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GCSE Chemistry > C5 - Chemical Changes > Flashcards

C5 - Chemical Changes Flashcards

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1
Q

What is the Reactivity Series?

A

A list of metals in order of their reactivity, with the most reactive metals at the top, and the least reactive metals at the bottom.

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2
Q

How have the metals been placed in order of reactivity?

A

Based on their reactions with water and dilute acid.

E.g copper does not react with water at all, and therefore can be used to make water pipes.

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3
Q

What are the 3 basic metal reactions?

A

1) Metal + Oxygen ———> Metal Oxide
2) Metal + Acid ———> Salt + Hydrogen
3) Metal + Water ———> Metal Hydroxide + Hydrogen

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4
Q

What gas is given off when a metal reacts with acid or water?

A

Hydrogen

Do’ squeaky pop test’ to determine whether hydrogen is present.

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5
Q

How do Potassium, Sodium and Lithium react with water and acid?

What conclusion can we make about these 3 Group 1 elements?

A

Water: Fizz, give off a hydrogen gas and leave a metal hydroxide alkaline solution

Acid: Explodes

Conclusion: They are at the top of the reactivity series.

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6
Q

How do Calcium and Magnesium react with water and acid?

What conclusion can we make about these 2 group 2 elements?

A

Water: Calcium fizzes. Magnesium has a very slow reaction.

Acid: Both fizz, forming a salt and giving off hydrogen gas.

Conclusion: These 2 group 2 elements are the next metals on the reactivity series.

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7
Q

How does Aluminium react with water and acid?

What conclusion can you make about this Group 3 element?

A

Water: Very slow reaction.

Acid: Fizz, forms salt and gives off hydrogen gas.

Conclusion: Aluminium is after group 2’s calcium and magnesium in the reactivity series.

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8
Q

How do Zinc and Iron react with water and acid?

What conclusion can you make about these 2 transition metals?

A

Water: Very slow reaction.

Acid: Fizz, forms a salt and hydrogen gas is given off.

Conclusion: Zinc releases 2+ ions and Iron released 3+ ions. Therefore, they are below the actual group 2 and 3 elements, but at the top of the transition elements.

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9
Q

How do Tin and Lead react with water and acid?

A

Water: Slight reaction with steam.

Acid: Reacts very slowly with warm acid.

Conclusion: These 2 Group 4 elements slot in behind the transition elements zinc and iron.

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10
Q

How do Copper, Silver, Gold and Platinum react with water and acid?

A

Water: No reaction, even with steam.

Acid: No reaction.

Conclusion: These particular transition elements will be at the bottom of the reactivity series. They will be useful for jewellery and piping.

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11
Q

Based on the results of these reactions, list the metals in order of reactivity:

*Exclude Lithium

A 
Potassium -G1
Sodium - G1
Calcium - G2
Magnesium - G2
Aluminium - G3
Zinc - TM
Iron - TM
Tin - G4
Lead - G4
Copper - TM
Silver - TM
Gold - TM
Platinum - TM

Peggy Sue Cooks Meat At Zoos in Tropical London Causing Severe Gut Pain (13 words)

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12
Q

What is the rule about displacement in relation to metals?

A

A more reactive metal will displace a less reactive metal from its aqueous solution.

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13
Q

Is there a displacement for the following?:

a) Iron + Zinc Sulfate
b) Zinc + Copper Sulfate

A

a) No, Zinc is higher up than Iron
b) Yes, Zinc is higher up than Copper

Zinc + Copper Sulfate ———> Zinc Sulfate + Copper

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14
Q

What is an Ionic Equation and what is a good method for it?

A

An ionic equation shows only the atoms and ions change in an equation.

Whatever stays the same, you cancel out.

  • When writing ionic equations, first split all aqueous solutions into their ions as this is what would happen in a reaction. E.g HCl (aq), split it into H+ and Cl-.
  • After this you just write out what remains.

Example:

HCl (aq) + NaOH(aq) ———> NaCl(aq) + H2O(l)

Split (aq) into ions:

H+ and Cl-
Na+ and OH-

Na+ and Cl-
Leave water.

Then CANCEL the unchanged ions, and you are left with:

H+ (aq) + OH-(aq) ———> H2O(l)

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15
Q

Write the correct ionic symbol equation for:

Mg(s) + CuSO4(aq) ———>MgSO4(aq) + Cu(s)

A

Mg(s) + Cu2+(aq) ———> Mg2+(aq) + Cu(s)

In this equation the (SO4)2- ions remain the same, so do not appear in this equation.

The reason the copper and magnesium become ions, is because aqueous solutions break up into their free ions. In this case copper and magnesium both break up as 2+.

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16
Q

What is a Half Equation?

A

A half equation is used to show the transfer of electrons (e-) in a reaction.

This transfer of electrons happens when atoms become ions, and when ions become atoms again.

In these reactions, electrons can be lost or gained.

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17
Q

In terms of electrons, what is the loss of electrons known as?

A

Oxidation

OILRIG

Oxidation is loss

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18
Q

In terms of electrons, what is the gain of electrons known as?

A

Reduction

OILRIG

Reduction is gain

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19
Q

Just by looking at half-equations, how can we tell when electrons are being lost or gained?

A

-If the electrons are after the arrow, they are being lost, so oxidation is happening.

E.g Na ——>Na+ + e-

-If the electrons are before the arrow, they are being gained, so reduction is happening.

E.g Na+ + e- ——>Na

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20
Q

Write the half equation for Cu ——>Cu2+ :

Straight Away you can tell this is gonna be an oxidation as the charge increases from left to right, meaning there is a loss of electrons.

A

Is the equation balanced: Yes

Cu charge = 0
Cu2+ charge = +2

We need to make the side without the lowest charge (right hand side) equal to the lowest charge (in this case 0). The only way to do this is by adding 2 electrons (2-) which cancel out the 2+ of copper.

So the half-equation is:

Cu ——> Cu2+ + 2e-

This is Oxidation as the electrons are after the arrow and they are being lost.

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21
Q

Write the half equation for O[2-] ——> O2 :

Straight Away you can tell this is gonna be an oxidation as the charge increases from left to right, meaning there is a loss of electrons.

A

Is the equation balanced: No

Write 2O2- ——> O2

2O2- charge = -4 (2 x -2)
O2 chareg = 0

We need to make the side without the lowest charge (right hand side) equal to the lowest charge (-4). So we do this by adding 4 electrons (4-) to the right hand side. The charge on the left is -4. And the charge on the right is now -4.

So the half equation is:

2O2- ——> O2 + 4e-

This is Oxidation as the electrons are after the arrow and electrons are being lost.

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22
Q

What is the half equation for Cl2 ——> Cl- :

Straight Away you can tell this is gonna be a reduction as the charge decreases from left to right, meaning there is a gain of electrons.

A

Is the equation balanced: No

Write Cl2 ——> 2Cl-

Cl2 charge = 0
2Cl- charge = -2 (2 x - 1)

We need to make the side without the lowest charge (left hand side) equal to the lowest charge. So we do this by adding 2 electrons to the left hand side, making the charge (2-).

So the half equation is:

Cl2 + 2e- ——> 2Cl-

This is an example of reduction as the electrons are before the arrow, and are being gained.

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23
Q

What is the half equation for Na+ ——> Na:

Straight Away you can tell this is gonna be a reduction as the charge decreases from left to right, meaning there is a gain of electrons.

A

Is the equation balanced: Yes

Na+ charge = 1
Na charge = 0

Need to make the side without the lowest charge (left hand side) equalmto the lowest charge. So we do this by adding 1 electron to the left hand side, making the charge -1.

So the half equation is:

Na+ + e- ——> Na

This is an example of reduction as the electrons are before the arrow, and are being gained.

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24
Q

Why are displacement reactions known as redox reactions?

A

Because of the fact that they are examples of reduction and oxidation taking place.

Red (uction) - ox (idation)

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25
Q

Why are carbon and hydrogen given positions in the reactivity series?

A

Because of displacement reactions. Hydrogen cannot displace zinc, iron, tin or lead, but carbon can. However, copper, silver, gold and platinum can be extracted using carbon or hydrogen.

Carbon slots in between Aluminium and Zinc (At Zoos)

Hydrogen slots in between Lead and Copper (London Causing)

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26
Q

What is a metal ore?

A

A metal ore is a rock that contains enough of the metal to make it economic to extract the metal.

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27
Q

How are ores collected and extracted?

A

Ores are mined. Some ores, such as copper ores, need to be concentrated (ground up in to a powder and mixed with water and other chemicals) and purified.

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28
Q

What does it mean for a metal, e.g gold and platinium, to be found in their native state?

A

It means that they don’t need to be extracted from an ore. They are literally found in a pure state.

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29
Q

How does the reactivity series help with extracting metals?

A

It helps decide the best way to extract a metal from its ore.

30
Q

How is the metal within a metal oxide, that is BELOW carbon in the reactivity series, extracted?

A

They can be reduced by carbon (gaining electrons) to give the metal element.

31
Q

How is the metal within a metal oxide, that is ABOVE carbon in the reactivity series, extracted?

A

They cannot be reduced by Carbon. They are extracted by electrolysis of the molten metal compouns. See C6.

32
Q

Summarise how each metal in the reactivity series can be extracted:

A

Above Carbon: (Potassium, Sodium, Calcium, Magnesium, Aluminium) = Electrolysis

Below Carbon up to silver: (Zinc, Iron, Tin, Lead, Copper) = Reduction (removal of oxygen)

Silver, Gold, Platinum = Found in native state (don’t react with the chemicals in the soil and air which once again shows how unreactive they are).

33
Q

How can a salt be formed from a metal?

A

Metal + Acid ———> Salt + Hydrogen

MASH

e.g Fe(s) + 2HCl(aq) ———> FeCl2(aq) + H2(g)

34
Q

Why can Group 1 metals never be used to react with an acid?

A

Because the reaction would be too violent and unsafe.

35
Q

What salts are formed when a metal reacts with the following acids:

HCl - Hydrochloric Acid
H2SO4 - Sulfuric Acid
HNO3 - Nitric Acid

A

HCl - always makes chlorides (containing Cl- ions)

H2SO4 - always makes sulfates (containing SO4 2- ions)

HNO3 - always makes nitrates (containing NO3-ions)

36
Q

If Zinc reacted with nitric acid, the salt formed would be_______.

A

Zinc Nitrate

Zn(NO3)2

You will learn more about the common ions. This will help you with writing the chemical equations for salts and other compounds.

37
Q

What actually is a salt?

A

A salt is a compound formed when the hydrogen in an acid is wholly or partially replaced by metal (or *ammonium) ions.

*Ammonium is an anomoly as it is a non-metal, yet it forms a positive ion, NH4+. Therefore, it can react with an acid to form a salt and hydrogen.

38
Q

How can a pure sample of a salt be taken from the aqueous salt solution?

A

The water can be evaporated, and the salt then crystallises, and can be collected.

39
Q

Why is the reaction between a metal and an acid known as a redox reaction?

A

Because the metal atoms lose electrons (oxidation) and the hydrogen ions from the acid gain electrons (reduction).

40
Q

What is the equation for when a base reacts with an acid?

A

Base + Acid ———> Water + Salt

BAWS

41
Q

What is a base?

A

A base is an insoluble substance that neutralises acids.

Common bases include metal OXIDES and metal CARBONATES.

Metal carbonates however, don’t just produce water and salt. They also produce carbon dioxide.

Metal Carbonate + Acid ———> Water + Salt + Carbon Dioxide

42
Q

How can you work out the formulae of salts?

A

By knowing the charges of the ions.

43
Q

What are the 3 anomolies of simple ion charges that might catch you out?

A

Hydrogen forms H+

Copper forms Cu2+
Zinc forms Zn2+

44
Q

What are the 4 polyatomic ion charges that might catch you out?

A

Ammonium = NH4+

Nitrate = HNO3-

Sulfate = SO4 2-
Carbonate = CO3 2-
45
Q

Use your knowledge of ions to determine the formula of a) Lithium Sulfate and b) Magnesium Bromide:

A

a) Lithium Sulfate:

Lithium is Group 1 so it contains Li+ ions.
Sulfates contain SO4 2- ions.

Lithium needs to lose 1, but sulfate needs to gain 2. So there needs to be 2 Lithium atoms:

Li2SO4

b) Magnesium Bromide

Magnesium = Group 2 so it contains 2+ ions.
Bromide is Group 7 so it contains 1- ions.

Therefore there needs to be 2 bromine atoms:

MgBr2

46
Q

Explain the Required Practical which involves making copper sulfate crystals from copper (II) oxide and sulfuric acid:

A

Aim: To make blue and rhombic copper sulfate crystals from copper (II) oxide and sulfuric acid.

Equipment:

  • Measuring Cylinder
  • 2 Beakers
  • Spatula
  • Filter Funnel and Paper
  • Glass rod
  • Bunsen Burner
  • Evaporating Dish
  • Conical Flask
  • Tongs
  • Sulfuric Acid
  • Copper (II) oxide power

Health and Safety:

  • Wear safety goggles
  • Warm the acid gently
  • Be aware of chemicals

Method:

1) Add insoluble copper oxide to sulfuric acid and stir. Warm gently on a tripod and gauze (do not boil).
2) The solution turns blue as the reaction occurs, showing that the copper sulphate is being formed. Excess black copper oxide can be seen.
3) When the reaction is complete, filter the solution to remove excess copper oxide.
4) Evaporate the water so that the crystals of copper sulfate start to form.

Observations:

When the copper (II) oxide was added, it bubbles in the acid. When the excess copper (II) oxide was added, the liquid became darker. After evaporating the water, we got some blue rhombic crystals.

47
Q

What is the 4th and final way you can make a salt?

A

Acid + Alkali ———> Salt + Water

e.g HCl(aq) + NaOH(s) ———>NaCl(aq) + H2O(l)

AAWS

48
Q

What is an alkali?

A

A soluble base.

Common alkali’s include metal hydroxides (OH- ions) and ammonia (NH3) (don’t confuse with ammonium (NH4+).

49
Q

What is an alkali in relation to an acid?

A

It is the chemical opposite of an acid.

Alkali’s produce OH- ions and acids produce H+ ions.

H+ + OH- ——> H2O

This is why water is formed when an acid reacts with an alkali or a base.

50
Q

What needs to be used so that the reaction between an acid and an alkali can be visible?

A

An acid based indicator.

You can use a titration to see the exact amount of acid or alkali is needed to neutralise the solution.

51
Q

Summarise the 4 Acid Equations that all form salts:

A

1) Metal + Acid ———> Salt + Hydrogen

MASH

2) Base + Acid ———> Water + Salt

Bases include metal oxides and carbonates.

BAWS

3) Carbonate + Acid ———> Water + Carbon Dioxide + Salt

CAWCS

4) Alkali + Acid ———> Water + Salt

Alkali’s are soluble bases and include: hydroxides and ammonia.

AAWS

52
Q

What are Acids?

A

Acids are substances that produce H+ ions, when you add them to water.

53
Q

What are Bases?

A

Bases are insoluble substances that neutralise acid.

54
Q

What is an Alkali?

A

An alkali is a soluble base that is most commonly a hydroxide (OH).

Alkali’s produce OH- ions when you add them to water.

55
Q

What happens when an acid reacts with an alkali?

A

H+ + OH- ——> H2O

This is why water is formed as well as a salt.

56
Q

What is the pH scale?

A

A scale used to show how acidic or alkaline a solution is.

57
Q

What does pH stand for?

A

Power of Hydrogen

58
Q

What are solutions with a pH value less than 7 called?

A

Acidic

59
Q

What are solutions with a pH value more than 7 called?

A

Alkaline

60
Q

What are solutions with a pH value of 7 known as?

A

Neutral

e.g water

61
Q

What colour on the pH scale represents a neutral substance?

A

Green

62
Q

What colour represents a pH of 0 (really strong acid)?

A

Dark Red

63
Q

What colour represents a pH of 14 (really strong alkali)?

A

Dark Purple

64
Q

What is a pH curve?

A

A pH curve is a graph that shows the change in pH when an acid or alkali is added to the other.

65
Q

What will a pH curve look like when acid is gradually added to an alkaline solution?

A

It will start in the top left of the graph and slope down. It will then vertically plummet and in the middle of thos drop is the neutral point. Then the acid will be in excess and the line will curve up near the bottom.

66
Q

What will a pH curve look like when alkali is gradually added to an acidic solution?

A

The line will start near the bottom as the acid is in excess. The line will then suddenly vertically rocket and in the middle of that line will be the neutral point. Then the alkali will be in excess and the line will platto out at the top.

67
Q

What is the best indicator for identifying the pH of certain solutions, out of universal indicator, methyl orange and phenolph-thalein?

A

Universal Indicator as it will shows a wide range of colours.

68
Q

What is the difference between strong acids and weak acids?

A

Aqueous solutions of weak acid such as carboxylic acidS (e.g ethanoic acid - CH3COOH) have a higher pH value than solutions of strong acids with the same concentration.

HCl has a pH of 1.1 (Strong)
CH3COOH has a pH of 3.91 (Weak)

69
Q

As the pH decreases by one unit, how does the hydrogen ion concentration increase by?

A

A factor of 10

1 x 10^-1 (conc of H+ ions in mol/dm^3) = ph of 1.
1 x 10^-2 (conc of H+ ions in mol/dm^3) = ph of 2.
1 x 10^-3 (conc of H+ ions in mol/dm^3) = ph of 3.

What ever the negative power is. The pH value equals the positve number of that.

70
Q

How do strong acids and weak acid react with magnesium (or most metals)?

A

In the strong acid, the magnesium will fizz for many minutes and form a cloudy white solution.

In the weak acid, a cloudy white solution will also be formed. The fizzing will be less violent.

71
Q

How do strong acids and weak acid react with sodium carbonate (or most bases)?

A

In the strong acid, a white powder will form at the bottom, with some fizzing.

In the weak acid, a white powder will also form at the bottom, with less fizzing.

GCSE Chemistry (17 decks)

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