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Chemistry > Chemical Changes > Flashcards

Chemical Changes Flashcards

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1
Q

What happens when you react a metal with water

A
  • it produces a metal hydroxide which is an alkali and hydrogen gas
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2
Q

What determines how rapidly a metal reacts (key facts about reactive metals)

A
  • when metals react, they lose electrons and form a positive ion
  • the reactivity of a metal depends on its ability to lose electrons and form a positive ion (the higher the reactivity the more likely it is)
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3
Q

Key fact about acids

A

All acids contain hydrogen

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4
Q

What products form when reacting an acid and a metal

A

A salt and hydrogen gas

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5
Q

What does the salt produced depend on

A

The acid used and the metal that it’s reacting with

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6
Q

How do three different metals (magnesium, zinc and iron) react with the acids hydrochloric acid and sulfuric acid

A
  • magnesium reacts rapidly with acids as it is quite a lot more reactive than hydrogen, so can easily displace hydrogen from acids
  • zinc reacts quite rapidly with acids as it is more reactive than hydrogen, and can easily displace hydrogen from acids
  • iron reacts fairly slowly with acids, although it is more reactive than hydrogen it is only a slight difference so will be a slow reaction
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7
Q

What salts does hydrochloric acid produce

A

Salts that end in the word -chloride

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8
Q

What salts do sulphuric acid produce

A

Salts that end in the word -sulfate

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9
Q

What are bases and what are alkalis

A
  • bases are chemicals which can neutralise acids and produce a salt and water
  • alkalis are bases that are soluble in water
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10
Q

What happens when we react an acid with a base or an alkali

A

We make a salt and water

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11
Q

Key facts about salts

A
  • contain a positive ion which comes from the base or alkali

- contain a negative ion which c9mes from the acid

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12
Q

What does hydrochloric acid, sulfuric acid and nitric acid produce

A
  • chlorides
  • sulfates
  • nitrates
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13
Q

Predict the products of the following reaction.

Nitric acid + Lithium hydroxide ——>

A

———> lithium nitrate + water

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14
Q

What do acids produce when they react with a metal carbonate

A

A salt, water and carbon dioxide

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15
Q

Predict the products of the following reaction.

Hydrochloric acid + copper carbonate ——>

A

——-> copper chloride + water + carbon dioxide

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16
Q

What substances would you react to make magnesium nitrate

A

Nitric acid + magnesium hydroxide —> magnesium
(has to be compound) nitrate
+ water

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17
Q

What are the soluble salts

A

S odium Na
N itrate No
A mmonium NH
P otassium K

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18
Q

How can soluble salts be made

A

-by reacting acids with either soluble or insoluble bases

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19
Q

How would you make the soluble salt (in a practical)

A
  • start with fixed volume of dilute sulfuric acid, our limiting reactant (the acid will run out)
  • heat acid until almost boiling
  • use spatula to add small amounts of copper oxide to acid
  • stir solution with glass rod
  • the copper oxide will react and seem to disappear
  • continue adding copper oxide until the powder remains after stirring
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20
Q

Why would you not want any acid remaining at the end (making soluble salts)

A

It would contaminate the salt

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21
Q

What do you do if the solution continues to be a clear blue colour after the copper oxide has reacted

A

Continue adding copper oxide and stop if some powder remains after stirring

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22
Q

How to remove the uncreated copper oxide

A
  • use filtration to remove unreacted copper oxide
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23
Q

How do you make crystals from the salt

A
  • place solution in evaporating basin
  • heat over a beaker of boiling water
  • heat until half of solution remains
  • leave solution for 24 hours in cool place for crystals to form
  • scrape crystals on paper towel and pat dry
24
Q

Key fact about acids

A

They produce hydrogen ions in aqueous solutions

25
Q

Key fact about alkalis

A

Aqueous solutions of alkalis contain hydroxide ions

26
Q

What does the pH scale tell us and how do we determine the pH

A
  • The acidity or alkalinity of a solution

- we determine the pH using a pH probe (electronic) or a universal indicator (changes colour)

27
Q

What do the colours on the pH scale mean

A
  • green shows a neutral solution
  • colours towards red show acidic solutions
  • colours towards purple show alkaline solutions
28
Q

What pH do acids and alkaline have

A
  • a pH of less than 7 is acidic
  • a pH of 7 are neutral
  • a pH of 8-14 are alkaline
29
Q

What is the equation for neutralisation

A

H + OH ———> H2O
Hydrogen Hydroxide Water
ion ion
(Acid) (Alkali)

30
Q

What do strong acids do and what do they have

A
  • Strong acids fully ionise (split) in aqueous solutions

- they have lower pH than weak acids for a given concentration

31
Q

What do acids do in aqueous solutions

A

The acid molecules ionise (split) and release H+

32
Q

What are the strong acids

A
  • hydrochloric acid
  • sulfuric acid
  • nitric acid
33
Q

What do weak acids do

A

They partially ionise in aqueous solutions

34
Q

How can you tell if there is a weak acid

A

There is a reversible reaction sign (looks like two arrows going opposite ways)

35
Q

What are the weak acids

A
  • carbonic acid
  • Ethan oil acid
  • citric acid
36
Q

What does the pH scale do (in terms of strong and weak acids)

A

Gives us the idea of the concentration of hydrogen ions produced by acids

37
Q

Why do strong acids have a lower pH than weak acids for a given concentration

A
  • strong acids fully ionise producing a greater concentration of hydrogen ions than weak acids (which are only partially ionised)
38
Q

What happens when the pH scale decreases by one unit

A

- The concentration of hydrogen ions increases by ten times (one order of magnitude)

  • (eg pH 1 has a ten times greater concentration than pH 2)
  • (eg 2, pH 1 has an 100x greater concentration of H than pH 3 which is two orders of magnitude)
39
Q

What does the concentration of acids tell us

A
  • The concentration of an acid tells us the amount of acid molecules in a given volume of solution
  • a dilute solution will have fewer acid molecules in a given volume than a concentrated acid even if the strength of the acid is the same
40
Q

What is an oxidation reaction

A
  • when atoms (eg Mg) loses electrons

- the (Mg) atoms are being oxidised

41
Q

What is reduction

A
  • when ions (eg hydrogen) gain electrons

- the hydrogen ions are being reduced

42
Q

What is happening in this reaction

Fe —-> Fe2+ + 2e-

2H+ + 2e- —-> H2

A
  • the iron atoms are being oxidised as they’re losing electrons (oxidation)
  • the hydrogen ions from the acid are gaining these electrons and are being reduced (reduction)
43
Q

What are the rate of reactions with dilute acids for magnesium, zinc and iron

A

Magnesium- very rapid reaction (easily forms Mg2+)
Zinc- quite rapid reaction (quite easily forms Zn2+)
Iron- slow reaction (less easily forms Fe2+)

44
Q

Key facts about electrolysis

A
  • solid ionic compounds cannot conduct electricity as the ions are locked in place and are not free to move
  • when an ionic compound is melted or dissolved in water, the forces of attraction are broken and the ions are free to move (the liquids and solutions can now conduct electricity)
  • these liquids or solutions are called electrolytes
45
Q

What happens when we carry out electrolysis on a molten ionic compound such as lead bromide

A
  • Pb2+ ions are attracted to the negative electrode as opposite charges attract
  • the Pb2+ ions gain two electrons to form Pb atoms (reduction)
  • the Br- ions are attracted to the positive electrode
  • they lose one electron to form Br atoms (oxidation)
46
Q

What does molten mean

A

Melted

47
Q

What is the negative electrode and the positive electrode

A
  • the cathode (negative electrode) is covered with negative electrons coming from the power pack
  • the anode (the positive electrode) has a lack of electrons
48
Q

What is an exothermic reaction

A
  • they transfer energy from the reacting molecules to the surroundings
  • the temperature of the surroundings increases
  • examples include combustion (burning), oxidation reactions and neutralisation
49
Q

What can you notice in an energy profile for an exothermic reaction

A
  • the products have less energy than the reactants as energy has been transferred from the reaction to the surroundings
50
Q

What does the difference between the energy of the reactants and the energy of the products tell us in an exothermic reaction

A

The energy that has been released to the surroundings

51
Q

How can exothermic reactions be useful

A
  • hand warmers

- self heating cans eg for food and drink

52
Q

What do endothermic reactions do

A
  • they take in energy from their surroundings
  • the temp of the surroundings decreases (colder)
  • an example of endothermic reactions is thermal decomposition
53
Q

What can you notice in an energy profile for endothermic reactions

A

The products have more energy than the reactants as the energy has been taken in from the surroundings

54
Q

What does the difference in energy between the reactants and the products tell us in an endothermic reaction

A

The amount of energy that has been taken in by the reaction

55
Q

What do the energy profiles for endothermic and exothermic reactions have in common

A
  • in both cases the energy rises to a peak (the activation energy)
56
Q

What are the key ideas about activation energy

A
  • the reactions can only occur when the particles collide with each other
  • the minimum amount of energy that particles must have in order to react is called the activation energy
  • on an energy profile diagram the activation energy is from the reactants to the peak of the curve

Chemistry (5 decks)

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