Chemistry Flashcards
(87 cards)
1
Q
Who showed that the plum pudding model was wrong and how?
A
- Ernest Rutherford
- Using the gold foil experiment.
- They fired positively charged particles at a very thin sheet of gold, expecting most of them to be deflected. In reality, very few were.
2
Q
What came as a result of the gold foil experiment?
A
Rutherford suggested the nuclear model of the atom, with a positive nucleus and a cloud of electrons around it.
3
Q
Who refined the nuclear model of the atom proposed by Rutherford and how?
A
- Niels Bohr
- He suggested that the electrons were not in a cloud (which would cause the atom to collapse), but in shells with defined energies.
4
Q
How is copper extracted from its ore?
A
• Copper is displaced from copper sulphate by reacting it with iron.
OR
• Copper is extracted from its ore by heating with carbon, then electrolysis to purify the product.
5
Q
Are the first 3 alcohols soluble?
A
Yes, they dissolve in water to give a neutral solution.
6
Q
What is produced when an alcohol reacts with sodium?
A
Alkoxide + Hydrogen
7
Q
C2H5OH + Na ->
A
2C2H5OH + 2Na -> 2C2H5ONa + H2
8
Q
Name: C2H5ONa
A
Sodium ethoxide (an alkoxide)
9
Q
What are some uses of alcohols?
A
- Solvent -> Dissolves most things that water does, plus hydrocarbons, etc.
- Fuel
10
Q
What is produced when a carboxylic acid reacts with a carbonate?
A
- Salt
- Carbon dioxide
- Water
11
Q
What are the name endings for the salts produced by carboxylic acid reactions?
A
- oates
e. g. sodium ethanoate
12
Q
Ethanoic acid + Sodium carbonate ->
A
Ethanoic acid + Sodium carbonate -> Sodium ethanoate + Carbon dioxide + Water
13
Q
Give some examples of common carboxylic acids.
A
- Citric acid
* Ethanoic acid (vinegar)
14
Q
How can ethanoic acid be produced?
A
- Oxidising ethanol using microbes (like yeast).
* Ethanol + Oxygen -> Ethanoic acid + Water
15
Q
Give a use of ethanoic acid.
A
- Vinegar (when dissolved in water)
* Solvent (although it makes the solution acidic)
16
Q
Give a use of citric acid.
A
- Fizzy drinks
* Scale removal
17
Q
Give some general uses of carboxylic acids.
A
- Soap
* Preparations of esters
18
Q
Give the state and colour of flourine.
A
Yellow gas
19
Q
Give the state and colour of chlorine.
A
Green gas
20
Q
Give the state and colour of bromine.
A
Red-brown liquid
21
Q
Give the state and colour of iodine.
A
Dark grey solid
22
Q
Give some uses of argon.
A
- Inert atmosphere in lightbulbs
* Protection for metals being welded
23
Q
Give some uses of helium.
A
- Party balloons
* Airships
24
Q
What is another name for a giant covalent structure?
A
Macromolecule
25
What are some uses of transition metals?
Usually used as catalysts.
26
What do compounds of transition metals usually look like?
Colourful
27
Remember to revise the hazard symbols.
Pg 137.
28
What is the difference between acid strength and acid concentration?
* Acid strength - The proportion of acid molecules that ionise in water.
* Acid concentration - How many moles of acid there are per volume of water.
29
What is a better conductor: strong or weak acid?
Strong acid
30
What does the electrolysis of an acid produce?
Hydrogen gas
31
How can you test for some metal ions without a flame test?
* Add NaOH
* Look for a coloured precipitate (metal hydroxide)
* The colour identifies the metal ion
32
What colour is calcium hydroxide? (Ca2+)
White
33
What colour is copper hydroxide? (Cu2+)
Blue
34
What colour is iron(II) hydroxide? (Fe2+)
Green
35
What colour is iron(III) hydroxide? (Fe3+)
Brown
36
What colour is aluminium hydroxide? (Al3+)
White
| NB: redissolves in excess NaOH though
37
What colour is magnesium hydroxide? (Mg2+)
White
38
In metal ion precipitation tests, how can you tell apart aluminium hydroxide from the other white precipitates?
Aluminium hydroxide redissolves in excess NaOH to give a colourless solution.
39
What are the two phases of chromatography?
* Mobile phase
| * Stationary phase
40
Explain the concept of phases in chromatography.
* The mobile phase is usually a liquid or gas in which the molecules of the substance can move.
* The stationary phase is usually a solid in which the molecules of the substance cannot move.
* Molecules of the substance can move between phases until they reach an equilibrium -> The position depends on the solubility of the substance in that solvent.
41
Give an example of the mobile and stationary phase.
* Mobile - Solvent such as ethanol
| * Stationary - Paper
42
Describe paper chromatography in detail.
1) A spot of the substance is placed on a baseline on the paper (stationary phase).
2) This is placed in a beaker with solvent (mobile phase).
3) Solvent moves up the paper.
4) The chemicals in the substance dissolve in the solvent. This sets up an equilibrium between the phases.
5) When a molecule is in the mobile phase, it moves up with the solvent.
6) So the more time a chemical spends in the mobile phase, the further up the paper it will travel.
7) Before the solvent reaches the top of the paper, it is removed from the beaker.
43
What things can affect how long a chemical spends in the mobile phase?
* Solubility in the solvent
| * Attraction to the stationary phase (e.g. paper)
44
Name two types of chromatography.
* Paper chromatography
| * Thin-layer chromatography (TLC)
45
What is TLC chromatography?
* Thin-layer chromatography
* It is like paper chromatography, but the stationary solvent is a thin layer of solid (e.g. silica gel spread on a plate)
* The mobile phase is a solvent, just like in paper chromatography
46
How can the purity of an isolated substance be improved?
Repeating the isolation process (e.g. filtration, evaporation, crystallisation)
47
Give 2 examples when the purity of an isolated substance is important.
1) Pharmaceuticals - Impurities could do humans harm
| 2) Petrochemicals - Impurities could do engine damage
48
Describe how you can calculate the purity of an isolated substance.
1) Do a titration to work out the mass of the pure isolated substance that must be reacting.
2) Compare this to the actual mass of the impure isolated substance.
3) Work out a percentage purity.
49
What is electroplating?
The use of electrolysis to coat the surface of a metal with another metal.
50
Describe how electroplating works.
* Negative electrode is the object to be coated, while positive electrode is the pure metal to coat it with. Electrolyte must also contain the plating metal.
* This forms an electrolysis circuit.
* This causes the plating metal to lose electrons, travel across the chamber, gain electrons at the negative electrode and be deposited there.
51
What is each electrode made of in electroplating?
* Negative electrode (cathode) -> Object to be coated
| * Positive electrode (anode) -> Plating metal
52
Explain how you could electroplate a brass cup in silver.
* Make the brass cup the negative electrode
* Make a piece of silver the positive electrode
* Make a silver nitrate solution the electrolyte
53
Explain how you could electroplate a metal in copper.
* Make the metal the negative electrode
* Make a piece of copper the positive electrode
* Make a copper sulphate solution the electrolyte
54
What is hardness of water?
The amount of dissolved calcium and magnesium in water.
55
What are the main problems of hard water?
* Scum
| * Scale
56
Explain how hard water leads to scum and why this is a problem.
* Magnesium and calcium in the water react with the soap to give scum
* This scum is insoluble
* Therefore, more soap has to be used to get a good lather, which is expensive
57
Explain how hard water leads to scale and why this is a problem.
* Boiling hard water leads to the deposition of scale in pipes, kettles and boilers.
* This reduces the efficiency of these devices and can block them.
58
What is scale?
Mostly calcium carbonate
59
How does scale affect devices?
* Scale can block pipes
| * Scale is a thermal insulator, so it can reduce the efficiency of heating devices
60
What ions tend to cause hard water?
Ca2+ and Mg2+
61
Describe how hard water can be formed.
Rain falling on certain rocks can dissolve compounds like:
• Calcium sulfate
• Magnesium sulfate
62
Give 2 benefits of hard water.
* Ca2+ ions are good for strong teeth and bones
| * Minerals in the water may reduce the risk of heart disease
63
What are the two types of water hardness?
* Temporary
| * Permanent
64
What is temporary hardness caused by?
Hydrogencarbonate ions HCO3- in Ca(HCO3)2
65
What is permanent hardness caused by?
Dissolved calcium sulphate (amongst other things)
66
How can temporary hardness of water be removed?
* Boiling -> Calcium hydrogencarbonate decomposes to insoluble calcium carbonate
* Add washing soda (sodium carbonate) -> Carbonate ions react with Ca2+ to give insoluble CaCO3
* Ion exchange column -> Sodium or hydrogen ions are exchanged for the Ca2+ ions
67
How can permanent hardness of water be removed?
* Add washing soda (sodium carbonate) -> Carbonate ions react with Ca2+ to give insoluble CaCO3
* Ion exchange column -> Sodium or hydrogen ions are exchanged for the Ca2+ ions
68
What two methods of removing hardness of water work for both temporary and permanent hardness?
* Add washing soda (sodium carbonate) -> Carbonate ions react with Ca2+ to give insoluble CaCO3
* Ion exchange column -> Sodium or hydrogen ions are exchanged for the Ca2+ ions
69
Explain how boiling water can be used to remove temporary hardness.
* Calcium hydrogencarbonate decomposes into insoluble calcium carbonate, which forms solid limestone, leaving no ions in the water
* Calcium hydrogencarbonate -> Calcium carbonate + Carbon dioxide + Water
* Ca(HCO3)2 -> CaCO3 + CO2 + H2O
70
What is the limescale on your kettle and what causes it?
Calcium carbonate, deposited when temporarily hard water is boiled.
71
Why can permanent hardness of water not be removed by boiling?
Calcium sulphate does not decompose easily on heating.
72
Explain how adding washing soda can be used to remove hardness of water.
* Carbonate ions in the washing soda (sodium carbonate) react with Ca2+ and Mg2+ ions in the water, which causes an insoluble solid to form
* Ca2+ + CO3 2- -> CaCO3
73
Explain how an ion exchange column can be used to remove hardness of water.
* Column has lots of sodium or hydrogen ions, which can be used to 'exchange' calcium or magnesium in the water
* Na2(Resin) + Ca2+ -> Ca(Resin) + 2Na+
74
Describe an experiment to compare the hardness of several samples of water.
* Put 50cm3 of soap solution in a burette
* Put 50cm3 of the first water sample in a flask
* Keep adding 1cm3 of the soap solution to the water and then shaking to try and get a good lather
* Do this until the bubbles on the surface stay for at least 30 seconds
* Record this volume of soap and then repeat with all the different water samples, both boiled and not boiled
75
Is the reaction between hydrogen and water exothermic or endothermic?
Exothermic
76
Describe the energy level diagram for hydrogen reacting with water.
* Starting line with H2 and O2
* Middle line above the starting line with H and O
* End line below the starting line with H2O
77
What is a fuel cell?
An electrical cell that's supplied with oxygen and fuel, which it uses to produce electrical energy.
78
Give an example of a fuel cell.
A hydrogen-oxygen fuel cell.
79
What does a hydrogen-oxygen fuel cell produce?
* Heat energy
| * Water
80
What is the advantage of a hydrogen-oxygen fuel cell?
It does not produce any pollutants.
81
What type of reaction does a hydrogen-oxygen fuel cell involve?
Redox
82
Describe how a hydrogen-oxygen fuel cell works.
1) Electrolyte is potassium hydroxide
2) Hydrogen goes into anode compartment and anode goes into cathode compartment
3) At the cathode, oxygen gains electrons and reacts with the water in the electrolyte to make OH- ions
O2 + 4e- + 2H2O -> 4OH-
4) At the anode, the hydrogen reacts with the OH- to give water and electrons
2H2 + 4OH- -> 2H2O + 4e-
5) Current flows through an external circuit from anode to cathode
83
What is the overall equation for the reaction in a hydrogen-oxygen fuel cell?
2H2 + O2 -> H2O
84
What happens at the anode in a hydrogen-oxygen fuel cell?
* Hydrogen is oxidised by losing electrons
* Then it combines with OH- ions to give water and electrons
* 2H2 + 4OH- -> 2H2O + 4e-
85
What happens at the cathode in a hydrogen-oxygen fuel cell?
* Oxygen is reduced by gaining electrons
* Then it reacts with water (from the electrolyte) to make OH- ions
* O2 + 4e- + 2H2O -> 4OH-
86
Give half and overall equations for what is happening in a hydrogen-oxygen fuel cell.
Cathode: O2 + 4e- + 2H2O -> 4OH-
Anode: 2H2 + 4OH- -> 2H2O + 4e-
Overall: 2H2 + O2 -> H2O
87
Remember to revise the diagram for the hydrogen-oxygen fuel cell.
Pg 188.
