Friday, 24 August 2012

The Reactions to Know

These are the equations you need in your toolbox to support your answers in the HSC. Some are handy to push for the high marks in extended response questions. Some are VITAL to know (eg 3, 4, 7, 8, 10, 11, 12, 14, 17, 18, 19) to achieve the basics of the course.

If you are having trouble remembering them – try to think of them in context. Eg remember what happened in your fermentation experiment, remember how we decarbonated soft drink, remember how ozone blocks UV rays and why CFC’s decompose ozone etc
 
Click on the images for a larger version.

1) Addition polymerisation  eg PVC
HINT
Show 2n monomers so you can show the repeating structure of the polymer chain. NB the square brackets to signify the repeating unit

2) Polymerisation of glucose to form cellulose
HINTS

1)      If you need help remembering the structure of glucose – let me know – I’ve taken a few people through it and it is (for the most part) working

2)      Every second glucose is inverted.

3)      Being a condensation polymerisation there is a water molecule produced for each link – there is always one less link than monomers (think about why) thus there is always one less water molecule than monomers.

4)      Showing four glucose monomers is ideal to illustrate the above but under time pressure two would suffice as long as you note that every second one is inverted.


3) Addition of bromine water to cyclohexene
HINTS

1)      use the carbon chemistry shorthand – ie don’t bother drawing the C and H atoms

2)      Bromine water is an aqueous solution, but cyclohexene and 1,2-dibromocyclohexane are non-soluble in water so are liquids.

4) Fermentation
HINTS

1)      you *SHOULD*  know that ethanol and carbon dioxide are products, that the glucose needs to be aqueous and yeast is required. We do the experiments (and you learned all about ethanol production) so you don’t need to think about these things – you should just remember.

2)      If you know the products then it is just a simple case of remembering that there are TWO of each product.

3)      This is one of the only reactions involving carbon compounds where you don’t need to use structural equations

 
5) Combustion of an alkanol  eg ethanol
HINTS

1)      For all hydrocarbon combustions – balance carbon, then hydrogen, then oxygen (CHO)

2)      Remember that there is an oxygen in the alkanol so you need one less oxygen than normal (ie one of the reasons why ethanol has such complete combustion)

 
6) Incomplete combustion  eg ethanol
HINTS

1)      The simplest incomplete combustion is where C(s) is the only product

2)      Use CHO

 
7) Dry cell reactions
HINTS

1)      Never hate mangoes watery monkey nuts

2)      You should know that ammonium has a charge of +1 (it is the ‘t’ in hate)

 
8) Silver cell reactions
HINTS

1)      The silver and zinc reactions are basically opposites of each other

2)      The oxide and hydroxide must be on opposite sides of the equations

3)      Hydroxide is consumed at the anode and produced at the cathode

 
9) Radioactive decay
HINTS

1)      RULE 1 – If Z > 82 = alpha emitter

2)      RULE 2 – If n/p is too high = beta emitter

            Z < 20 : n/p = 1:1

            Z ~ 50 : n/p = 1.3:1

Z ~ 80 : n/p = 1.5:1

Eg 1) C-14

C has 6 protons

Thus there are 14-6 = 8 neutrons

n/p = 1.33:1 – too high s it should be 1:1 – thus it is a beta emitter

Eg 2) Hg-210

Hg has 80 protons

Thus there are 210-80 = 130 neutrons

n/p = 1.625:1 – too high should be 1.5:1 – thus it is a beta emitter

Eg 3) Sn-115

Sn has 50 protons

Thus there are 115-50 = 65 neutrons

n/p = 1.3:1 – just right = stable

Eg 4) At-217

At has 85 protons – thus it is an alpha emitter

 

10) Acid rain
HINT

All you have to show is that it forms an acid – thus if you can show sulphur dioxide forming sulfurous acid or nitrogen dioxide forming its mixture of nitric and nitrous acid you can stop

11) CO2 solubility
HINTS

1)      Generally, non-polar covalent molecular compounds do not dissolve in water. Carbon dioxide is an exception because it REACTS with water

2)      The reaction is as simple as just adding the atoms of carbon dioxide and water together – remembering to use an equilibrium sign!

 
12) Citric acid
HINTS

1)      Remember that it is the oxygen of the hydroxyl group that bonds to the carbon

2)      Carboxylic acid groups have a double bonded oxygen and a hydroxyl group

 
13) Esterification  eg pentyl ethanoate
HINTS

1)      Remember it is EQUILIBRIUM

2)      Remember that it needs a concentrated sulfuric acid catalyst

3)      Remember that is produces water

4)      Remember that primary alkanols from propanol onward need to end with ‘…an-1-ol’

 
14) Haber equilibrium
HINTS

1)      Know the formula of ammonia

2)      Know that it comes from hydrogen and nitrogen gas

3)      Balance the equation

4)      Know that it is in equilibrium

15) Ozone
HINTS

1)      When writing the ozone equilibrium always show O3 absorbing UV – this is so you can explain how the ozone layer absorbs UV

2)      It is good practise to label the coordinate covalent bond for ozone (distinguishing the electrons from each oxygen is also useful)

 
16) CFC’s decomposing ozone
HINT – to show that it is a catalyst for ozone decomposition you must show them reforming (ie catalysts provide a reaction pathway that lower the activation energy but are not consumed in the reaction).

 
17) Rusting
HINT – if you want to do well in the shipwrecks option you need to know these four equations. They can be used to explain just about everything about the factors that effect rusting and rust protection systems

 
18) Sulfate reducing bacteria
HINT – Soloh ate his two sneakers for water. Need I say more?

 
19) Precipitation
HINTS – This is as simple as I can make the solubility rules for the HSC

1)      All Group 1 metal, ammonium, nitrate, acetate (and phosphate in acidic conditions) compounds are SOLUBLE

2)      All other carbonates and phosphates are INSOLUBLE

3)      Chlorides are soluble except lead and silver

4)      Hydroxides are soluble except lead, silver, iron and copper

5)      Sulfates are soluble except for lead, silver, barium and calcium

6)      Carbonates bubble in acid

7)      Flame tests – barium = apple green, calcium = brick red, copper = emerald green

 

 

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