they become atoms or molecules and are released
Electrolysis ALWAYS involves oxidation and reduction, what are they?
Oxidation is a gain of electrons/loss of electrons while reduction is a gain of electrons
What does the acronym OIL RIG stand for?
Oxidation is loss Reduction is gain
Where are positive ions attracted to?
The negative electrode where they gain elections (reductions) Lead is produced here during electrolysis of molten lead bromide
Where are negative ions attracted?
The positive electrode where they lose electrons (oxidation) Bromine is produced here during electrolysis of molten lead bromide
(Electrolysis of lead bromide) what happens at the negative electrode?
One lead ion accepts two electrons to become one lead atom
(Electrolysis of lead bromide) what happens at the positive electrode?
Two bromide ions lose one electron each and become one bromine molecule
What affects the products formed by electrolysis?
Reactivity
What can happen if there more than two free ions in the electrolyte?
E.G. If a salt is dissolved in water there will also be some H+ and OH- ions
What happens at the negative electrode if metal ions and H+ ions are present?
The metal ions will stay in solution if the metal is more reactive than hydrogen. This is because the more reactive an element, the keener it is to stay as ions so hydrogens will be produced unless the metal is lees reactive than it
What happens at the positive electrode if OH- and halide ions are present?
Then molecules of chlorine, bromine or iodine will be formed. If no halide is present, then oxygen will be formed
What products are formed in the electrolysis of sodium chloride?
Hydrogen, chlorine and sodium hydroxide
Where are H+ ions released from?
Water
What happens at the negative electrode during the electrolysis of sodium chloride solution?
Two hydrogen ions accept two electrons to become one hydrogen molecule
What happens at the positive electrode during the electrolysis of sodium chloride solution?
Two chloride ions lose their electrons and become one chlorine molecule
What happens to the sodium ions during the electrolysis of sodium chloride solution?
The sodium ions stay in solution because they’re more reactive than hydrogen. Hydroxide ions from water are also left this means that sodium hydroxide is left in the solution
What are half equations for?
They show the reactions at the electrodes. The main thing is to make sure the number of electrons is the same for both half-equations. The atoms have to be balanced
What are the half-equations for the electrolysis of sodium chloride?
Negative electrode: 2H+ + 2e- -> H2
Positive electrode: 2Cl- -> Cl2 +2e-
What are the half-equations for the electrolysis of molten lead bromide?
Negative electrode: Pb2+ + 2e- -> Pb
Positive electrode: 2Br- -> Br2 + 2e-
What are the useful products from the electrolysis of sodium chloride solution?
Chlorine has many uses e.g. in the production of bleach and plastics. Sodium hydroxide is a very strong alkali and is used widely in the chemical industry e.g. to make soap
How is aluminium removed from its ore?
Electrolysis
What is aluminium’s main ore?
Bauxite and after mining and purifying a white powder is left which is pure aluminium oxide, Al2O3
Why is melting pure aluminium oxide hard?
It has a very high melting of over 2000 degrees celsius
What is something you can do instead of melting it?
Dissolving it in molten cryolite (a less common ore of aluminium) because this brings the temperature down to about 900 degrees celsius
What are the electrodes made of?
Carbon (graphite) a good conductor of electricity.
What happens at the positive/negative electrode?
Aluminium from at the negative electrode and oxygen from at the positive electrode
What are the half equations for this?
Negative electrode: Al3+ + 3e- -> Al
Positive electrode: 2O2- -> O2 +4e-
Why do the positive electrodes gradually get eaten away and have to be replaced every now and again?
The oxygen reacts with the carbon in the electrode to produce carbon dioxide
What is electroplating?
It uses electrolysis to coat the surface of one metal with another metal, e.g. you might want to electroplate silver onto a brass cup to make it look nice
What is the negative and positive electrode for?
The negative electrode is the metal object you want to plate and the positive electrode is the pure metal you want it to be plated with
What is the electrolyte for?
To contain ions of the plating metal (the ions that plate the metal object come from the solution, while the positive electrode keeps the solution ‘topped up’)
What is an example of this?
To electroplate silver onto a brass cup you’d make the brass cup the negative electrode to attract the positive sliver ions, a lump of pure silver the positive electrode and dip them into a solution of silver ions e.g. silver nitrate
There are different types of electroplating, what is decoration?
Silver is attractive but very expensive, its much cheaper to plate a boring brass cup with silver than it is to make the cup out of solid silver but it looks just as pretty
What is conduction?
Metals like copper conduct electricity well, because of this they’re often used to plate metals for electronic circuits and computers
