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Flashcards in chem 6 Deck (43)
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1
Q

What is a solvent?

A

A liquid that will dissolve a solid.

2
Q

What is a redox reaction?

A
  • when electrons are transferred
  • loss of electrons is oxidation
  • gain of electrons is reduction
3
Q

What is a displacement reaction?

A
  • a more reactive metal will displace a less reactive metal from its compound
  • the metal ION always gains electrons and is reduced
  • the metal ATOM always loses electrons and is oxidised
4
Q

what is the word equation for rusting of iron?

A

Iron+oxygen+water->hydrated iron(III) oxide

5
Q

Why is rusting of iron a redox reaction?

A
  • iron loses electrons when it reacts with oxygen, each Fe atom loses 3 electrons to become Fe3+. Irons oxidised
  • oxygen gains electrons when it reacts with iron, each O atom gains 2 electrons to become O2-. Oxygens reduced
6
Q

How can you prevent rusting?

A
  • iron can become an alloy by mixing it with other metals such as carbon
  • by coating the iron with a barrier of paint or oil or grease
  • by tin plating, acts as barrier stopping water and oxygen reaching surface of iron
7
Q

What is the sacrificial method used to stop iron rusting?

A
  • you place a more reactive metal with iron so water and oxygen react with that instead of iron
  • galvanising is a coat of zinc
  • blocks of magnesium can be bolted to iron
8
Q

What is electrolysis?

A
  • breaking down of a substance using electricity
  • electric current is passed through dissolved ionic compound, causing it to decompose
  • this creates flow of charge through electrolyte
  • positive ions in solution will go to cathode and gain electrons
  • negative ions in solution go to anode and lose electrons
9
Q

What happens at the cathode and anode with a molten electrolyte of lead iodide, Pbl2?

A
Cathode:
-lead produced
-Pb2+ +2e-->Pb
Anode:
-iodine produced
-2l->l2+2e-
10
Q

What happens at the cathode and anode with a molten electrolyte of potassium chloride, KCl?

A
Cathode:
-potassium produced 
-K+ + e- -> K
Anode: 
-chlorine produced
-2Cl- ->Cl2 +2e-
11
Q

What happens at the cathode and anode with a molten electrolyte of aluminium oxide, Al2O3?

A
Cathode:
-aluminium produced
-Al3+ + 3e- ->Al
Anode: 
-oxygen
-202- -> O2 + 4e-
12
Q

What does the amount of product made during electrolysis depend on and how can you increase it?

A
  • the number of electrons that are transferred

- can be increased by electrolysing for a longer time and increasing the current

13
Q

What is the equation to work out the amount of product formed during electrolysis?

A

Q=It
Charge=current x time
They are directly proportionate

14
Q

What are fuel cells?

A

-electrical cells that combine hydrogen and oxygen to give out energy in an exothermic reaction

15
Q

What is the equation at the anode and cathode and overall for the redox reaction of fuel cells?

A
Cathode: reduction
-O2+4e-+2H2O-> 4OH-
Anode: oxidation 
-2H2+4OH- -> 4H2O+4e- 
Overall: redox
-2H2+O2-> 2H2O
16
Q

What are the advantages of fuel cells?

A
  • more efficient than power stations
  • direct energy transfer
  • fewer places for energy to be lost as heat
  • energy isn’t lost through friction
  • no pollution
17
Q

What are disadvantages to fuel cells?

A
  • energy to produce hydrogen may come from non renewable fossil fuels
  • often contain poisonous catalysts which eventually have to be disposed off which is expensive and may cause environmental problems
18
Q

Why are hydrogen-oxygen fuel cells used in spacecraft?

A
  • readily available from the spacecraft rocket fuel tanks
  • lightweight and compact so they don’t take up valuable room
  • don’t have moving parts that could go wrong
  • some product of reaction is used as drinking water
19
Q

Why are fuel cells used in the car industry?

A
  • don’t produce carbon dioxide, nitrogen oxides, sulfur dioxide, carbon monoxide
  • large amounts available for use as a fuel
20
Q

Why did scientists believe CFCs were good at first?

A
  • non toxic, non flammable and chemically inert, insoluble and low boiling points
  • used as coolants in fridges and air con
  • used as propellants in aerosol spray cans
21
Q

How do scientists discover the truth about CFCs?

A
  • chlorine can help destroy ozone
  • evidence of decreasing ozone levels over Antarctica
  • measurements in upper atmosphere showed high levels of compounds produced by breakdown of CFCs
22
Q

What is ozone?

A
  • form of oxygen with formula O3
  • found in stratosphere
  • absorbs UV light from sun and breaks it down to oxygen molecule and atom, O3+UV->O+O2
  • the oxygen molecule and atom join together to make ozone again, O+O2->O3
23
Q

How do chlorine free radicals from CFCs damage the ozone layer?

A
  • UV light makes carbon-chlorine bonds in CFCs break down to form free radicals, CCl2F2->CClF2•+Cl•
  • chlorine free radicals race with ozone turning it into oxygen and chlorine oxide, O3+Cl•->ClO•+O2
  • chlorine oxide is very reactive and reacts with ozone to make 2 oxygen molecules and another free radical, ClO•+O3->2O2+Cl•
24
Q

What are safer alternatives to CFCs?

A
  • alkanes

- hydrofluorocarbons

25
Q

What does hard water do?

A
  • form lime scale inside pipes, kettles and boilers which can block pipes
  • doesn’t lather easily with soap, makes scum instead
26
Q

What is hard water caused by?

A
  • calcium ions and magnesium ions
  • as water flow as over rocks and through soils containing Ca2+ and Mg2+, they dissolve in it
  • rainwater is slightly acidic and reacts with calcium carbonate to form calcium hydrogen carbonate
27
Q

What is the overall equation for creating hard water?

A

Carbon dioxide+water+calcium carbonate -> calcium hydrogencarbonate

28
Q

How can you remove temporary hardness from water?

A
  • by boiling
  • calcium hydrogencarbonate decomposes to form insoluble CaCO3
  • calcium hydrogencarbonate-> calcium carbonate+water+carbon dioxide
29
Q

How can you remove permanent hardness of water?

A

-adding washing soda, sodium carbonate
-carbonate ions join into calcium ions and make insoluble precipitate of calcium carbonate
>can also be removed by ion exchange resin

30
Q

What is the method to compare hardness of water samples?

A
  • add 100cm3 water to conical flask
  • add 1cm3 soap solution and shake
  • repeat till good lasting lather is formed
  • record how much soap was needed
31
Q

What is the general formula for an alcohol?

A

CnH2n+1OH

32
Q

How is ethanol formed using fermentation?

A

Glucose->ethanol+carbon dioxide

C6H12O6->2C2H5OH+2CO2

33
Q

How can ethanol be made by hydrating ethene?

A
  • ethene reacts with steam to make ethanol
  • needs temperature of 300 degrees and pressure of 70 atmospheres
  • phosphoric aid catalyst is used
  • C2H4+H2O->C2H5OH
34
Q

Compare the fermentation and hydration methods of producing ethanol

A

Manufacture- fermentation is batch process and slow, hydration is continuous and fast but expensive
Sustainability-fermentation makes renewable fuel, hydration does not
Purity- fermentation isn’t very pure but hydration is
Atom economy- fermentation has lower atom economy
Percentage yield-hydration is better than fermentation

35
Q

What type of emulsions are milk and butter?

A

Milk- oil-in-water emulsion, oil droplets are suspended in water meaning there’s less oil than water
Butter- water-in-oil emulsion, water droplets are suspended in oil meaning there’s more oil than water

36
Q

How can vegetable oils produce biodiesel?

A
  • rapeseed oil and soybean oil can be processed and turned into fuels
  • vegetable oil provides a lot of energy
37
Q

How are fats and oils used to make soaps?

A
  • natural fats and oils are boiled up with sodium hydroxide which splits fats and oils to prove soap and glycerol
  • this is called saponification
  • fat+sodium hydroxide->soap+glycerol
38
Q

Describe the saturated and unsaturated fats and oils

A
  • saturated oils and fats only have single C-C bonds
  • unsaturated oils and fats have at least one C=C double bond
  • monounsaturated fats contain one C=C double bond
  • polyunsaturated fats contain more than one C=C double bond
39
Q

How can you test for an unsaturated or saturated fat?

A
  • unsaturated fat will decolonize in bromine water, an addition reaction takes place at the double bond and a colourless dibromo compound is formed
  • saturated fats don’t have double bonds so don’t react with bromine so it stays orange
40
Q

How can you harden unsaturated oils?

A
  • by reacting them with hydrogen in the presence of a nickel catalyst at about 60 degrees, this is called hydrogenation
  • the hydrogen reacts with the double-bonded carbons and opens out the double bonds
41
Q

Why are saturated fats worse for you than unsaturated fats?

A

-saturated fats increase the amount of cholesterol in blood which can block up arteries and increase the risk of heart disease

42
Q

How do detergents work?

A
  • they have a hydrophobic and hydrophilic part
  • the hydrophilic end of the molecule forms strong intermolecular forces with water particles
  • the hydrophobic part forms strong intermolecular forces with oil and fats
  • when detergents come into contact with fat or oil a droplet of oil/fat forms surrounded by a coat of detergent
  • this helps lift oily dirt out of fabric
43
Q

How does dry cleaning work?

A
  • there are weak intermolecular forces between solvent molecules and between the molecules of grease
  • when solvent is applied to clothes, intermolecular forces are formed between solvent and grease molecules, so grease is surrounded
  • when solvent is removed the grease is removed with it