Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

chemistry > C4 (chemical changes) > Flashcards

C4 (chemical changes) Flashcards

1
Q

what happens when metals react with oxygen?

A
  • when metals react with oxygen, they form a metal oxide.
  • the metal atoms are oxidised (gains oxygen).
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is an oxidation reaction (includes oxygen)?

A

an element (usually a metal) gaining oxygen is called an oxidation reaction.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what is a reduction reaction (includes oxygen)?

A

an element (usually a metal) losing oxygen is called a reduction reaction.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what happens when you react a metal with water?

A

reacting a metal with water produces a metal hydroxide and hydrogen gas.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what occurs when metals react?

A
  • they lose electrons and form a positive ion.
  • the reactivity of a metal depends on its ability to lose electrons and form an ion. (i.e. potassium is more reactive and is more able to form a positive ion. copper is less reactive and the least able to form a positive ion).
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

how are different metals found in the Earth, based on their reactivity?

A
  • unreactive metals, such as gold, are found in the Earth as the metal itself.
  • most metals aren’t found pure. more reactive metals (e.g. iron), are found to have reacted with oxygen in the Earth’s crust, to form a compound (e.g. a metal oxide, iron oxide)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what is an ore?

A

a metal that can be extracted from a rock for profit.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is a displacement reaction?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what is an oxidation reaction (involves electrons)?

A

the loss of electrons.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is a reduction reaction (involves electrons)?

A

the gain of electrons.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what is a redox reaction?

A

a reaction where both oxidation and reduction (in terms of electrons) occur at the same time.

  • this is what occurs usually, as if one substance loses electrons, another has ro gain them.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is the valence electron?

A

the outermost electron(s)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what are similarities amongst all acids?

A
  • common acids include hydrochloric acid, sulfuric acid and nitric acid.
  • all acids contain hydrogen (acid molecules ionise - split - and release H+)
  • they’re all aqueous (can be dissolved in water).
  • an H⁺ ion is an acid.
  • they all have a pH less than 7.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what occurs when an acid reacts with a metal?

A

acid + metal = salt + hydrogen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what occurs when an acid reacts with a metal oxide/metal hydroxide?

A

metal oxide/hydroxide + acid = salt + water

  • we take the negative ion from the acid, and combine it with the positive ion from the base, to create a salt. the leftover is then water.

THIS IS A NEUTRALISATION REACTION.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what occurs when an acid reacts with a metal carbonate?

A

metal carbonate + acid = salt + water + CO₂

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

how would you create a soluble salt?

A

react an acid with an insoluble base (e.g. metal oxide/hydroxide/carbonate)

THIS IS A NEUTRALISATION REACTION.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

how do hydrochloric acid and sulfuric acid react with metals?

A

hydrochloric acid produces salts that end with ‘-chloride’.

sulfuric acid produces salts that end with ‘-sulfate’.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

how do magnesium, zinc and iron react with acids?

A

magnesium = rapid reaction. much higher than hydrogen on the reactivity series, so displacement is easier.

zinc = quite a rapid reaction. quite a bit higher than hydrogen, so displacement is also relatively easy.

iron = fairly slow reaction. it’s only one higher than hydrogen on the reactivity series, so displacement won’t be as easy.

20
Q

what are similarities amongst all hydroxides (alkalis)?

A
  • common hydroxides include sodium hydroxide, potassium hydroxide and calcium hydroxide.
  • all include hydrogen and oxygen.
  • an OH⁻ ion is an alkali.
21
Q

describe methyl orange, universal indicator and phenolphthalein:

A

methyl orange: red = acid, orange = alkali
phenolphthalein: clear = acid, pink = alkali
universal indicator: a mix of different indicators, giving a bright range of colours.

22
Q

what is a base?

A

a base is a substance that, when dissolved in water, can produce OH⁻ (hydroxide) ions. not all bases are soluble.
- when dissolved, the solution is an alkali.
- metal oxides (e.g. FeO) are basic, and when dissolved, can produce OH⁻ ions (though not all can dissolve).

23
Q

what is the pH scale?

A

from 0-14, it’s a measure of how the acidity/alkalinity of a solution. it can be measured using universal indicator.

  • a solution with a pH of 7 is neutral.
  • aqueous solutions of acids have pH values of less than 7.
  • aqueous solutions of alkalis have pH values of more than 7.
24
Q

what is a strong acid?

A
  • examples include: hydrochloric acid, sulfuric acid, and nitric acid.
  • when dissolved in water, strong acids fully ionise ( all hydrogen ions disassociate).
  • in symbol equations, the arrow will only point one way.
25
Q

what is a weak acid?

A
  • examples include carbonic acid, ethanoic acid, citric acid.
  • when dissolved in water, weak acids only partially ionise. only some hydrogen ions disassociate.
  • it can be recognised in symbol equations by arrows pointing both ways - it’s a reversible reaction.
26
Q

how can the pH scale be used in terms of strong and weak acids?

A
  • the pH scale gives us an idea of the concentration of hydrogen ions.
  • strong acids have a lower pH than weak acids for a given concentration. this is because strong acids full ionise, producing a greater concentration of hydrogen ions than weak acids, which only partially ionise.
  • AS THE pH SCALE DECREASES BY 1 UNIT, THE CONCENTRATION OF HYDROGEN IONS INCREASES BY 10X. (pH 1 has a 10x greater concentration of hydrogen ions than pH 2. this is ONE ORDER OF MAGNITUDE).
27
Q

can solid ionic compounds conduct electricity?

A

they cannot conduct electricity, as the ions are locked in place (by strong electrostatic forces of attraction) and are not free to move to carry the electric charge.

  • however, when an ionic compound is melted or dissolved, the electrostatic forces are broken, and the ions are free to move. they can now conduct electricity, and are considered ELECTROLYTES.
28
Q

describe the electrolysis of molten lead bromide:

A
  • there are 2 electrodes, made of a conducting material (e.g. graphite or a metal).
  • the negative electrode is called the cathode. it’s attached to the negative terminal of a powerpack. this is covered with electrons.
  • the positive electrode is called the anode. it’s attached to the positive terminal of a powerpack. this lacks electrons.
  • the molten lead bromide solution surrounds the two cathodes. the positive lead ions are attracted to the negative cathode - opposite charges attract. the lead ions now gain two electrons to form lead atoms (REDUCTION REACTION).
  • the negative bromide ions are attracted to the positive anode. here, they lose one electron to form bromine atoms. (OXIDATION REACTION).
29
Q

what is the purpose of electrolysis?

A

to separate the elements in insoluble ionic compounds.

30
Q

what is an electrolyte?

A

a liquid or solution that contains an ionic compound. as it is in liquid form, the ions are free to move (in this case, to each electrode).

31
Q

how do we extract certain metals on the reactivity series?

A
  • zinc, iron, copper, and any other elements lower down the series than carbon can be extracted using carbon, as it’s inexpensive.
  • any elements above carbon must be extracted using electrolysis, as any other way would be too expensive.
32
Q

describe the electrolysis of aluminium oxide:

A
  1. aluminium oxide is mixed with the compound, cryolite, lowering its melting point (reduces amount of energy needed, saves money).
  2. apply an electric current to the molten aluminium oxide.
  3. the cathode and anode are both made of graphite (a form of carbon. good conductor of electricity, high melting point).
  4. the aluminium ions and oxide ions are free to move in the electrolyte, as the ionic compound is molten.
  5. the aluminium ions are attracted to the cathode, and form aluminium atoms. REDUCTION REACTION.
  6. the oxide ions are attracted to the anode, and form oxygen atoms.
33
Q

what is the half equation for the reduction reaction of aluminium at the cathode during electrolysis?

A

Al³+ + 3e- = Al

34
Q

what is the half equation for the oxidation reaction of oxygen at the anode during electrolysis?

A

2O²- = O₂ + 4e-
OR
2O²- - 4e- = O₂

35
Q

why must the anode be replaced regularly?

A

the oxygen molecules produced at the anode react the graphite (carbon), forming carbon dioxide gas. this can wear away at the electrode, damaging it.

36
Q

why is electrolysis so expensive?

A
  • melting compounds (i.e. aluminium oxide) requires a great deal of energy.
  • a lot of energy is required to produce an electric current.
37
Q

what occurs during the electrolysis of copper sulfate solution (an aqueous solution)?

A

in the electrolyte, a copper ion, a sodium ion, a hydrogen, and a hydroxide ion will be present.

(hydrogen and hydroxide ions are produced when water molecules ionise (split))

38
Q

how do we know whether the hydrogen or copper ion will be attracted to the cathode in the electrolysis of copper sulfate solution?

A

hydrogen is produced at the cathode if the metal is more reactive than hydrogen.

as copper sulfate is lower down the reactivity series than hydrogen, copper is produced at the cathode, instead of hydrogen.

oxygen gas will be made at the anode.

39
Q

what metal is often used as the electrode in the electrolysis of aqueous solutions?

A

platinum is often used as the metal for electrodes, as it is inert (unreactive).

40
Q

what is usually produced at the anode in the electrolysis of an aqueous solution?

A

oxygen is usually produced at the anode (from hydroxide ions), but there is an exception. if the other ions are halide, then they will be produced instead.

41
Q

how do we know what will be produced at the anode during the electrolysis of aqueous solutions?

A

if the aqueous solution contains halide ions, then the halogen will be produced at the anode.
- for example, if it was between chlorine and hydroxide, then chlorine ions would be produced at the anode, as they are halide ions.

42
Q

what is a halide ion?

A

a halogen atom with a negative charge (a halogen ion).

43
Q

what is the half equation at the cathode during the electrolysis of copper sulfate solution?

A

Cu²+ + 2e- = Cu

REDUCTION REACTION

44
Q

what is the half equation at the anode during the electrolysis of copper sulfate solution?

A

4OH- = O₂ + 2H₂O + 4e-
OR
4OH- - 4e- = O₂ + 2H₂O

OXIDATION REACTION.

45
Q

how do you write the half equation for an element in a reaction?

A
  1. copy out the ionic equation, but only for one particular element.
    > change: Ca + Fe²+ = Ca²+ + Fe
    to: Ca = Ca²+
  2. add electrons, to make the charges balance.
    > as calcium loses two electrons, we
    can think of the calcium ion as one
    product, and the two electrons as
    another product.
    > this makes: Ca = Ca²+ + 2e-

chemistry (6 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions