QA Test Tomorrow!

there's QA test tomorrow!
grief-

i ate half a new zeland kiwi, and my tongue hurts. >=(

chill-

Qualitative Analysis - Solubility of Salts

[all nitrates and all ammonium, sodium and potassium salts are soluble in water.
most chlorides and sulphates are also soluble,
but the majority of carbonates are insoluble]

but there are exceptions =P


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Muggerinas

prelims are in a few days, do you feel yourself morphing into triple science intense, no life muggerinas? =P

miss begam, if you come here again, help double check my moles explanation! cause im not so sure. =P
our blogs tell about a no life, life; so its not that bad if you ever visit. =P

rin, i hope chemistry is better! =)

and lilin, im trying to grasp the mole concept, at the tip of my fingers.
it's not that hard, don't you worry! =)

yay muggerinas!

chill-

The Mole - What Is It?

here is a mole! =P



Avogadro Number

[A mole is defined as the amount of substance which contains the avogadro number of particles]

and

[The avogadro number is defined as the number of atoms in 12g of the carbon-12 isotope]


[ah, just remember that the avogadro number is 6.02 x 10^23]

=P


Moles Of Atoms

also, the mass of one mole of atoms is its relative atomic mass in grams.
meaning that the relative atomic mass in grams of any element contains the same number of atoms : the avogadro number.

in simpler terms, the number of atoms in 1 mole of any element, is 6.02 x 10^23.



Moles Of Molecules

in the same way,
the mass of one mole of molecules is its relative atomic mass in grams.
meaning that the relative molecular mass in grams of any compound contains the same number of molecules : the avogadro number.

in simpler terms again, this means that
the number of molecules in 1 mole of any compound, is 6.02 x 10^23.


Moles Of Gases

[1 mole of gas at room temperature and pressure (r.t.p)
occupies a volume of 24dm^3 (24000cm^3)]

this is called the molar gas volume as it contains the avogadro number of particles - 6.02 x 10^23.

always quote the temperature and pressure because both affect volume of gas.
the increase of temperature increases the volume,
if pressure increases, volume decreases.

[equal volumes of all gases at same temperature and pressure contain the same number of particles]

and therefore,

[24dm^3 of all gases at same temperature and pressure contain the avogadro number of particles]


for emphasis,



in short,

- a mole is a quantity of substance in grams which contains the avogadro number of particles

- the mass of 1 mole of atoms is its relative atomic mass in grams

- the mass of 1 mole of molecules is its relative molecular mass in grams

- 1 mole of any gas at r.t.p occupies a volume of 24dm^3 (24000cm^3)

- equal volumes of all gases at the same temperature and pressure contain the same number of particles

chill-

Redox Reactions - Summary

Oxidation and Reduction

in short,

REDOX REACTION: when electrons are transfered, and there are changes in oxidation states. both reduction and oxidation occuring at the same time.
such reactions are best expressed in ionic equations.

OXIDATION: the gain of oxygen or the loss of hydrogen.
it also involves the loss of electrons or an increase in oxidation state.

OXIDISING AGENT: a substance which helps oxidation to occur;
like potassium manganate (VII) which helps oxidation by giving oxygen or gaining electrons.

REDUCTION: the loss of oxygen or the gain of hydrogen.
it also involves the gain of electrons or a decrease in oxidation state.

REDUCING AGENT: a substances which helps reduction to occurl
like carbon, hydrogen, carbon monoxide which helps reduction by taking oxygen and giving electrons.

chill-

Redox Reactions - Displacement Reactions

It is best to express redox reactions in terms of ionic equations.
for example,
copper (II) oxide and hydrogen -
the copper (II) ions've gained electrons (been reduced)
and the hydrogen atoms have lost electrons (been oxidised).



another type of redox reactions are Displacement Reactions.

[a displacement reaction is when a more reactive metal displaces a less reactive metal]

this is when the The Reactivity Series comes in handy. =D

for example:

Displacement reactions also occur when more reactive non-metals displace less reactive non-metals.


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Redox Reactions - Reduction and Oxidation at the Same Time

[Substances which help oxidation to take place are called oxidising agents. oxidising agents are reduced in the oxidising process.]

[Substances which help reduction to take place are called reducing agents. redusing agents are oxidised in the reducing process.]


Redox reductions, refined on an electronic basis,
oxidation is associated with a loss of electrons,
while reduction is associated with a gain of electrons

In most oxidation or reduction reactions,
we find that both oxidation and reduction take place at the same time.

pass hydrogen gas over heated copper (II) oxide.


the black copper (II) oxide is reduced to pink copper.
and at the same time, the hydrogen is also oxidised, to form steam.

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Redox Reactions - Oxidation and Reduction, Gain or Loss of Oxygen

[Oxidation is a gain in oxygen, or a loss of hydrogen]

hence, any combustion process is classified as oxidation, as it involves a gain in oxygen.

methane + oxygen -> carbon dioxide + steam
CH4 (g) + 2 O2 (g) -> CO2 (g) + 2 H2O (g)

when methane burns, the carbon atoms in methane gain oxygen and therefore is oxidised.
alternatively, this can be seen as methane losing hydrogen atoms, which is again oxidation.


[Reduction is a loss of oxygen, or a gain in hydrogen]

which is the opposite of oxidation. =P

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Banana Slugs

so MT results are out and LKC says that our batch's not as good this and that and we're the end of cedar this and that.
how encouraging. =(

but i guess everything bad can be pleasant in someway.
maybe LKC cares and she wants us to do well, so she said mean things thinking that it'll drive us to work harder.
it doesnt matter what her true intentions are, its up to us to view situations like this positively.
i know you want your As badly. =P

dont be discouraged if you didnt perform up to expectations!
like uncle bala said, its not the end of the road yet, there's a next chance at the end of the year and i guess we could work harder to make full use of this lovely one-more-chance. =)

chill if you're feeling down, turn that frown around!
things happen that we cannot reverse, the recent results are now a constant.
the next MT exam's a variable and we'll do fine. =D


BANANA! these are for you.
though they're not really chemistry related or chemistry inspiring in any way,
these things are rather cute.

they're called banana slugs.
slimy little garys without shells; i think they really look like goreng pisang. =/



ALL YOURS! =P

chill-

Metals - Displacement Reaction

One application of The Reactivity Series of metals is to be able to predict the displacement power of a metal.
the simple rule that apples is:

[any metal above amother in the reactivity series is capable of displacing it from an aquesous solution of its salt (and its oxide)]

For example, if iron fillings were slowly added, with stirring, to a solution of copper (II) sulphate, its blue colouration would fade and the solution would become light green.


this is because the copper has been 'pushed out' and left as a pink copper metal,
while the iron has 'gone into' the solution as green iron (II) sulphate.

also, in displacement reactions, the powder form is used as it has a greater surface area making reaction faster. =)


in short,

-The Reactivity Series is a list of metals with the most reactive metal on top, and the least reactive below.

-reactive metals form ions easily and react violently with cold water and dilute acids.

-a displacement reaction is when a more reactive metal displaces a less reactive metal from a solution of its salt.
eg. iron fillings displace copper when added to a copper (II) sulphate solution.

chill-

National Day 06

3 days of rest for the schooling part of our nation!
happy red and white day, i hope you had a good one! =P

the tag board tells me miss begam found her way here! cool.
so we all can be very sure she reads our blogs, especially the ones linked from this one. =P

thank you miss begam! but im not as wonderful as you think i am. =P
your sadistic smile displays your joy at having students rack their brains in agony trying to answer your chemistry questions.
but very pretty also la. =P

haha! tomorrow us MT girls get our O level MT results back,
i am genuinely nervous.
somemore later got O level english oral LEH. >=(
why they put everything together!

but anyhow, all the best 4c.
we know we are actually ah, quite smart. =P

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Metals - Properties of Metals and Alloys

over 75% of the elements in the periodic table are metals.
metals are characterised by being shiny, strong solids which are good conductors of head and electicity.
because of such physical properties, they are useful to us. =)

physical metallic properties


however, these properties of a particular metal can be improved if its mixed with another metal.
these mixtures of metals are called alloys.

usually, the atoms of a metal are arranged in regular rows and it is easy for these metal atoms to slide over one another.

sorry for the ugly diagram =P


when metals are mixed together to form alloys,
the alloy is stronger and harder an is less likely do be distorted out of shape when an external pressure is applied.

this diagram is uglier than the previous one =(


metals are made stronger and harder by adding small amounts of another element.

some common alloys


here, are some metals matched with their useful properties and parts played in society.



in short,

-metals are silids with high melting and boiling points.
they are malleable, ductile and
good conductors of heat and electricity.

-Alloys are a mixture of metals, eg. steel bronze, brass

chill-

Random Story and A Picture of Gary

this is a picture of gary.
yingwai and i caught it at the court yard and brought him back to class. he was supposed to be a pet! until he ATE MY HAND WRITTEN GREEN INKED CHEMISTRY NOTES! started ejaculating green stuff, supposedly shit, and looking pale and sick.
so we put him back into the grass. =(



A student asks a teacher,
"What is love?"

The teacher said,
"In order to answer your question, go to the padi field and choose the biggest padi and come back. But the rule is: you can go through them only once and cannot turn back to pick."

The student went to the field, went through first row, saw one big padi,
but he wonders, maybe there is a bigger one later.
Then he saw another bigger one. but maybe there is a even bigger one waiting for him.
Later, when he finished more than half of the padi field,
he starts to realize that the padi is not as big as the previous one he saw,
and he knows he has missed the biggest one, and regrets.
So, he ended up going back to the teacher empty handed.

The teacher told him,
"this is love. you keep looking for a better one, but when it's too late, you realise you have already missed the person."

"What is marriage then?" the student asked.

The teacher said,
"in order to answer your question, go to the corn field and choose the biggest corn and come back. But the rule is: you can go through them only once and cannot turn back to pick."

The student went to the corn field, and this time he is careful not to repeat the previous mistake;
when he reaches the middle of the field,
he picks one medium corn that he feels satisfied with,
and goes back to the teacher.

The teacher told him,
"this time when you were looking for a corn, you looked for one that is just nice,
and you had faith and you believed this is the best one you get.
and this is marriage."

chill-

Methods Of Purification - Testing Purity Of Substances

Melting Point

[a pure substance has a fixed and exact melting point]

the identity of a pure solid can be deduced by its melting point.
the presence of any impurities will lower this melting point.
and if impurities are present, the mixture will melt over a range of temperatures.


Boiling Point

[a pure substance has a fixed and exacty boiling point]

the identity of a pure liquid can be deduced by its boiling point.
the presence of any impurities will raise this boiling point,
and also cause the liquid to boil over a rance of temperatures.


Chromatography

[a pure substance shows only one spot on a chromatogram]

chromatography can not only seperate pigments and dyes,
it can also be used to test for the purity of a substance.

this method is especially useful with complicated chemicals like drugs or food additives which are not easily melted or distilled.

chromatography can be used to identify synthetic dyes in food and check if they are harmful, or pesticide treated vegetables which may be harmful to people.
chromatography can detect chemicals even down to very low concentrations.

chill-

The Unglam

cynnthia says this is boring cause it's all about chemistry, only.
so ah, i shall use a post to impress her with my great photography skills.
good angle, good timing, good eye for impressional shots.

cheep cheep.

=P

chill-

Methods Of Purification - Methods

Dissolving, Fitering and Evaporating

this method is suitable for separating a mixture of solids -
where one must be soluble in the solvent,
and the other insoluble.

consider a mixture of salt and sand.
when water is added to this mixture, only the salt dissolves.

the sand can then be removed by filtration,
as it collects as the residue in the filter funnel.

the salt solution which passes through the funnel is called the filtrate.
this solution can be evaporated to leave behind pure salt crystals.
(the slower the evaporation, the larger the salt crystals.)



Crystallisation

when a solid dissolves in a liquid solvent,
a solution is produced.
when this solution is heated, some of the solvent evaporates.
when the hot solution is allowed to cool, smoe of the dissolved solid reappears as pure crystals.
this process is called crystallisation.

this is useful when impurities are soluble but remain in the solution as it cools.
crystallisation is used to purify sugar and fertillisers like potassium nitrate.

the first crystals formed are always the purest.


Simple Distillation

this is used to separate a pure liquid from a solution.
eg. water from salt water.

the flask is heated and when the solution boils, steam is given off.
this is condensed in a liebig condenser - consisting of a jacket of cold water with the coldest water entering at the bottom and exiting through the top.
the condensed water is called the distillate and this is collected in a receiver.

the thermometer indicates the temperature at which the water vapour distils. it is positioned with its bulb next to the side arm, so that it records the temperature of the steam as it enters the condenser.

in order to maintain even boiling,
'anti-bumping granules' can be added to the salt water.

simple distillation



Fractional Distillation

this technique is used to separate two liquids, said to be miscible liquids, which dissolve in one another.
the separation relies on the difference in boiling points of the two liquids.

eg. ethanol and water.

the fractionating column used is normally packed with glass beads or some other unreactive substance which provides a large surface area for condensation.

when the flask is heated, the vapour produced will contain both ethanol and water. but it will be richer in ethanol as it has a lower boiling point compared to water.

at first, the vapour condenses on the cold fractionating column,
but as the column warms, molecules in the vapour state rise further before condensing.
up the column, the temperature becomes lower.
hence the proportion of the ethanol molecules increases as it has the lower boiling point.

when the temperature of the top column reachers 78 decrees celcius (boiling point of ethanol), the capour of ethanol pass over to the condenser.

when most of the ethanol is boiled off, and the temperature of the top column rises to 100 degrees celius, water passes into the condenser and it would be collected in a different receiver.

fractional distillation



Paper Chromatography

paper chromatography is used to separate colours, pigments, dyes and even colourless substances.

this depends upon the relative solubilites of the solutes in the solvent.

a dye is put in small spots at the bottom of the paper - water loosely combined with the cellulose of the paper.

another solvent is soaked up by the paper and the solutes present in the dye dissolve by different abouts.
some being more soluble in the solvent, moving up the paper;
and some disolving better in the water trapped in the paper hence not travelling far up the paper.

this diffference in solubility allows the different pigments in the dye to be separated.

paper chromatography


in medicine, protiens can be identified using chromatograms.
amino acids present ravel different distances ,like pigments, travel different distances in solvents.
(amino acids are colourless and they are sprayed with a locating agent to make them visible.)

urine can also be analysed by chromatography.


a recap!




sleep well fellow muggers. =P

chill-

Methods Of Purification -Pure Substances and Mixtures

Pure Substances

a pure substance contains only one type of substance,
meaning it only contains one type of atom or molecule.

pure water is a pure substance.
and sea water is a mixture as it is water containing dissolved salt as well as other dissolved substances,
which is referred to as the impurity.


Solids

a pure solid has a fixed and exact melting point.
the presence of an impurity lowers the melting point and that causes the substance to melt over a range of temperature.

eg.
the addition of salt to ice.

pure ice melts at exactly 0 degrees celcius.
when salt is added, it lowers the melting point
to values between -5 to -25 degrees celcius.


Liquids

the presence of any impurity raises the boiling point.

eg.
the addition of salt to water

water boils at 100 degrees celcius.
however, when salt is added, it raises the boiling point.


Mixtures

mixtures are formed by a physical change only.
because of this, they are easy to separate into pure substances.

this process is called purification and this can be achieved by simple physical purification methods like
dissolving, filtering, evaporating, distillation and chromatography.

chill-

A Chemistry Break

wa lao ehhhh!

chill-

i didnt get to take the chem test during the TOP period cause im female and my ovaries hate to cooperate. >=(

oh well. how is chemistry coming along? =P


The universe is one great kindergarten for man.
Everything that exists has brought with it its own peculiar lesson.
The mountain teaches stability and grandeur; the ocean immensity and change.
Forests, lakes, and rivers, clouds and winds, stars and flowers,
stupendous glaciers and crystal snowflakes every form of animate or
inanimate existence, leaves its impress upon the soul of man.
- Orison Swett Marden

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Esters

Manufacture Of Esters

esters are formed by reacting acids with alcohols.

when ethanoic acid is warmed with ethanol,
in the presence of a few drops of concentrated sulphuric acid as a catalyst,
an ester is formed.
this ester is ethyl ethanoate and like all esters, it has a sweet smell.

ethanol + ethanoic acid <-> ethyl ethanoate + water
C2 H5 OH (aq) + CH3 COOH (aq) <-> CH3 COO C2 H5 (aq) + H2O (l)

as this reaction produces an ester,
it is therefore called esterification.
but this reaction is reversible.


Hydrolysis

meaning that the ester obtained can be changed back into an alcohol and organic carboxylic acid by boiling the ester with sodium hydroxide.

this is a reaction with water and it is called hydrolysis.


in short,

-esters are sweet smelling, volatile liquids.

-carboxylic acids react with alcohol to form esters.

-hydrolysis of an ester produces an alcohol and an organic acid.

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Carboxylic Acids

carboxylic acids are weak organic acids containing the COOH functional group and are commonly found in fruits and food stuffs.

The Acid Names, And Its General Formula


*note that methanoic acid's value for n is 0


Uses Of Ethanoic Acid

ethanol + oxygen -> ethanoic acid + water

ethanoic acid cammonly called acetic acid,
is made by the oxidation of ethanol with air.

vinegar is made this way, containing 5% ethanoic acid.
veinegar is used as a food preservative and flavouring.

ethanoic acid is an important industrail chemical;
used with other chemicals in the manufacture of
drugs, dyes, paints, insecticides and plastics.

it is also used to make the organic compound called 'ester',
commonly found in purfume.


Chemical Properties of Organic Acids

it is a weak acid that reacts slowly as
they exists as molecules and
do not form hydrogen ions as easily as mineral acids.

reaction with metals:
they react slowly with metals like magnesium to produce hydrogen gas.

ethanoic acid + magnesium -> magnesium ethanoate + hydrogen

reaction with metal carbonates:
they react slowly with metal carbonates like sodium carbonate to produce carbon dioxide.

sodium carbonate + ethanoic acid -> sodium ethanoate + water + carbon dioxide

reaction with Alkalis:
organic acids also neutralise alkalis like sodium hydroxide to form organic salts and water.

sodium hydroxide + ethanoic acid -> sodium ethanoate + water


in short,

-the general formula for acids is Cn H(2n+1) COOH.

-COOH functional group.

-organic acids are weak acids and they react slowly.

-members of this group have similar properties.


chill-

Alcohols

these compounds contain not only the elements carbon and hydrogen, but also oxygen.

The Alcohol Names, And Its General Formula



Uses Of Ethanol

-alcohol
-good solvent (in purfumes, paints etc.)
-fuel, petrol
-food flavouring


Fermentation (to prepare ethanol)

this process is the conversion of a sugar solution (glucose/sucrose)
into ethanol and carbon dioxide
by the action of yeast.

glucose -yeast-> ethanol + carbon dioxide


Manufature Of Ethanol

it is cheaper to produce alcohol from oil than from sugar.
hence alcohol is produced large scale in the industry from ethene gas.

when steam and ethene are bubbled under high pressure, conversion to ethanol occurs.

this reaction is the addition of water to an unsaturated molecule
seen previously in the alkenes
section under 'addition reactions'.

ethene + water (steam) -> ethanol


Combustion

ethanol + oxygen -> water + carbon dioxide

this reaction is exothermic and produces a lot of heat.
hence ethanol is often used as a fuel.


Oxidation of alcohols

when exposed to air:
ethanol + oxygen -> ethanoic acid + water

ethanol has been oxidised by the air to ethanoic acid,
commonly known as vinegar.


by oxidising agent:
oxidising agents can be used to oxidise ethanol.

when potassium maganate(VII) is warmed with ethanol,
and it turns from pink to colourless;
or when acidified potassium dichromate(VI) turns from
orange to green when warmed with ethanol,

the alcohol has been oxidised.


Covalent Molecule

ethanol is covalently bonded
and thus ions are not present.
the alcohol,
OH group is different from hydroxide ions (OH -).
ethanol is neutral and not an alkali.
it doesn't allow the
passage of electricity
as it is a non-electrolyte.


in short,

-the general formula for alcohols is Cn H(2n+1) OH.

-alcohol's combustion products are CO2 and water

-oxidised by air to form an organic acid and water.

-covalent (neutral and non-electrolyte)

-reacts with organic acids to form esters.


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Alkenes

the family of alkenes are said to be unsaturated hydrocarbons.

The Alkene Names, And Its General Formula.


*no methene available


Preparation

alkene molecules can be prepared by cracking alkanes.
hydrogen is formed as a result of the cracking process.
alternatively, medium-sized alkanes undergo cracking
to form smaller, more useful
alkanes (octane for petrol)
and alkenes (ethene)
which can be used to form plastics like polyethene.
(for a diagram, refer to page 272 of our comprehensive chemistry text book.)


Combustion

alkene + oxygen -> water + carbon dioxide


Addition Reaction

*characteristic reaction of unsaturated compounds
*addition reaction is fater than substitution reactions


hydrogenation:
alkene + hydrogen -> alkane

bromination:
bromine decolourises from brown to colourless when reacted with alkenes.
hence the bromine test is used to distingush alkenes from alkanes.

hydration:
alkene + water -> alcohol

polymerisation:
alkenes can join together to form giant molecules called polymers.
*polymer = thousands of identical units called monomers joined together.

eg. the polymer - polyethene, is made up of many ethene monomer molecules.
(this will be further explained in the unit macromolecules. yuck. =P)


in short,

-the general formula for alkenes is Cn H2n.

-alkenes are often formed by cracking alkanes.

-combustion products are CO2 and water.

-alkenes undergo addtion reactions as they are unsaturated molecules because they contain double carbon-carbon covalent bonds.

-alkenes can undergo polymerisation.


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Alkanes

alkanes are said to be saturated hydrocarbons.

The Alkane Names, And Its General Formula.


*difference between each successive member of alkane is CH2.


Boiling Points

there is a gradual increase in boiling point as the molecule becomes larger.
the first 4 series are gases, with their boiling points below room temperature.
for an alkane to be a waxy solid, it needs to have a melting point above room temperature.


-combustion

complete combustion-
alkane + oxygen -> carbon dioxide + water

incomplete combustion-
propane + oxygen -> carbon monoxide + water


-substituion with Cl

alkane + chlorine -> chloroalkane + hydrogen chloride


in short,

-the general formula for alkanes is Cn H2n+2

-alkanes are saturated compounds as they contain only single carbon-carbon covalent bonds.

-the boiling points gradually increase down the series.

-combustion products are CO2 and water.

-alkanes undergo substitution reactions as they are saturated molecules.


chill-