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Sunday, October 5, 2008

title:{Chemistry-(2)}

Chemistry pt.2

Indicators
-Litmus Paper
-Universal Indicator
-Phenolphthalene
-Screened methyl orange
-Methyl orange
-pH meter

Salts
-Ionic compounds
-Acids--->Salt
HCl--->ZnCl, NH4Cl, NaCl, FeCl2
HNO3--->Zn(NO3)2, NH4NO3
H2SO4--->ZnSO4,(NH4)2SO4
-Normal salts: NaCl, Na3PO4
-Acid salts: Na2HPO4, NaH2PO4
-Crystallisation, eg. CuSO4 + 5H2O
+Purification
+Crystalline form(blue)
+Anhydrous form(white)
-Methods of preparing salts
1. Acid + insoluble metal/base/carbonate
2. Titration-->using an indicator to determine end-point, evaporation/crystallisation to get salt
3.Precipitation-->mix 2 aqueous solutions, precipitation forms, filter off residue(salt), rinse with distilled water, dry between filter paper.

Moles
Moles=given mass ÷ molar mass
=no. of particles ÷ (6 x 10E23)
=concentration of solution x volume of solution(mv)
=given volume ÷ molar volume(24cm³ at r.t.p.)
Composition(eg. % of a in b)=molar mass of a ÷ molar mass of b x 100%
Stoichiometry-->calculation involving equation(balanced equation)
*eg. pAB + qCD --->...
no. of moles of AB p m1v1
--------------------- = --- = --------
no. of moles of CD q m2v2
Percentage yield=experimental yield ÷ theoretical yield x 100%
Percentage purity of a substance=mass of pure substance ÷ mass of impure substance x 100%

Metals
Reactivity series(Going down, less reactive)
K(reacts with cold water, alkali metal) 2K + 2H2O(l)--->2KOH(aq) + H2
Na(reacts with cold water, alkali metal) 2Na + 2H2O(l)--->2NaOH(aq) + H2
Ca(reacts with cold water) Ca + 2H2O(l)--->Ca(OH)2(aq) + H2
Mg(reacts with steam) Mg + 2H2O(g)--->MgO(s) + H2
Al(reacts with steam)
Zn(reacts with steam)
Fe(reacts with steam) 3Fe + 4H2O(g)--->Fe3O4(s) + 4H2
Pb(no reaction)
H
Cu(no reacts with steam)
Ag(no reacts with steam)
Au(no reacts with steam)
Metals in HCl
-Potassium/sodium--->Explosive reaction
-Calcium--->Vigorous reaction
-Magnesium--->Rapid reaction
-Zinc--->Moderately fast reaction
-Iron--->Slow reaction
-Copper/lead/silver--->No reaction
Colour of metal
Fe2+ ---> green
Fe3+ ---> yellow
Cu2+ ---> blue/green
Zn2+, Mg2+, Pb2+, Na2+, ... ---> colourless
KMnO7 ---> Purple
K2Cr2O7 ---> orange
*The more reactive the metal, the more readily it forms +ve ions(loses electrons).
Therefore the more stable the compound formed. Stable compounds will not be easily decomposed by heat.*
Blast Furnace
Iron is extracted by reduction using carbon.
C + O2--->CO2
CO2 + C--->2CO
3CO + Fe2O3--->2Fe + 3CO2
To remove impuries(SiO2->sand)
CaCO3--->CaO + CO2
SiO2 + CaO--->CaSiO3(l) ->Calcium silicate(slag)
Add Haematite, Coke or limestone into blast furnance to remove impurity.
*below slag in blast furnace is molten/pig iron*
Uses of metals(Iron & Steel)
Iron frm cast iron mostly goes to making steel.
Steel is an alloy made up of carbon & other materials.
High carbon steel->Stainless Steel
Conditions for rusting
1. Air(O2)
2. Water
Example: Hydrated iron(III)oxide->Fe2)3 x H2O
Methods to prevent rusting
1. Painting->easy to apply but too thick, difficult to maintain
2. Apply Oil->easy to apply but will result in oily surface
3. Plastic coating->effective
4. Electroplating-> thin but expensive
5. Galvanizing/Sacrificial protection->covering metal with other more reactive metals
Mild Steel
-Less carbon content
-car body, machinary
-strong, hard & malleable
High carbon steel
-More carbon content
-boring tools, hammers, knifes
-harder but brittle

Periodic table
Atomic radius increases across a period, down a group.
Gp I - Alkali metals
-down the group, decrease in m.p., b.p. & increase in reactivity
Gp VII - Halogens
down the group,
-increase in m.p., b.p.
-decrease in reactivity
-size of atom increases
-attractive force of valence electrons decrease
-colour intensity increases

Atoms
Sub-atomic particles
-Electrons(-ve charge)
-Protons(+ve charge)
-Neutron(no charge)
Isotopes
-same no. of proton, different no.s of neutron

Others
Acids turn blue litmus paper red.
Soil pH is important as it affects plant growth.
Sulphur dioxide as a bleaching agent(removes oxygen from dyes), as a preservative(prevents growth of mould & bacteria), but it is poisonous.
Sulphuric acid used in manufacture of fertillisers, manufacture of detergents & as battery acid in cars.

Oxidation & reduction
Oxidation
-Gain of oxygen
-Loss of hydrogen
-Loss of electrons
-Gain in oxidation state
Reduction
-Loss of oxygen
-Gain of hydrogen
-Gain of electrons
-Decrease in oxidation state
Redox reaction
-When both oxidation & reduction happen together
Oxidising agents
-Bromine
-Chlorine
-Concentrated sulphuric acid
-Nitric acid
-Oxygen
-Potassium Manganate(VII)
-Potassium Dichromate(VI)
-Hydrogen Peroxide
Reducing agents
-Carbon
-Carbon monoxide
-Hydrogen
-Hydrogen sulphide
-Metals
-Potassium iodide
-Sulphur dioxide
-Ammonia

All rite, guess tt's the end... Phew! Took a long time revising Chem! Anyway, the reason why I took sooo long is because I was playing the com, hahaXDXD Yup, tts all, bb!

A lollipop a day, keeps my sorrows away...

11:03 AM;