Lesson Notes- Grade 8

mole concept

acids and bases

chemistry Revision Notes

Titration

Titration is an important topic in O/L chemistry cox it has been appearing in P4 papers for many yrs as a compulsory question. So its important that u ans the questions well to obtain maximum marks from it. There has been a similar pattern of how the question appears. so let me try to summarise hopin dat it can help u..well da common steps include;-
1. finding da mass of da sample ; just substract da given values.
2. apparatus dat cud be used to transfer 25cm3 of solution to da conical flask: pipette ;check ur spelling once again!
3. indicTOR colour change; well here check which is there in da burette? if it contains acid final indicator colour for methyl orange wl b orange or red..so jus write yellow to orange/red

well i wl try to write the remaining in some other time...
any questions??? let me know.

Titration notes just click the link Titration

chemistry of love..

While talkin abt relationships i often hear ppl usin phrases like 'they ve gud chemistry', 'there is a chemistry goin on betwyn da 2''...nd so on..well it cud b true,cox there r chemicals that r involved in attractin 1 to another.

one such chemical is phenylethylamine.it is a natural compound biosynthesized from the amino acid phenylalanine by enzymatic decarboxylation. in da human brain it is believed to function as a neurotransmitter. simple actions such as meetin da eyes, touchin da hand can trigger the release of dis chemical frm da brain resultin sweaty palms, general restlessness etc as common symptoms of love..

phenylethylamine is an aromatic amine nd is a colourless liquid at room temperature.it is also water soluble.

A very interesting thing is that chocolate is known to have very high level of this chemical…perhaps that’s the reason y it is considered as a perfect gift for ur gf/bf..

phenylethylamine is therefore known as da luv molecule..

which type of cooking oil better??

While choosing cooking oil and other types of fats, try to select one that is healthier compared to the other.

Fats can be classified as saturated (contains C-C single bonds) and unsaturated (at least a C=C double bond) fats which include both monounsaturated and polyunsaturated fats.

Consumption of small amount of saturated fats is essential although excessive amounts can lead to coronary heart diseases. Since saturated fats as well as trans fats can increases LDL cholesterol (bad cholesterol) in our body. Monounsaturated fats and polyunsaturated fats appear to not raise LDL cholesterol; some studies suggest they might even help lower LDL cholesterol slightly when eaten as part of a low-saturated and trans-fat diet.

So before choosing a bottle of cooking oil check the label. Always go for the one that contains mostly polyunsaturated or monounsaturated one. Sometimes you may find Omega-3, well that’s a good one select it.

Canola oil, Sesame oil, safflower oil, Sunflower oil are among good ones which contains mostly unsaturated fats compared to saturated fats.

Palm oil, coconut oil isn’t good cox mostly its saturated fats.

Another important fat is margarine which is made by the hydrogenation of vegetable oils using a nickel catalyst. Addition of hydrogen will result in transforming the oil into a saturated fat and increases melting point so becomes a solid and is spreadable. But this isn’t good for your health. So that’s why nowadays partial hydrogenation is done so some amount of unsaturation. This is known as soft margarine so aware of it as well.

The next question is butter or margarine which is better? Butter contains saturated fats and cholesterol, both can increases the bad cholesterol LDL. Soft margarine, the recent one contains unsaturation so can say its better than butter.

So know about your fats, and chemistry is there to make a difference…

Nanotubes nd Buckyballs

carbon nanotubes are allotropes of carbon. it is one form of carbon jus like dat of graphite and diamond.its a very recent tecnology nd its invention is da direct result of the synthesis of buckminsterfullerene, C₆₀ , and other fullerenes, in 1985. The discovery that carbon could form stable, ordered structures other than graphite and diamond stimulated researchers worldwide to search for other new forms of carbon nd dis leads to nanotube discovery in 1991.

Carbon nanotubes are molecular-scale tubes of graphitic carbon with outstanding properties. They are among the stiffest and strongest fibres known, and have remarkable electronic properties ie it can conduct electricity better than dat of copper wires and many other unique characteristics. For these reasons they have attracted huge academic and industrial interest.even in da last oct/nov. O/L chemistry paper there was a question based on it as well.

cake chemistry

Do u knw behind ny gud cake is gud chemistry.
The essential ingredients to make a cake include flour,baking powder which is mainly sodium bicarbonate with acidifying agent (cream of tartar), and also a drying agent (usually starch); salt(Sodium chloride); sugar, eggs etc.
• The role of baking powder is to enlarge the bubbles in the fat, causing the cake to rise to its potential.
• Fats tenderize the cake, softening and moderating the structure, and enhance flavor.
• Sugar tenderizes and moistens a cake.
After mixing da ingredients in a proper way,then the next step is baking. In the early part of baking there is some decrease in batter viscosity. The fat begins to melt and the air cells form. da air cells then allow the accumulation of gases and water vapour generated by heat. da produced water vapour and da CO2 leads da expansion of da batter.

so chemistry nd cookin share a lot in common right!

Death of 5 young men at the Male' Fish Market well: What could be the chemistry behind it?

Last night five men died in Male in an incident that occurred at Male Fish Market. According to reports the five men suffocated and died in a deep well, where they went down to do some drilling work. Many suspects the death was due to the inhalation of poisonous or toxic gases. Methane is a gas that could be present in such a well. It is a colourless, odourless gas and is lighter than air. Methane is not considered toxic, but it is an asphyxiant at a concentration of over 50 per cent in air. In other words,it can displace oxygen in confined spaces and could result in suffocation. Therefore methane gas in a enclosed space is considered to be a safety hazard.
CH4 +O2 =>CO2 + H2O

Methane is not the only gas that could be present in such a closed well. Gases such as carbon dioxide(from respiration and microbial activity),hydrogen sulphide H2S(formed from bio-chemical reduction reaction of naturally occurring sulfate ions in water or from the decomposition of organic matter that contains sulfur under anaerobic condition)maybe also be present.Hydrogen sulfide has been reported in many countries as the leading cause of sudden death in work place. At concentrations in air of approximately 300 ppm, H₂S can be immediately deadly.

Electroplating

* Electroplating involves the coating of an electrically conductive object with a layer of metal using electrolysis.
* Electroplating is commonly carried out to:
· Enhance a metal’s appearance
· Prevent corrosion of the metal
* For electroplating, the electrolysis cell is adapted from the type normally used. The anode is not made from inert graphite or platinum, but from the metal present in the electrolyte solution. In these cases the anode slowly dissolves in the solution as the current is passed.


At the positive (+) anode, the process is an oxidation, electron loss, as the metal atoms dissolve to form metal(II) ions.
M(s) ==> M2+(aq) + 2e-
at the negative (-) cathode, the process is a reduction, two electron gain by the attracted metal(II) ions to form neutral metal atoms on the surface of the metal being coated.
M2+(aq) + 2e- ==> M(s)
For silver plating it is Ag+, Ag and a single electron change.
Any conducting (usually metal) object can be electroplated with copper or silver or steel with zinc or chromium as anti-corrosion protective layer.

Uses of electroplating:
* Tin-plating steel cans to prevent them from rusting.
* Chromium- plating articles such as car bumpers, kettles, bath taps etc.Silver-plating.

Fuel Cell

Fuel cells are 'battery systems' in which two reactants can be continuously fed in. The consequent redox chemistry produces a working current.
Hydrogen's potential use in fuel and energy applications includes powering vehicles, running turbines or fuel cells to produce electricity, and generating heat and electricity for buildings and very convenient for remote and compact situations like the space shuttle.
When hydrogen is the fuel, the product of its oxidation is water, so this is potentially a clean non-polluting and non-greenhouse gas? fuel.
Most fuel cells use hydrogen, but alcohols and hydrocarbons can be used.
A fuel cell works like a battery but does not run down or need recharging as long as the 'fuel' supply is there.
A fuel cell consists of two electrodes consisting of a negative electrode (or anode) and a positive electrode (or cathode) which are sandwiched around an electrolyte (conducting salt/acid/alkali solution of free ions).
Hydrogen is fed to the (-) anode, and oxygen is fed to the (+) cathode.
The platinum catalyst activates the hydrogen atoms/molecules to separate into protons (H+) and electrons (e-), which take different paths to the (+) cathode.
The electrons go through an external circuit, creating a flow of electricity.The protons migrate through the electrolyte and pass through the semi-permeable membrane to the cathode, where they reunite with oxygen and the electrons to produce water.

The hydrogen-oxygen cell with an alkaline electrolyte is known as the 'alkali fuel cell' and is used in NASA's space shuttle craft.
anode reaction (i) 2H2(g) + 4OH-(aq) ==> 4H2O(l) + 4e-
cathode reaction (ii) O2(g) + 4H+(aq) + 4e- ==> 2H2O(l)
overall cell reaction: 2H2(g) + O2(g) ==> 2H2O(l)
The electrolyte is the alkali potassium hydroxide solution, KOH(aq).
In both acid or alkaline hydrogen-oxygen fuel cells the oxidation state changes are
(i) oxidation H(0) ==> H(+1), (ii) reduction O(0) ==> O(-2)

In the last oct/Nov paper,there was a question based on hydrogen-oxygen fuel cell.
anode equation: H2(g) + 2OH-(aq) = 2H2O(l) + 2e-

question is
(i) what type of reaction is this? Explain your answer. [2]
so in your answer mention it as an oxidation reaction. since electrons are being lost.

(ii) at the cathode oxygen reacts with water to form hydroxide ions. write an ionic equation for this reaction.

ans: 2H2O(l) + O2(g) + 4e- = 4OH-(aq)

in an ionic equation you need to write the state symbol,the equation also need to be balanced.
you can start balancing the charges first so that there will not be any difficulty.

Molten Electrolytes vs Aqueous Electrolytes

Electrolysis is all abt breaking down of an electrolyte into its constituent elements.The products discharged at electrodes depends on da type of electrolyte used in da process, molten or an aq. electrolyte.
if it is a molten one dan its easy to knw da products dat wl b formed. metal ion wl becom a metal nd da non-metal ion to anon-metal...

Electrolysis

Electrolysis is an important O/L chem topic based on its weightage and time spent to teach the topic. On the other hand many students find difficult to answer electrolysis questions. Basic chemistry is essential prerequisite to understand the concepts. For example chemical formula,symbols, state symbols etc.

Learning objectives under dis topic includes:

(a) *describe electrolysis as the conduction of electricity by an ionic compound (an
electrolyte), when molten or dissolved in water, leading to the decomposition of the
electrolyte
(b) *describe electrolysis as evidence for the existence of ions which are held in a lattice
when solid but which are free to move when molten or in solution
(c) describe, in terms of the mobility of ions present and the electrode products, the
electrolysis of molten lead bromide, using inert electrodes
(d) predict the likely products of the electrolysis of a molten binary compound
(e) apply the idea of selective discharge (linked to the reactivity series for cations, see
9.2) to deduce the electrolysis of concentrated aqueous sodium chloride, aqueous
copper(II) sulphate and dilute sulphuric acid using inert electrodes
(f) predict the likely products of the electrolysis of an aqueous electrolyte, given relevant
information
(g) construct ionic equations for the reactions occurring at the electrodes during the
electrolysis of the substances mentioned in the syllabus