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Chemistry Paper 1 > Chemical Changes > Flashcards

Chemical Changes Flashcards

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1
Q

State the Equation for Metal Reactions with Oxygen

A

Metal + Oxygen → Metal Oxide

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2
Q

Describe what is Meant by Oxidation and Reduction

A

-If an element gains, oxygen during a reaction, it is oxidised. If an element loses (no longer in a compound with) oxygen during a reaction, it is reduced.

-Therefore, when a metal reacts with oxygen, the metal is oxidised and the oxygen is reduced.

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3
Q

Describe what Is Meant by the Reactivity Series

A

-The reactivity series is a list of metals in order of their reactivity towards other substances.

-The reactivity of metals is determined by how easily they lose electrons to form positive ions. The higher up the series, the more easily the metal forms a positive ion.

-When metals react with water or acid, they lose electrons and from positive ions. So, the higher up the series, the more easily the metal reacts with water or acid.

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4
Q

Describe how Different Elements React with Water and Dilute Acid

A

-Calcium reacts quite rapidly with water at room temperature.

-Magnesium does not react with water at room temperature but it reacts rapidly with dilute acid.

  • Zinc does not react with water at room temperature but it does react quite rapidly with dilute acid.

-Iron does not react with water at room temperature but it does react slowly with dilute acid.

  • Copper does not react with either water at room temperature or with dilute acid.
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5
Q

Explain why Magnesium Reacts Rapidly with Acid, Zinc Quite Rapidly and Iron Slowly

A

-Magnesium is the most reactive of the three metals (it is higher in the reactivity series), so magnesium reacts the most rapidly with dilute acid.

-Zinc is higher in the reactivity series than iron, so zinc reacts faster than iron.

-Iron is the least reactive so reacts slowest.

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6
Q

Explain why Copper Does not React with Dilute Acids

A

Copper is below hydrogen in the reactivity series. This means that copper is less reactive than hydrogen, so copper cannot displace hydrogen from acids.

-This means that copper will not react with
dilute acid.

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7
Q

Give the Equation for Metal Reactions with Acid

A

Metal + Acid → Salt + Hydrogen

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8
Q

Give the Equation for Metal Reactions with Water

A

Metal + Water → Metal Hydroxide + Hydrogen

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9
Q

Describe what is Meant by an Ore

A

-An ore is a rock containing a enough of a metal compound to be economically viable to extract.

-Some elements are too reactive to exist on their own in the ground. Instead, they exist combined with other elements (typically oxygen or sulfur) as compounds called ores.

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10
Q

Describe what is meant by a Displacement Reaction

A

-A more reactive element will push out (displace) a less reactive element from its compound.

-In a displacement reaction, it is always the metal ion that gains electrons and is reduced. The metal atom always loses electrons and is oxidised.

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11
Q

Explain why Carbon can Displace Iron

A

The reactivity series shows us that carbon is more reactive than iron. This means that carbon can displace iron from its compounds.

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12
Q

Give the Equation for Metal Oxide Reactions with Carbon

A

Metal Oxide + Carbon → Metal + Carbon Oxide

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13
Q

Explain why Hydrogen Cannot be Used to Extract Iron

A

-Hydrogen could not be used to displace iron because hydrogen is less reactive than iron (it is lower in the reactivity series).

-This means that hydrogen cannot displace iron from its compounds.

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14
Q

Explain why Gold Existing as Nuggets in the Earth’s Crust Shows that it is Unreactive

A

-A very small number of metals (eg gold) can be found as nuggets in the Earth’s crust.

-Because they have not reacted with other elements (eg oxygen), this tells us that these metals are highly unreactive.

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15
Q

Describe what is Involved in an Ionic Equation

A

-In an ionic equation, only the particles that react and the products they form are shown.

-Any ions that are the same in the reactants and the products are not featured. These are called spectator ions.

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16
Q

Describe what OIL RIG Stands For

A

-Oxidation is Loss (of electrons)

-Reduction is Gain (of electrons)

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17
Q

Describe the Placement of Electrons in a Half Equation

A

-If the electron(s) is on the side of the products, then it is has been lost. This means the metal in the reaction is oxidised.

-If the electron(s) is on the side of the reactants, then it has been gained. This means the metal in the reaction is reduced.

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18
Q

Describe what is Meant by an Acid, Alkali and Base

A

-An acid is a substance that forms aqueous solution with a pH of less than 7. Acids form H+ ions in water.

-A base neutralises an acid to form water. They have a pH greater than 7. Examples include: calcium carbonate, magnesium oxide and copper hydroxide.

-An alkali is a base that dissolves in water to form hydroxide ions. Examples include: sodium hydroxide, potassium oxide, sodium carbonate and ammonium hydroxide.

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19
Q

State the Names, Symbols and Salts Formed by Different Acids

A

-Hydrochloric acid (HCL aq) forms Chloride (CL -) ions.

-Sulfuric acid (H2SO4 aq) forms Sulfate (SO4 2-) ions.

-Nitric acid (HNO3 aq) forms Nitrate (NO3 -) ions.

-Phosphoric acid (H3PO4 aq) forms Phosphate (PO4 3-) ions.

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20
Q

Describe what is Meant by Neutralisation

A

Neutralisation is a reaction between acids and bases.

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21
Q

Give the Equation a Neutralisation Reaction

A

Acid + Base → Salt + Water

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22
Q

Give the Equation for Reaction Between an Acid and an Alkali

A

Acid + Alkali → Water

H+ + OH- → H2O

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23
Q

Describe what is Meant by an Indicator

A

An indicator is a dye that changes colour depending on the pH.

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24
Q

State Common Indicators and Their Colour Changes

A

-Methyl Orange: (red in acid, yellow in alkali)

-Phenolphalein: (colourless in acid, pink in alkali)

-Universal Indicator (red/orange/yellow in acid, blue/purple in alkali, green if neutral)

-In universal indicator, acids have a value of 1-6, alkalis have a value of 8-14 and a neutral substance has a value of 7.

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25
Q

Explain how a pH Probe can be Used to Determine the pH of a Solution

A

-A pH probe attached to a pH meter can be used to measure the pH electronically.

-The probe is placed in the solution being measured and the pH is given on a digital display as a numerical value, meaning it is more accurate then an indicator.

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26
Q

Give the Equation for Metal Carbonate Reactions with Acids

A

Metal Carbonate + Acid → Salt + Water + Carbon Dioxide

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27
Q

Give the Equation for Metal Oxide and Hydroxide Reactions with Acids

A

Metal Oxide + Acid → Salt + Water

Metal Hydroxide + Acid → Salt + Water

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28
Q

Describe a Method for the Making Soluble Salts Required Practical

A

-Pour 40cm^3 of acid to a beaker. Heat the acid over a Bunsen burner until it is almost boiling. The reaction is faster when the acid is hot.

-Now, add a spatula of copper oxide and stir. Continue adding copper oxide until no more can react.

-Remove the excess copper oxide by filtration. Pour the solution through filter paper in a filter funnel and into a new beaker.

-Place the filtered solution into an evaporating basin. Put this over boiling water on top of a Bunsen burner. Heat until crystals start to appear and there is some solution left.

-Leave to cool so that more crystals form. Finally, remove and dry the crystals using paper towels..

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29
Q

Explain why Copper metal Cannot be Used to Produce Copper Sulfate Using Sulfuric Acid in the Making Soluble Salts Required Practical

A

-Copper metal cannot be used to produce copper sulfate using dilute sulfuric acid.

-This is because copper is lower than hydrogen on the reactivity series (copper is less reactive than hydrogen).

-This means that copper cannot displace hydrogen from acids.

30
Q

State the Salts Produced from Different Acids in the Making Soluble Salts Required Practical

A

-Copper chloride is produced using hydrochloric acid.

-Copper sulfate is produced using sulfuric acid.

-Copper nitrate is produced using nitric acid.

31
Q

Explain why it is Important that There is No Acid Left at the End of the Making Soluble Salts Required Practical

A

-At the end of the reaction, the products should only be salt and water and should be neutral (as this is a neutralisation reaction).

-However, if there is acid left at the end of the reaction, then the salt and water will be contaminated with the acid and the solution will not be neutral.

32
Q

Explain why it is Important that the Acid is Not Boiling in the Making Soluble Salts Required Practical

A

-Boiling acid is dangerous. When we add our copper oxide, a reaction will take place and if we use boiling acid, then the reaction could be extremely rapid.

-This could cause boiling acid to spill over the side of the beaker. We do need to use warm acid though in order to make the reaction fast enough.

33
Q

Explain why the Solution Turns Blue in the Making Soluble Salts Required Practical

A

-The solution turns blue because we have made the salt copper sulfate. Copper sulfate is a blue compound.

34
Q

Explain how we Know When the Reaction has Stopped in the Making Soluble Salts Required Practical

A

-We know that the reaction has stopped because there will be unreacted copper oxide remaining in the beaker.

-Copper oxide is a black powder and when the reaction has stopped, we can see the copper oxide sitting on the bottom of the beaker.

-The reaction stops at this stage because all of the acid has reacted (it is the limiting reactant).

35
Q

Describe what is Meant by a Strong Acid

A

-Strong acids ionise completely in water. All acid particles dissociate to release H+ ions.

-Examples include: hydrochloric acid, sulfuric acid and nitric acid.

36
Q

Describe what is Meant by a Weak Acid

A

-Weak acids do not fully ionise in solution. Only a small proportion of acid particles dissociate to release H+ ions.

-The ionisation of a weak acid is a reversible reaction which sets up an equilibrium between the undissociated and dissociated acid.

-Since only a few of the acid particles release H+ ions, the position of equilibrium lies far to the left.

-Examples include: ethanoic acid, citric acid and carbolic acid.

37
Q

Describe how the Concentration of H+ Ions in an Acid Affects Its Rate of Reaction

A

-Reactions of acids involve the H+ ions reacting with other substances.

-If the concentration of H+ ions is higher, the rate of reaction is faster.

-This means that strong acids will be more reactive than weak acids of the same concentration.

38
Q

Explain what Information the pH Scale Gives About Acids

A

-The pH scale gives information about the concentration of hydrogen ions H+ produced by an acid.

-As the pH scale decreases by one unit, the concentration of hydrogen ions H+ increases by 10 times.

-Strong acids have a lower pH than weak acids for a given concentration.

39
Q

Explain why Strong Acids have a Lower pH than Weak Acids

A

-Strong acids fully ionise in aqueous solution whereas weak acids only partially ionise.

-This means for a given concentration of acid, strong acids produce a higher concentration of H+ than weak acids.

-The pH scale gives us an idea of the concentration of H+, with a lower pH meaning a higher H+ concentration. So strong acids have a lower pH than weak acids.

40
Q

Explain what happens the pH of an Acid if Water is Added

A

-If we add more water to an acid, the pH will increase. When we add more water, we dilute the acid, (the concentration of H+ ions decreases).

-A higher pH value means a lower concentration of H+ ions.

41
Q

Describe the Difference Between the Strength and Concentration of an Acid

A

-Acid strength tells you what proportion of the acid molecules ionise in water.

-The concentration of an acid measures how much acid there is in a certain volume of water.

-The larger the amount of acid there is in a certain volume, the more concentrated the acid is.

42
Q

Describe what is Meant by Concentration

A

Concentration is the measure of the number of particles in a given volume.

43
Q

Give the Calculation for Concentration

A

Concentration (mol/^3) = Moles (mol) / Volume (dm^3

44
Q

Describe how to Convert dm^3 to cm^3

A

-To convert cm^3 to dm^3, divide by 1000.

-To convert dm^3 to cm^3, multiply by 100

45
Q

Describe a Method for the Titration Required Practical

A

-Use a pipette to transfer 25cm^3 of the alkali (of a known concentration) into a conical flask. Now, add five drops of an indicator such as methyl orange. Place the conical flask onto a white tile.

-Fill a burette to 0.0cm^3 with acid (of an unknown concentration), making sure the top is closed. Measure and record the volume of the acid in the burette.

-Gradually add the acid to the alkali so that it trickles from the burette. Swirl the flask until there is a permanent colour change and close the burette so no more acid can leave..

-Measure and record the new volume of the acid.

-Repeat the titration until two readings within 0.1cm^3 are recorded. Take a mean of the concordant readings. Use these readings to carry out the titration calculation.

46
Q

Explain why a Conical Flask is Better to Use than a Beaker in the Titration Required Practical

A

-If you carry out a titration in a beaker, there is a risk that some of the acid or alkali could splash out. This would affect the results of the titration.

-However, if we use a conical flask, there is a much lower chance of splashing.

47
Q

Explain why a Pipette and Burette is Used to Measure the Volume of Alkali and Acid in the Titration Required Practical

A

A pipette and burette is used when we want to measure a single volume of liquid accurately.

48
Q

Explain why Methyl Orange is Used Instead of Universal Indicator in the Titration Required Practical

A

-When we carry out a titration, we need to find the exact point where the solution is neutral (the end point).

-This is very difficult to do with universal indicator as it has a whole range of colours.

-Indicators such as methyl orange have a much smaller range of colour changes so it is much easier to see the
neutral point

49
Q

Explain why a White Tile is Used in the Titration Required Practical

A

-Placing a white tile under the conical flask makes it easier to see the indicator change colour when the solution is neutral.

-This gives more valid results.

50
Q

Explain why it is Important to Swirl the Solution While Adding Acid in the Titration Required Practical

A

Swirling mixes the acid with the alkali. This ensures that the acid and alkali react fully and that the indicator changes colour to show this.

51
Q

State the Colour Change of Methyl Orange when Neutralisation Takes Place

A

Methyl orange is yellow in alkaline solutions and orange when neutral.

52
Q

Describe what is Meant by Electrolysis, Electrode and Electrolyte

A

-Electrolysis is using electricity to split an ionic compound (electrolyte) inti elements.

-An electrolyte is a molten/dissolved ionic compound. It can conduct electricity.

-An electrode is a metal or graphite rod that connects the electrolyte to the wires.

53
Q

Explain why Graphite or a Metal are Used as Electrodes

A

-Electrodes must be able to conduct electricity.

-Both graphite and metals make good electrodes. This is because they have delocalised electrons which means that they conduct electricity.

54
Q

Explain why Electrolysis Cannot be Done on Solid Salts

A

Electrolysis cannot be done on solid salts. This is because the ions in a salt are in fixed positions so cannot move and carry charge through the lattice.

55
Q

Explain why the Cathode is Negative and the Anode is Positive

A

-The cathode is connected to the negative terminal of a power pack. This means that the cathode is covered with electrons and has a negative charge.

-The anode is connected to the positive terminal which means that it has a lack of electrons (as they are taken in by the power pack). This is why the anode has a positive charge.

56
Q

Describe what Happens During Electrolysis

A

-During electrolysis, an electric current is passed through an electrolyte. The ions move towards the electrodes where they react and the compound decomposes.

-The positive ions in the electrolyte will move towards the cathode (negative electrode) and gain electrons (they are reduced).

-The negative ions in the electrolyte will move towards the anode (positive electrode) and lose electrons (they are oxidised).

-This creates a flow of charge through the electrolyte as ions travel to the electrodes. As ions gain or lose electrons, they form the uncharged element and are discharged from the electrolyte.

57
Q

Describe the Electrolysis of Magnesium Oxide

A

-The magnesium ion is attracted to and discharged at the negative electrode. Here, it gains two electrons and discharges an ion. Pure magnesium is formed.

-The oxide ion is attracted to and discharge at the positive electrode. Here, it loses two electrons and discharges an ion. Pure oxygen is formed.

58
Q

Explain why Positive Ions are Attracted to the Cathode and Negative Ions to the Anode

A

-The positive ions are attracted to the cathode because the cathode is negative and the ions are positive. Opposite charges are attracted to each other.

-In the case of the negative ions, the anode is positive and the ions are negative. Again, opposite charges are attracted.

59
Q

Explain Whether the Reactions at the Anode and Cathode are Reduction or Oxidation

A

-The reaction at the cathode is an example of a reduction. This is because the positive ions gain electrons.

-The reaction at the anode is an example of an oxidation. This is because the negative ions lose electrons .

60
Q

Explain why Carbon Cannot be Used to Extract Materials High Up in the Reactivity Series

A

Because they are higher in the reactivity series than carbon, this means that carbon cannot be used to extract these metals as it cannot displace them from their compounds.

61
Q

Describe the Electrolysis of Aluminium Oxide

A

-Aluminium is extracted from the ore bauxite (which contains aluminium oxide) by electrolysis.

-Aluminium has a very high melting point so it is mixed with cryolite to lower the melting point.

-The molten mixture contains free ion so will conduct electricity.

-The positive Al3+ ions are attracted to the negative electrode where they gain three electrons and become pure aluminium. These then sink to the bottom of the electrolysis tank.

-The negative O2- ions are attracted to the positive electrode where they each lose two electrons and become pure oxygen. The pure oxygen then combine to form O2 molecules.

62
Q

Explain why Aluminium is Useful for Making Aircraft Bodies

A

Aluminium is a very low density metal. This is important for aircraft bodies which must be light.

63
Q

Describe the Purpose of Cryolite

A

-Aluminium oxide has an extremely high melting point (around 2000oC). This is due to the very strong electrostatic forces of attraction between the ions.

-Cryolite lowers the melting point. This reduces
the amount of energy needed for melting and saves money.

64
Q

Describe the Properties of Graphite Which make it Useful as Electrodes

A

-Graphite is an excellent conductor of electricity (as it has delocalised electrons).

-Graphite also has a very high melting point which means that it can be used for electrolysis at very high temperatures without melting.

65
Q

Explain why Molten Aluminium is a Good Conductor of Electricity

A

Molten aluminium oxide is a good conductor of electricity because the electrostatic forces of attraction between the ions have been broken. This means that the ions can move and carry a charge.

66
Q

Explain why Aluminium Ions are Attracted to the Cathode and Oxide Ions to the Anode

A

-The cathode is negatively charged. This means that the positively charged Al3+ ions are attracted to the cathode (as opposite charges are attracted to each other).

-The anode is positively charged. This means that the negatively charged O2- ions are attracted to the anode (again as opposite charges attract).

67
Q

Explain why the Anode Must be Replaced Regularly when Doing Electrolysis on Aluminium Oxide

A

-Electrolysis of aluminium oxide takes place at very high temperatures.

-The oxygen produced at the anode reacts with the graphite (which is the element carbon) to make carbon dioxide. This is why the anode must be replaced regularly.

68
Q

Describe why it is Expensive to Extract Metals Using Electrolysis of Molten Compounds

A

-Firstly, it takes a great deal of energy to maintain the very high temperatures needed to keep the compound molten.

-Secondly, a great deal of energy is required to produce the electrical current.

69
Q

Explain why Electrolysis of Aqueous Solutions will also Include H+ and OH- Ions

A

In aqueous solutions, as well as the ions from the ionic compound, there will be hydrogen ions (H+) and hydroxide ions (OH-) from the water.

70
Q

Describe what is Formed at the Negative Electrode During Electrolysis of Aqueous Solutions

A

-At the cathode, if H+ ions and metal ions are present, hydrogen gas will be produced if the metal ions form a pure metal that is more reactive than hydrogen.

-If the metal ions form a pure metal that is less reactive than hydrogen, a solid layer of the pure metal will be produced instead.

71
Q

Describe what is Formed at the Positive Electrode During Electrolysis of Aqueous Solutions

A

-At the anode, if OH- ions and halide ions are present, halogens will be formed.

-If no halide ions are present, then the OH- ions are discharged and oxygen will be formed.

-Any sulfate, nitrate or carbonate ions remain in the solution. Only the hydroxide ions are discharged.

72
Q

Explain why Platinum is Often Used as an Electrode During Electrolysis

A

-Platinum is a very unreactive metal. This means that it will not react with any of the products of electrolysis. Scientists say that platinum is an inert ( unreactive ) electrode.

Chemistry Paper 1 (5 decks)

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