Similarities and differences between alkanes and alkenes

SIMILARITIES:

• Both are insoluble in water
• Both are neutral
• Both burn in excess air to produce carbon dioxide and water.

DIFFERENCES:

Alkanes:

• General formula: C_nH_2n+2
• Saturated hydrocarbon
• Do not decolourise the purple acidified potassium manganate (VII) solution.
• Do not decolourise the reddish-brown bromine solution.
• Burn with a less sooty flame because the percentage by mass of carbon is lower than that of the corresponding alkenes. 

Alkenes

• General formula: C_nH_2n
• Unsaturated hydrocarbon
• Decolourise the purple acidified potassium manganite (VII) solution.
• Decolourise the reddish-brown bromine solution.
• Burn with a more sooty flame because the percentage by mass of carbon is higher than that of the corresponding alkanes. 

SPM Form 5: Rate of reaction (Checklist)

• Rate of reaction: The decrease in the amount of reactant used or the increase in the amount of product obtained in a given time. The rate of reaction measures how much product is formed in a certain time. Some reactions are slow, such as rusting, and some are fast, like burning.
• Average of reaction: The average value of the rate of reaction within a specified period of time.
• Rate of reaction at a given time: The actual rate of reaction at a specific time.
• Collision theory: A model that explains reaction rate as the result of particles colliding with a certain minimum energy.
• Effective collision: A collision in which the particles meet with sufficient energy and an orientation that allows them to react.
• The rate of reaction decreases with the increase of time.
• The rate of reaction increases as the total surface area of a solid reactant increases.
• The rate of reaction increases as the concentration of reactant increases.
• The rate of reaction increases as the temperature of a reactant increases.
• The rate of reaction increases when a positive catalyst is used and the rate of reaction increases when the amount of a positive amount used increases.
• Catalyst: A substance which alters the rate of a chemical reaction while it remains chemically unchanged at the end of the reaction. 

Soap vs Detergent: Similarities and Differences

Similarities:

• Both are cleansing agents.
• Each ion of both soap and detergent consists of a long chain of hydrocarbon part which is hydrophobic and an ionic part which is hydrophilic.
• Both can reduce the surface tension of water, thus, allowing water to wet the surface.
• The cleansing actions of both soap and detergent enable oil droplets to disperse in water and form an emulsion that will not redeposit on the surface.
• Both are effective as cleansing agents in soft water.

Differences:

• Soap is biodegradable while detergent is not biodegradable (can cause environmental pollution).
• Detergent is an effective cleansing agent in hard water, soft water and in acidic solution but soap is only effective as a cleansing agent in soft water.

SPM Chemistry Form 4 and Form 5: Checklist (Definitions)

Form 4:

Chapter 1: Introduction to Chemistry

Chapter 2: The Structure of the Atom

Chapter 3: Chemical Formulae and Equations

Chapter 4: Periodic Table of Elements

Chapter 5: Chemical Bonds

Chapter 6: Electrochemistry

Chapter 7: Acids and Bases

Chapter 8: Salts

Chapter 9: Manufactured Substances in Industry

Form 5:

Chapter 1: Rate of Reaction

Chapter 2: Carbon compounds

Chapter 3: Oxidation and reduction

Chapter 4: Thermochemistry

Chapter 5: Chemical for Consumers

SPM Form 4: Salts (Checklist)

• Salts: An ionic compound formed when the hydrogen ion in an acid is replaced by a metal ion or an ammonium ion. Salts are formed as the product of an acid reaction with an alkali. Soluble salts dissolve in water. Insoluble salts do not dissolve in water.
• Recrystallization: A technique used to purify crystals of a soluble salt by carrying out the crystallization process again on these crystals.
• Precipitation reaction: A reaction which involves the reaction between two aqueous reactants to form an insoluble substance.
• Continuous variation method: An experiment which involves the reaction of a solution at fixed volume and another solution with volumes that varies uniformly.
• All carbonate salts are decomposed on heating to liberate carbon dioxide gas, CO₂ except sodium carbonate, Na₂CO₃ and potassium carbonate, K₂CO₃.
• All nitrate salts are decomposed on heating to liberate nitrogen dioxide gas, NO₂ and oxygen gas, O₂ except sodium nitrate, NaNO₃ and potassium nitrate, KNO₃ which liberate oxygen gas, O₂ only.
• The presence of carbonate ions can be confirmed by adding dilute acids.
• The presence of sulphate ions can be confirmed by adding acidified barium chloride, BaCl₂ solution.
• The presence of chloride ions can be confirmed by adding acidified silver nitrate, AgNO₃ solution.
• The presence of nitrate ions can be confirmed by adding dilute sulphuric acid, H₂SO₄ followed by iron (II) sulphate, FeSO₄ solution and a little concentrated sulphuric acid, H₂SO₄.
• The identify of cation can be determined by using sodium hydroxide, NaOH solution and ammonia, NH2 solution except aluminium ion, Al³⁺ and lead (II) ion, Pb²⁺.
• Ammonium ion can be tested by heating with a strong alkali or adding Nessler’s reagent.
• Iron (II) ion and iron (III) ion can be tested by using potassium hexacyanoferrate (II), K₄Fe(CN)₆ solution, potassium hexacyanoferrate (III), K₃Fe(CN)₆ or potassium thiocyanate, KSCN solution.
• Lead (II) ions can be tested by using potassium iodide, KI solution.

SPM Form 4: Manufactured Substances in Industry (Checklist)

• Sulphuric acid (H₂SO₄) is a highly corrosive acid made from sulfur dioxide; widely used in the chemical industry.
• Contact process: the industrial process for making sulfuric acid.
• Ammonia (NH₃) is colorless, pungent gas composed of nitrogen and hydrogen.

• Haber process: the process for making ammonia from nitrogen and hydrogen, in industry.
• Ammonium fertilizer: A salt that is prepared from the reaction between ammonia and an acid. Ammonium sulphate, (NH₄)₂ SO₄ which is an ammonium fertilizer can be prepared from the reaction between ammonia, NH₃ solution and sulphuric acid, H₂SO₄.
• Alloys: A mixture of two or more elements with certain fixed composition in which the major component is a metal. Alloy is harder than pure metal.
• Metal corrosion: The gradual destruction of a metal by reaction with its environmental. Iron rusts faster than steel. Stainless steel does not rust.
• Polymer: a compound containing very large molecules, formed by polymerization.
• Synthetic polymers are derived from petroleum oil, and made by scientists and engineers. Examples of synthetic polymers include nylon, polyethylene, polyester, Teflon, and epoxy.
• Natural polymers occur in nature and can be extracted and often water-based. Examples of naturally occurring polymers are silk, wool, DNA, cellulose and proteins.
• Glass: A homogeneous material with a random, liquid-like molecular structure.
• Ceramic is a hard, unreactive material that can withstand high temperatures, made by baking clay in a kiln; ceramics are non-conductors.
• A "composite" material is when two or more different materials are combined together to create a superior and unique material.

SPM Form 4: Periodic Table of elements (Checklist)

• Periodic Table: the table showing the elements in order of increasing proton number; similar elements are arranged in columns called groups.
• Group: A vertical column of elements in the Periodic table.
• Period: A horizontal row of the Periodic Table; its number tells you how many electron shells there are.
• Alkali metals: the Group I elements of the Periodic Table, which include lithium, sodium, potassium, rubidium, caesium and francium.
• Alkaline earth metals: the Group II elements of the Periodic Table, which include beryllium, magnesium, calcium, strontium, barium, and radium.
• Halogens: the Group VII elements of the Periodic Table, which include fluorine, chlorine, bromine, iodine and astatine.
• Noble gases: the Group 18 elements of the Periodic Table; they are called ‘noble’ or inert gases because they are so unreactive, which include helium, neon, argon, krypton, xenon and radon.
• Transition elements: the elements in the wide middle block of the Periodic Table (elements in group 3 to group 12).
• Metal: an element that shows metallic properties (for example conducts electricity, and forms positive ions)
• Non-metal - an element that does not show metallic properties: the non-metals lie to the right of the zig-zag line in the Periodic Table.
• Amphoteric oxide: An oxide that exhibits both acidic and basic properties.
• The atomic radius is a term used to describe the size of the atom.
• The ionization energy is the energy required to completely remove an electron from a gaseous atom or ion.
• Electron affinity reflects the ability of an atom to accept an electron. It is the energy change that occurs when an electron is added to a gaseous atom.
• Electronegativity is a measure of the attraction of an atom for the electrons in a chemical bond. The higher the electronegativity of an atom, the greater its attraction for bonding electrons.

Uses of the noble gases

The noble gases are unreactive or inert, which makes them safe to use. They also glow when a current is passed through them at low pressure. These properties lead to many uses:

• Helium is used to fill balloons and airships, because it is much lighter than air – and will not catch fire.
• Argon is used to provide an inert atmosphere. For example it is used: as filler in tungsten light bulbs and to protect metals that are being welded.
• Neon is used in advertising signs. It glows red, but the colour can be changed by mixing it with other gases.
• Krypton is used in lasers – for example for eye surgery – and in car headlamps.
• Xenon gives a light like bright daylight, but with a blue tinge. It is used in lighthouse lamps, lights for hospital operating rooms, and car headlamps.

Discuss the advantages and disadvantages of aspirin as a medicine

Advantages

• It is used to relieve pain such as arthritic pain, dental pain, etc where there is an inflammation involved.
• It is used to prevent thickening of blood and heart attack.

Disadvantages

• It is acidic and can cause internal bleeding and ulceration in the stomach. 

Explain the reactivity of halogens decreases when going down Group 17.

The atomic size of halogen increases when going down Group 17. Thus, the outermost occupied shell becomes further away from the nucleus. Hence, the strength of the nucleus to pull another electron into the outermost occupied shell becomes weaker. Thus, halogens are less reactive when going down Group 17. 

Explain how the melting and boiling points change when going down the Group 1.

Melting and boiling points of alkali metals decreases when going down Group 1. The atomic size of alkali metals becomes bigger when going down the group 1. Hence, the forces between alkali metal atoms are weaker when going down Group 1. Hence, less heat energy is required to break the weaker forces.

Why noble gases chemically inert?

Helium has a duplet electron arrangement whereas other noble gases have octet electron arrangements. These electrons arrangements are very stable. Hence, atoms of noble gases do not release electrons, accept electrons or share electrons with other atoms. Thus, they are chemically inert. 

Why is neon exists as a monoatomic gas?

• Neon is from the Noble Gases group on the periodic table. 
• Neon has electron arrangement is 2.8 (valence electron is 8). 
• Neon already achieves the octet electron arrangement. 
• Neon does not need to donate the electron with other element. 
• Therefore they do not gain or lose electrons making them exist as individual atoms. 
• Neon exists as a monoatomic gas. 

Kinetic Molecular Theory

• Matter consists of small particles that always move and collide among each other.
• The kinetic theory of matter stated the particles move freely when energy is absorb and move slowly when energy is release, then they are cooled.
• The kinetic molecular theory used to explain the change physical state of matter.
• Gas molecules are individual particles that travel in a straight-line random motion. This will continue until they collide or are acted upon by another force.
• Gas molecules continuously collide and transfer energy during these collisions. In an isolated sample of gas the net energy is conserved.
• The volume of the individual gas molecules is negligible compared to the volume they occupy.
• No forces of attraction are considered to exist between the gas molecules.

Common Methods to Synthesize Ketones

Ketones are prepared from 2° alcohols, acid chlorides, and alkynes.

Common Methods to Synthesize Aldehydes

Aldehydes are prepared from 1° alcohols, esters, acid chlorides, and alkynes.

The basic principles of resonance

The basic principles of resonance:

• Resonance exists when a compound cannot be represented by a single Lewis structure.
• Resonance structures differ in the position of only non-bonded electrons and π bonds, not atoms.
• The resonance hybrid is the only accurate representation for a resonance-stabilized compound. A hybrid represents the compound better than any single resonance structure because electron density is delocalized.

Common names of Alkyl Groups

Factors That Determine Acidity

• Element effects: The acidity of H – A increases both left-to-right across a row and down a column of the periodic table.
• Inductive effects: The acidity of H– A increases with the presence of electron-withdrawing groups in A.
• Resonance effects: The acidity of H– A increases when the conjugate base A:– is resonance stabilized.
• Hybridization effects: The acidity of H – A increases as the percent s-character of A:– increases.

Rate of reaction calculation formula

Acid and Base calculations formula

Atomic Radius - trends on periodic table

Generally, the atomic radius decreases across a period from left to right and increases down a given group.

Moving from left to right across a period, electrons are added one at a time to the outer energy shell. Electrons within a shell cannot shield each other from the attraction to protons. Since the number of protons is also increasing, the effective nuclear charge increases across a period. This causes the atomic radius to decrease.

Moving down a group in the periodic table, the number of electrons and filled electron shells increases, but the number of valence electrons remains the same. The outermost electrons in a group are exposed to the same effective nuclear charge, but electrons are found farther from the nucleus as the number of filled energy shells increases. Therefore, the atomic radii increase.

Endothermic reaction

• Endothermic reaction describes a process which absorbs thermal (heat) energy.
• ∆H = positive
• Products contain more energy than the reactants. E₂ > E₁
• Heat energy is absorbed from the surroundings and is converted to chemical energy during the reaction. This increases the energy contents of the products.
• Total heat energy given out during the formation of chemical bonds < Total heat energy absorbed during the breaking of chemical bonds.
• Temperature of the surroundings decreases i.e. the reacting mixture becomes cold. 

Exothermic reaction

• Exothermic reaction: a chemical reaction that produces heat.
• ∆H = negative
• Reactants contain more energy than the products. E₁ > E₂
• Chemical energy decreases during the reaction and is converted to heat energy (heat is given out).
• Total heat energy given out during the formation of chemical bonds > Total heat energy absorbed during the breaking of chemical bonds.
• Temperature of the surroundings increases i.e. the reacting mixture becomes hot.  

Why does the atomic size decreases when going across Period 2?

When going across Period 2, the positive charge of the nucleus of the elements increases, atoms of elements in Period 2 have two shells occupied with electrons. Hence, the increasing positive charge of the nucleus pulls the two shells of electrons closer to the nucleus when going across Period 2. This causes the decreases in the atomic size.  

Why the boiling point of noble gases increases when going down the group?

The boiling point of noble gases increases when going down Group 18. This is because the atomic size of noble gases becomes bigger when going down Group 18. Thus, the forces of attraction between atoms become stronger when going down Group 18. More heat energy is required to overcome the forces between atoms. This causes the boiling point of noble gases to increases when going down Group 18. 

Predict the physical and chemical properties of astatine

Predict the physical and chemical properties of astatine. Astatine is placed below iodine in Group 17 of the Periodic Table.

 

Physical properties of astatine:

• Black solid
• Has low melting and boiling points
• Has a low density
• Cannot conduct electricity
• Poor conductor of heat
• Slightly soluble in water

Chemical properties of astatine:

• Astatine reacts with cold sodium hydroxide solution to form sodium astatide, sodium astatate (I) and water.

At_{2 (s)} + 2NaOH _(aq) → NaAt _(aq) + NaOAt _(aq) + H₂O _(l)

• Astatine vapour reacts with heated iron wool to form a brown solid of iron wool to form a brown solid of iron (III) astatide.

2Fe _(s) + 3At_{2 (g)} → 2FeAt_{3 (s)}

Whats the difference between atoms of oxygen-16 and oxygen-17?

Oxygen-16 and Oxygen-17 are two isotopes of oxygen.  Isotopes are atoms of the same element with same number of protons but different numbers of neutrons. Both atoms have the same number of protons and electrons. Oxygen-16 has 8 neutrons whereas oxygen-17 has 9 neutrons. Oxygen-16 has a nucleon number of 16 whereas oxygen-17 has a nucleon number of 17. 

Reactions of acids

• Reacts with alkali to form → salt + water (neutralization)
• Reacts with metals to form → salt + hydrogen gas
• Reacts with oxide metals to forms → salt + water
• Reacts with carbonate metals to form → salt + CO₂ + water

Properties of base

• Bitter taste
• Feels slippery
• Conducts electric current
• Turns litmus paper blue
• Reacts with acids to produce salts and water

Properties of acid

• Sour taste
• Conducts electricity
• Turns litmus paper red
• Reacts with bases to produce salts and water
• Reacts with some metal sand releases hydrogen gas

The role water in showing the properties of alkalis

An alkali will only exhibits show its alkaline properties when it is dissolved in water.

Presence of water

Molecules in alkali will ionize to hydroxide ions

An alkali wills only exhibits show its alkaline properties when it is dissolved in water 

(the presence of hydroxide ions)

Without the presence of water

Alkali remain in the form of molecules

Cannot ionize to hydroxide ions

No free moving hydroxide ions

Example:  In pure dry power state, the hydroxide ions in barium hydroxide, Ba(OH)₂ powder are arranged orderly at fixed positions. Hence, dry barium hydroxide, Ba(OH)₂ powder does not exhibit alkaline properties. In aqueous state, barium hydroxide, Ba(OH)₂ dissolves and ionizes completely to produce free mobile hydroxide ions. Hence, barium hydroxide Ba(OH)₂ solution can exhibit alkaline properties.

The role water in showing the properties of acids

An acid will only show its acidic properties when it is dissolved in water.

Presence of water

Molecules in acids will ionize to hydrogen ions

An acid will only show its acidic properties when it is dissolved in water (the presences of hydrogen ions)

Without the presence of water

Cannot ionize to hydrogen ions

No free moving hydrogen ions

Acids remain in the form of molecules

Example: Ethanoic acid, CH₃COOH only exhibits acidic properties when water is present. It does not show acidic properties in pure dry liquid state or in dry propanone. In pure dry liquid state or in dry propanone, ethanoic acid, CH₃COOH remains as covalent molecules. No hydrogen ions are present, thus it does not exhibit acidic properties. In aqueous state or when water is present, ethanoic acid, CH₃COOH solution ionizes partially to produce free mobile hydrogen ions. Hence, it exhibits acidic properties. Water causes the molecules of CH₃COOH to ionize partially to produce free mobile hydrogen ions that give rise to the acidic properties of ethanoic acid, CH₃COOH.

Isotopes Definition

Isotopes are atom of same element that has same proton number but different nucleon number. In other words, they have different atomic weights. Isotopes are different forms of a single element.

pH Definition

pH is a measure of hydrogen ion concentration; a measure of the acidity or alkalinity of a solution.

• pH of 7.0: Neutral
• pH below 7.0: Acid
• pH above 7.0: Alkaline

Overview of Periodic Table

• Alkali Metals (Group 1) : All group 1 metals have one valence electron. When they form ions, they will have a charge of 1+. Group 1 alkali metals are highly reactive and will react vigorously with water.

• Alkali Earth Metals (Group 2): All group 2 metals have two valence electrons. When they form ions, they will have a charge of 2+. Group 2 alkaline earth metals are highly reactive and will react with water.

• Transition Metals (Groups 3–10, d block): Transition metals are famous for the colored salts and colored solutions they form. Many gems contain numerous transition metals. It is hard to predict the charge of a transition metal ion because the transition metals have multiple oxidation states. One transition metal, Hg, exists as a liquid at room temperature.

• Halogens (Group 17): Halogens (salt formers) have seven valence electrons and form ions with a charge of 1−. The halogens exist in three phases at room temperature. Fluorine is a pale-yellow gas, chlorine is a green gas, bromine is a brown-orange liquid, and iodine is a purple solid.

• Noble (Inert) Gases (Group 18): Noble gases have a full outer shell and will not react to form ions or share electrons.

• Lanthanides and Actinides (f Block): These elements have their valence electrons located in the f orbitals and are radioactive in nature.

The alkali metals - trends in reactivity

As you go down the group, the atomic number of the alkali metals increases, and their properties change:

• their melting points decrease
• their densities increase
• they become softer
• they become more reactive

The alkali metals are soft, reactive metals. They react vigorously with water and become more reactive as you go down the group.

What is pKa and pKb ?

pK_a definition: pK_a is the negative base-10 logarithm of the acid dissociation constant of a solution.
pKa = -log₁₀K_a
The lower the pKa value, the stronger the acid.

pK_b definition: pK_b is the negative base-10 logarithm of the base dissociation constant of a solution.
pKb = -log₁₀K_b
The lower the pK_b value, the stronger the base.