Nota kimia t4

1. Element – a substance consists of one type of atom.

2. Compound – a substance consists two or more elements that are chemically bonded(molecule or ions).

3. Atom – smallest particle of an element.

4. Molecule – a group of two or more atoms.

5. Ion – a positively charged / negatively charged particle.

6. Isotopes – atoms of the same element with same proton number but different nucleonnumbers.

7. Relative atomic mass of an element = the average mass of one atom of an element/((1/12) x the mass of one carbon-12

atom)

8. Relative molecular mass of an element = the average mass of one atom of an molecule/((1/12) x the mass of one carbon-

12 atom)

9. Molecule formula – compound shows the actual number of atoms of each element that are present in a molecule of the

compound

10. Empirical formula – compound shows the simplest whole number ratio of atoms of each element in the compound

11. Mole – amount of substance that contains as many particles as the number of atoms inexactly 12 g of carbon-12 the symbol

of mole is mol.

12. One mole – Avogadro constant – 6.02 x 1023

13. Group (Periodic Table) – vertical columns of element (similar chemical properties).

14. Periods (Periodic Table) – horizontal rows of element.

15. Valence electrons – electrons that occupy the outermost shell.

16. Ionic bond – bond formed through the transfer of electrons between atoms of metal andnon-metal to achieve the stable octet

electron arrangement.

17. Ionic compound – consist of positive ions and negative ions which are held by strong electrostatic forces of attraction.

18. Covalent bond – bond formed through the sharing of non-metal electrons to achieve the stable duplet or octet electron

arrangement.

19. Covalent compound (also simple molecular structure) – consists of neutral molecules which are held by weak

intermolecular forces (Van der Waals).

20. Alkali (base) – chemical substance which ionizes in water to produce hydroxide ions, OH-.

21. Acid – chemical substance which ionizes in water to produce hydrogen ions, H+ or hydroxonium ions, H3O+.

22. pH – degree of acidity or alkalinity of a solution. Scale ranges from 0 to 14.

23. pH value – measure of the concentration of hydrogen ions, H+.

24. Strong alkali – ionises (dissociates) completely in water to form hydroxide ions, OH- of high concentration.

25. Weak alkali – ionises (dissociates) partially in water to form hydroxide ions, OH- of low concentration.

26. Strong acid – ionises (dissociates) completely in water to form hydrogen ions, H+ of high concentration.

27. Weak acid – ionises (dissociates) partially in water to form hydrogen ions, H+ of low concentration.

28. Polymer – long chain molecules made up by monomer (repeating unit).

So there you go!!! 28 of the most common definitions for SPM Form 4 Chemistry.

Chemistry – earlier study of alchemy (an art of transforming common metals to precious metals, usually lead to

gold but to no success) (alchemy has since been proven to be a wrong and currently dead branch of science)

Chemistry – is the study of the composition, structure, properties and interactions of matter.

Founder of Modern Chemistry (try and read up on the history of these two great men)

1. Robert Boyle (1627-1691) – performed controlled experiments and published his work with elaborate details

such as procedure, apparatus and observations.

2. Antoine Lavoisier (1743-1794) – developed the Law of Conservation of Mass and thetheory of combustion.

Scientific Method

1. Making Observation

2. Making Inference (smart guess)

3. Identifying the Problem

4. Making a Hypothesis

5. Identifying the Variables

6. Controlling the Variables

7. Planning an Experiment

8. Collecting Data

9. Interpreting Data

10. Making a Conclusion

11. Writing a Report

Important Terms

Matter – anything that occupies space and has mass.

Compound – a substance consists two or more elements that are chemically bonded (molecule or ions).

Element – a substance that cannot be made into anything simpler by chemical reaction.

Atom – smallest particle of an element.

Molecule – a group of two or more atoms.

Ion – a positively charged / negatively charged particle.

Cations – positively-charge ions. Example: H+, K+, NH4+ and Mg2+

Anions – negatively-charge ions. Example: Br-, OH-, O2- and S2O32-

 

Velocity of the particle  increases when

Temperature  increases

Kinetic energy  increases

 

Diffusion – movement of particles from a region of high concentration to a region of lowconcentration.

Changes in the States of Matter

1. Freezing / Solidification – liquid -> solid

2. Melting – solid -> liquid

3. Evaporation – liquid -> gas / vapour

4. Condensation – gas / vapour -> liquid

5. Sublimation – gas / vapour -> solid

6. Sublimation – solid -> gas / vapour

(Sublimation – iodine, ammonium chloride and solid carbon dioxide)

 

Important Scientist and Their Contributions

Berry Berry Teacher thinks that it will be good if students can link the contribution of each great scientists to their findings. This

will allow a chronological understanding of the discoveries (for easier understanding) and to appreciate the work of these fine

scientist.

John Dalton (1808) – atomic theory

1. Atoms  – small indivisible particles.

2. Atoms – neither created nor destroyed.

3. Atoms – an element are alike.

4. Atoms – it combine in simple ratio.

5. Atoms – chemical reactions result from combination / separation of atoms.

J. J. Thomson (1897)

1. Electrons  – negatively-charged particles.

2. Atoms – positively-charged sphere.

Ernest Rutherford (1911)

1. Atoms – consists of a positively-charged nucleus with a cloud of electrons surrounding nucleus.

2. Protons  – positively-charged particles.

 

Niels Bohr (1913)

1. Electrons  – surrounding the nucleus (orbit).

James Cadwick (1932)

1. Neutrons  – electrically neutral subatomic particles.

2. Neutrons – mass almost the same with a proton.

3. Nucleus of an atom – consists of protons and neutrons.

Concepts of the Atomic Model

Modern Atomic Model

1. Nucleus of an atom – consists of protons and neutrons.

2. Electrons – moving around the nucleus (orbits / electron shells/ quantum shells)

 

Proton number / Atomic number / Number of protons

1. Number of protons in its atom.

2. Number of electrons (neutral atom).

Nucleon number / Mass number / Number of nucleon

1. Sum  of the number protons and neutrons.

 

Isotopes – atoms of the same element with same proton number but different nucleonnumbers.

(Further clarification on isotopes as there are still students who are confused with this concept – Isotopes for any elements simply

means that it is another element with the same number of proton and electron but different number of neutrons. It is important to

note that the atomic number of isotopes are the same, although the mass number is different. If you can understand this concept,

you should be okay)

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.

Posted by Cikgu Wong 0 comments Links to this postLabels: Chemistry

THURSDAY, NOVEMBER 3, 2011

Chemistry Form 4: Chapter 9 - Making of AlloyAn 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 CompositionSteel 99 %   iron     +   1 %  carbonStainless steel 74 %   iron  +  18 % chromium  +

8 % nickelBronze 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

Posted by Cikgu Wong 0 comments Links to this postLabels: Chemistry

SATURDAY, OCTOBER 22, 2011

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

Click on the diagram below to play!

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".

Posted by Cikgu Wong 2 comments Links to this postLabels: Chemistry

FRIDAY, OCTOBER 14, 2011

Chemistry Form 4: Chapter 9 - Haber Process1. 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 AmmoniaAmmonia 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

Click on the diagram below to play!

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 

Posted by Cikgu Wong 0 comments Links to this postLabels: Chemistry

WEDNESDAY, OCTOBER 12, 2011

Chemistry Form 5: Chapter 4 - Exothermic and Endothermic ReactionChemical 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

Bond breaking requires more energy than the energy that is released

breaking. 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.

Click on the diagram below to play!Posted by Cikgu Wong 0 comments Links to this postLabels: Chemistry

FRIDAY, SEPTEMBER 30, 2011

Chemistry Form 4: Chapter 7 - Determining the Molarity of Acid and Base Using Titration

Click on the diagram below to play!

Click on the diagram below to play!Posted by Cikgu Wong 0 comments Links to this postLabels: Chemistry

WEDNESDAY, SEPTEMBER 28, 2011

Chemistry Form 4: Chapter 7 - Neutralization Reaction

As you can see from the equations, acids release H+ into solution and bases release OH-. If we were to mix an acid and base together, the H+ ion would combine with the OH- ion to make the molecule H2O, or plain water:

H+(aq) +   OH-

(aq)   H2ONeutralization is a reaction between acid and base to produce salt and water only as shown below: 

Acid Base Water Salt

HCl  +  NaOH   H2O  +  NaCl

HBr  +  KOH   H2O  +  KBr

Uses of neutralization1. Soil treatment - if the soil is too acidic, it is treated with a base in order to neutralise it. Common treatments use quicklime (calcium oxide) or chalk (calcium carbonate). 

2. Indigestion -  too much hydrochloric acid in our stomach leads to indigestion. Therefore, to cure this ailment we need to neutralise the acid with a base such as, sodium hydrogen carbonate (baking soda), or milk of magnesia. 

3. Bee sting contains acid -  In order to relieve the painful symptoms of the sting we need to neutralise the acid. By rubbing on calamine lotion(zinc carbonate) or baking soda the acid can be neutralised.

4. Wasp sting contains alkaline -  Hence acid is needed to neutralise and remove the painful sting. Vinegar (ethanoic acid) is used.

Posted by Cikgu Wong 0 comments Links to this postLabels: Chemistry

MONDAY, SEPTEMBER 19, 2011

Chemistry Form 4: Chapter 7 - pH Scale

The pH scale is used to measure degree of the acidity or alkalinity of an aqueous solution based on the concentration of hydrogen ions. pH is defined as the concentration of hydrogen ions in solution.

Click on the diagram below to play!

1. The higher the concentration of H+ , the lower the pH value.

2. The higher the pH value, the higher the concentration of hydroxide ions.

3. At pH =7, the concentration of H+ ions is equal to the concentration of OH- . The solution is termed as being neutral for example pure water.

4. The stronger an acid, the lower of its pH value.

5. The stronger an alkali, the higher of its pH value.

Click on the diagram below to play!

Posted by Cikgu Wong 0 comments Links to this postLabels: Chemistry

SUNDAY, SEPTEMBER 11, 2011

Chemistry Form 4: Chapter 7 - Strength of AlkaliThe strength of alkali depends on the degree of dissociation of the alkali in water to produce hydroxide ions. The pH of an alkali solution depends on the concentration of hydroxide ions.

Strong Alkali Weak Alkali     Strong alkali have a higher

degree of dissociation.     A strong alkali is an alkali

whichdissociates completely in water to produce a high concentration of hydroxide ions.

     Thus, pH value for strong alkali is higher than weak alkali.

     Weak alkali have a lower degree of dissociation.

     A weak alkali is an alkali whichionises partially in water to produce a low concentration of hydroxide ions. Only a part of the molecules ionises and the remaining still in covalent molecules.

     Thus, pH value for weak alkali is lower than strong alkali.

Click on the diagram below to play!

Posted by Cikgu Wong 0 comments Links to this postLabels: Chemistry

SATURDAY, SEPTEMBER 10, 2011

Chemistry Form 4: Chapter 7 - How to Differentiate Between Strong Acid and Weak AcidA) Reaction between acids and reactive metals

Strong acids can react with reactive metal faster and more vigorously. More hydrogen gas produced at a faster rate.

Weak acids can react with reactive metal slower and less vigorously. Less hydrogen gas produced at a slower rate.

B) Electrical conductivity 

 

Conductivity Behavior of Acids 

 Compounds Appearance of light bulb

 ClassificationWeak or Strong

 Inference of Ions or Molecules

 water, H2O  no light  weak  molecules hydrochloric acid, HCl  bright  strong  ions

  acetic acid, HC2H3O2  dim  weakmostly molecules, less ions

Strong acids able to conduct electricity better as shown in hydrochloric acid because it contains a large number of freely moving ions as strong acids dissociate completely in water.

Weak acids conduct electricity weakly as shown in acetic acid because it contains a few number of moving ions as weak acids dissociate partially in water. Most of weak acids still remain in covalent molecule.

Posted by Cikgu Wong 0 comments Links to this postLabels: Chemistry

SUNDAY, AUGUST 28, 2011

Chemistry Form 4: Chapter 7 - Preparing a Standard Solution

Standard solution is a solution whose concentration is known accurately.

The solution is normally expressed in mol dm-3

Standard solution can be prepared by using a calculated mass of solute or dilution method from concentrated solution.

MAKING STANDARD SOLUTIONS FROM CONCENTRATED AQUEOUS

Equipment typically used when preparing a solution in a volumetric flask includes the volumetric flask and its glass stopper, pipette, a medicine dropper, and a funnel. Water can be delivered from the beaker or wash bottle.

Procedure:

MAKING STANDARD SOLUTIONS FROM CALCULATED MASS

Procedure:

Volumetric flask is more accurate than beaker for the preparation of standard solution.

Water is added using dropper to bring the solution to the graduation mark.

Standard solution must be covered by stopper to prevent the contamination of the standard solution by foreign particles.

After preparing the standard solution, shake it well to ensure thorough mixing.

Posted by Cikgu Wong 0 comments Links to this postLabels: Chemistry

SUNDAY, AUGUST 21, 2011

Chemistry Form 5: Chapter 3 - Conversion of Iron (II) to Iron (III) and Iron (III) to Iron (II)

Conversion of Fe2+ to Fe3+

Oxidising agent : bromine waterReducing agent :  Fe2+ ions

Oxidation half equation: Fe2+ ions lose electrons and are oxidized to Fe3+.

The presence of Fe3+ ions is confirmed by the formation of brown precipitate with excess of NaOH solution.

                     Fe2+ -------->    Fe3+    +     e

Reduction half equation: Bromine molecules which give bromine water its brown colour gain electrons and are reduced to colourless bromide ions.

                     Br2    +    2 e   ------->  2 Br-

Overall ionic equation:

2 Fe2+   +    Br2      2 Fe3+    +    2 Br-

Observation: Brown bromine water decolourises. The solution changes colour from pale green (Fe2+)  to yellow (Fe3+).

Conversion of Fe3+ to Fe2+

Oxidising agent : Fe2+ ionsReducing agent :  zinc

Oxidation half equation : Zinc atoms lose their electrons and are oxidized to zinc ions, Zn2+.

Zinc powder dissolves in iron (III) chloride.

Zn    ------->   Zn2+    +    2 e

Reduction half equation: Fe3+ ions accept electrons and are reduced to Fe2+.

The presence of Fe2+ ions is confirmed by the formation of green precipitate with excess of NaOH solution.

Fe3+    +     e        Fe2+   

Overall ionic equation:

2 Fe3+   +    Zn    --------->  2 Fe2+    +    Zn2+

Observation: Zinc powder dissolves into solution. The solution changes

colour from brown (Fe3+) to pale green (Fe2+).

Posted by Cikgu Wong 0 comments Links to this postLabels: Chemistry

THURSDAY, AUGUST 18, 2011

Chemistry Form 4: Chapter 7 - Strength of AcidThe strength of an acid depends on the degree of dissociation of the acid in water to produce hydrogen ions and anions. The pH of an acid solution depends on the concentration of hydrogen ions.

Strong Acid Weak Acid     Strong acid have a higher degree of

dissociation.     A strong acid is an acid

whichdissociates completely in water to produce a high concentration of hydrogen ions.

     Thus, pH value for strong acid is lower than weak acid.

     Weak acid have a lower degree of dissociation.

     A weak acid is an acid whichionises partially in water to produce a low concentration of hydrogen ions. Only a part of the molecules ionises and the remaining still in covalent molecules.

     Thus, pH value for weak acid is higher than strong acid.

Click on the diagram below to play!

Weak Acid

Strong Acid

Examples of strong acid

HCl     Hydrochloric acid     HNO3   Nitric acid

HBr     Hydrobromic acid    H2SO4   Sulfuric acid

HI      Hydroiodic acid      HClO4  Perchloric acid

Examples of weak acid

Posted by Cikgu Wong 2 comments Links to this postLabels: Chemistry

SUNDAY, AUGUST 7, 2011

Chemistry Form 4: Chapter 7 - Concentration of Solution (Molarity) Molarity is defined as moles of solute per liter or 1 dm3 of solution.

Molarity is used to express concentration of solution.

1 dm3 = 1000 cm3

The unit of molarity is mol dm-3

Click on the diagram below to play!

Posted by Cikgu Wong 0 comments Links to this postLabels: Chemistry

THURSDAY, AUGUST 4, 2011

Chemistry Form 4: Understanding of Acid and Bases

Acid is a chemical substance thatdissolves in water to produce hydrogen ions, H+ ions. This causes the concentration of hydrogen ion in the solution to increase and thepH to drop.

According to the Arrhenius definition, when hydrogen chloride which is a gas HCl is dissolved in water, it dissociates to produce hydrogen ions and chloride ions in solution. This making HCl an acid when dissolves in water.

Without presence of water, the acid will not dissociate to produce hydrogen ions and it will not show acidic properties.---------------------------------------------------------------------------------------------------

Also, a base is a chemical substance that dissolves in water to produce hydroxide ions, OH- ions. This causes the concentration of hydroxide ion in the solution to increase but decrease in concentration of hydrogen ion. This is why the pH increases when a base is added to water.

According to Arrhenius definition, sodium hydroxide, NaOH is a base because when it dissolved in water, the NaOH dissociates to produce hydroxide ions.

Without presence of water, the base will not dissociate to produce hydroxide ions and it will not show basic properties.

                                                 Acid                                       Base

OperationalDefinition

When added to water

pH < 7

When added to water

pH > 7

ArrheniusDefinition

When added to water

dissociates to release

a hydrogen ion (H+)

When added to water

dissociates to release

a hydroxide ion (OH-)

The Swedish Chemist, Svante Arrhenius (1859-1927). The Arrhenius definition of acids and bases is an extension of his theory of electrolyte solution, which formed his 1884 doctoral thesis.

Posted by Cikgu Wong 0 comments Links to this postLabels: Chemistry