Chemistry Form 4 - Chapter 7: Examples of Acid - Base Indicator

Acid - base indicator is used in titration method to determine the end point of neutralisation process. The acid-base indicator basically is some weak organic acid or base dye that changes colours at definite pH values.

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Chemistry Form 4: Chapter 2 - Atomic Symbol, Proton Number and Nucleon Number

Atomic Number = Proton Number

Mass Number = Nucleon Number

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Chemistry Form 4: Chapter 2 - Electron Arrangement of Atom

Electrons are arranged in shells at different distances around the nucleus. As we move across each row of the Periodic Table the proton number increases by one for each element. This means the number of electrons also increases by one for each element.

Starting from the simplest element, hydrogen, and moving through the elements in order we can see how the electrons fill the shells. The the innermost shell (or lowest energy level) of electrons is filled first. This shell can contain a maximum of two electrons.

Next, the second shell fills with electrons. This can hold a maximum of eight electrons. When this is filled, electrons go into the third shell, which also holds a maximum of eight electrons. Then the fourth shell begins to fill.

Electron arrangement for the first 20 elements in the Periodic Table

 Number of valence electrons influences the chemical properties of element by losing electron to form ionic bond or gaining electron to form covalent bond in order to attain noble gases electron arrangement. Thus, all elements having the same valence electrons will show the same chemical properties.

Chemistry Form 4: Chapter 4 - Dmitri Mendeleev ( Father of Periodic Table)

Dmitri Mendeleev was born at Tobolsk, Siberia in 1834 and died in 1907. Mendeleev studied science at St. Petersburg and graduated in 1856. In 1863 Mendeleev was appointed to a professorship and in 1866 he succeeded to the Chair in the University. 

Mendeleev is best known for his work on the periodic table; arranging the 63 known elements into a Periodic Table based on atomic mass, which he published in Principles of Chemistry in 1869. 

His first Periodic Table was compiled on the basis of arranging the elements in ascending order of atomic weight and grouping them by similarity of properties. 

Mendeleev provided for variance from strict atomic weight order, left space for new elements, and predicted three yet-to-be-discovered elements including eke-silicon and eke-boron. His table did not include any of the Noble Gases, however, which had not yet been discovered.

The original table has been modified and corrected several times, notably by Moseley, but it had accommodated the discovery of isotopes, rare gases, etc.

Chemistry Form 4: Chapter 2 - Structure of an Atom

   

• Atom consists of electrons surrounding a nucleus that contains protons and neutrons.
• Electrons are arranged around the nucleus in energy levels or shells. 
• The mass of an atom is concentrated in nucleus which contained the protons and neutrons.
• The nucleus is positively charged because of the presence of protons which are positively charged and the neutrons are neutral.
• The atom is neutral because the number of protons and the number of electrons are equal

Subatomic particles	Symbol	Relative mass	Relative   charged	Position
Proton	P	1	+1	Nucleus
Neutron	N	1	0
Electron	e-	1/1837 » 0	-1	Orbit

Symbol of Element

Chemistry Form 5: Chapter 5 - Making of Soap

Soaps are sodium or potassium salts of fatty acids. Soaps are prepared by hydrolyzing fats or oils under alkaline condition. This reaction is called saponification.

·         The fats or oils are hydrolysed first to form glycerol and fatty acids. The acids then react with an alkali to form the corresponding sodium or potassium salts.

·         The soap formed can be precipitated by adding sodium chloride. This is because sodium chloride lowers the solubility of soap in water.

·         The glycerol and excess sodium hydroxide solution are removed by rinsing the soap formed with water.

·         Soaps feel slippery and form lather when they are shaken with water.

Chemistry Form 4: Chapter 2 - Bohr's Atomic Model

Neils Bohr was born on October 7, 1885 in Copenhagen, Denmark. In 1922 he won the Nobel  prize for physics. Bohr was a professor at the unoversity of Copenhagen. Neils Bohr produced a theory about the structure of an atom based on Rutheford's Plum Pudding model. Bohr discovered that the electrons travel in orbits. Outer orbits could hold more electrons than the inner orbits. He suggested that when an electron jumps from an outer orbit to an inner orbit it emits light which called photon.

This model was created by Neils Bohr in 1915. In the center is the nucleus which is composed of protons and neutrons. It is orbited by electrons. The nucleus is about 100,000 times smaller than the radius of the atom.

Chemistry Form 5: Chapter 1 - Effect of Concentration on Rate of Reaction

Experiment to show the effect of concentration on reaction rate

Sodium thiosulphate solution react with dilute sulphuric acid to form a yellow precipitate of sulphur. In this experiment, the time taken for the formation of sulphur to cover the mark 'X' until it disappears from sight can be used to measure rate of reaction.

As the concentration of sulphuric acid is increased, the rate of reaction between sulphuric acid and sodium thiosulphate increases.

Explanation using collision theory

·      When the concentration of the solution of a reactant increases, the number of particles per unit volume of the solution also increases.

·      With more particles per unit volume of the solution of the reactant, the frequency of collision increases.

·      This causes the frequency of effective collision to increase. Hence, the rate of reaction increases.

Chemistry Form 4: Chapter 2 - Rutherford Atomic Model

The Gold Foil Experiment

Rutherford bombarded a very thin leaf of element gold with a stream of high speed positively charged particles. These positively charged particles are alpha radiation from helium nuclei. 

As expected, most alpha particles went right through the gold foil but to his amazement, a few alpha particles rebounded almost directly backwards due to same positive charge repulsion force.

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This proved that:

1. the atom had a dense but very small positive nucleus
2. the electrons were far away from the nucleus
3. the electrons were separated from the nucleus by a lot of empty space

Chemistry Form 5: Chapter 2 - Dehydration of Alcohol

ALCOHOL -------> ALKENE

• In the dehydration of alcohols, a molecule of water is eliminated from each alcohol molecule to produce alkene.
• There are two methods of dehydration:

a)      Ethanol vapour is passed over a heated unglazed porcelain chips, porous pot, pumice stone or alumina (aluminium oxide).

b)      Ethanol is heated under reflux at 170 °C with excess concentrated sulphuric acid.

 

School Laboratory Experiment

• Alkene can be tested by decolourising brown bromine water or decolourising purple acidified potassium manganate (VII) solution.

Chemistry Form 4: Chapter 9 - Making of Alloy

An alloy is a mixture of two or more elements with a certain fixed composition in which metal is the major component.

The making of alloy is:

• To increase the strength and hardness of a pure metal.
• To prevent corrosion.
• To improve the appearance of a pure metal.

Pure Metal

·     Pure metal is made up of one type of atoms that are in same size. Therefore, when a force is applied, the layers of atoms can slide over one another. Thus, metals are ductile or can be stretched. ·     There are some empty spaces in between the pure metal atoms. When a metal is knocked or pressed, groups of atoms may slide and then settle into new positions. Thus, metals are malleable or can be shaped.

Alloy

·     Some of the spaces between the metal atoms are filled up by the foreign atoms which may be bigger or smaller than the original metal atoms. ·     The presence of foreign atoms disrupts the orderly arrangement or the pure metal. ·     The layers of metal atoms are prevented from sliding over one another easily. This makes alloys stronger and harder than pure metals.

Examples of alloy

Alloy	Composition
Steel	99 %   iron     +   1 %  carbon
Stainless steel	74 %   iron  +  18 % chromium  + 8 % nickel
Bronze	90 %   copper   +   10 %  tin
Brass	70 %  copper   +   30 %   zinc
Magnalium	70 %  aluminium   +   30 %   magnesium
Duralumin	95 %  aluminium   +  4 %  copper    +  1 %   magnesium
Pewter	97 %  tin   +    3 %  lead and antimony
Solder	50 %   tin   +    50 %  lead
cupronickel	25 %  copper    +    75 %  nickel

Chemistry Form 5: Chapter 2 - Hydrogenation

Hydrogenation process is addition reaction to convert alkene becomes alkane. It converts unsaturated compound to saturated compound.

Ethene reacts with H₂ at 180 °C in the presence of nickel or platinum catalyst to produce ethane

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Application of hydrogenation: Making Margarine

Vegetable oils often contain high proportions of polyunsaturated and mono-unsaturated fats (oils), and as a result are liquids at room temperature. That makes them messy to spread on your bread or toast, and inconvenient for some baking purposes.

You can "harden" (raise the melting point of) the oil by hydrogenating it in the presence of a nickel catalyst. Conditions (like the precise temperature, or the length of time the hydrogen is passed through the oil) are carefully controlled so that some, but not necessarily all, of the carbon-carbon double bonds are hydrogenated. This produces a "partially hydrogenated oil" or "partially hydrogenated fat".

Chemistry Form 4: Chapter 9 - Haber Process

1. The physical properties of ammonia are:
• Colourless and alkaline gas
• Strong pungent smell
• Highly soluble in water

2. Ammonia usually produces white fumes of ammonium chloride when reacted with hydrogen chloride.

3. The main uses of ammonia are:
• Manufacturing nitrogen fertilizers
• Manufacturing nitric acid through Ostwald process.
• To make explosives, dyes, household cleaners and nylon
• As a cooling agent.

Making of Ammonia

Ammonia is manufactured by combining nitrogen and hydrogen in an important industrial process called the Haber process. The reaction is reversible and the production of ammonia is exothermic.

• Nitrogen gas is obtained from the fractional distillation of liquid air.
• Hydrogen gas is obtained through the reaction between natural gas and steam.
• Nitrogen and hydrogen are mixed in the ratio of 1 : 3

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How to separate ammonia

When the gases leave the reactor they are hot and at a very high pressure. Ammonia is easily liquefied under pressure as long as it isn't too hot, and so the temperature of the mixture is lowered enough for the ammonia to turn to a liquid. The nitrogen and hydrogen remain as gases even under these high pressures, and can be recycled.

 An ammonia production plant. Photo courtesy of WMC Resources Ltd

 

Chemistry Form 5: Chapter 4 - Exothermic and Endothermic Reaction

Chemical energy is needed to transform a chemical substance into a new product through chemical reaction. Therefore, breaking or formation of chemical bond involves energy, which may be either absorbed or released from a chemical reaction.

• To break the chemical bond, energy from surrounding is absorbed resulting decrease of temperature of surrounding.
• To form the chemical bond, energy from reaction is released to the surrounding resulting increase of temperature of surrounding.

 

Exothermic Reaction	Endothermic Reaction
Chemical reaction that gives out heat to the surroundings.	Chemical reaction that absorbs heat from the surroundings.
Temperature of the surroundings increases.	Temperature of the surroundings decreases.
The total energy of reactants is more than total the energy of products.	The total energy of reactants is less than the total energy of products.
Bond formation releases more energy than is required in the bond breaking.	Bond breaking requires more energy than the energy that is released during bond formation
Examples: Combustion of fuel, burning of metal, neutralization, respiration, rusting of iron, reaction of a reactive metal with acid, reaction of alkaline metals with water, Haber process, freezing, condensation, dissolving alkali or concentrated acid in water, dissolving anhydrous salts in water.	Examples: Thermal decomposition of nitrate or carbonate salts, reaction of acid with hydrogen carbonate, photosynthesis, melting, boiling, sublimation, dissolving ammonium or potassium salts in water, heating of hydrated salt.

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