Redox
Definition: reactions which both oxidation and reduction reactions take place at the same time.
Oxidation
Gain in oxygen
Lose of electrons
Lose of hydrogen
Increase in oxidation state number
Reduction
Lose of oxygen
Gain of electrons
Gain in hydrogen
Decrease in oxidation state number
Fixed Oxidation numbers
0
All elements, noble gases, metals
+1
Group 1 ions, H+
+2
Group 2 ions
+3
Al3+
-1
Group 7 ions, Oxygen in H2O2, hydrogen in Metal hydrides e.g NaH
-2
O2-, S2-.
-3
Nitrides N3-
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Json Lim
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Wednesday, September 30, 2009
Rate of Reaction
Rate of reactions
Rate of reaction can be calculated and compare by measuring a loss of mass or amount of gas collected.
Factors affected rate of reaction
• Particle size
• Temperature
• Pressure (only for all gas system)
• Catalyst
• Concentration
Use this standard statement to answer your question.
Increase in temperature leads to an increase in the energy of the particles which leads to an increase in number of collisions. This leads to an increase in number of effective collisions which leads to an increase in rate of reaction. The Itallic and bold words can be change to accommodate the factors.
e.g. Increase in particle sizes leads to an increase in the surface area of the reagent which leads to an increase in number of collisions. This leads to an increase in rate of reaction which leads to an increase in rate of reaction. GOT IT? When plotting graphs, the number of moles of products determine the end point of the reaction!
Enjoy!
Entry by
Json Lim
http://www.oleveltuition.com/
Rate of reaction can be calculated and compare by measuring a loss of mass or amount of gas collected.
Factors affected rate of reaction
• Particle size
• Temperature
• Pressure (only for all gas system)
• Catalyst
• Concentration
Use this standard statement to answer your question.
Increase in temperature leads to an increase in the energy of the particles which leads to an increase in number of collisions. This leads to an increase in number of effective collisions which leads to an increase in rate of reaction. The Itallic and bold words can be change to accommodate the factors.
e.g. Increase in particle sizes leads to an increase in the surface area of the reagent which leads to an increase in number of collisions. This leads to an increase in rate of reaction which leads to an increase in rate of reaction. GOT IT? When plotting graphs, the number of moles of products determine the end point of the reaction!
Enjoy!
Entry by
Json Lim
http://www.oleveltuition.com/
Energy Changes
Energy Changes
Enthalpy change is the amount of heat released or absorbed when a chemical reaction occurs.
Exothermic reaction – liberates heat energy to the surroundings which results in a general increase in the temperature of the surroundings.
Endothermic reaction – absorbs heat energy to the surroundings which results in a general decrease in the temperature of the surroundings.
Type of reactions Enthalpy Product energy level
Exothermic
ΔH= - ve because more heat is given out during bond forming than heat taken in to break them
Product is at a lower energy compared to reagent.
Bonds of products are stronger than bonds in reagent.
Endothermic
ΔH=+ ve because more heat is taken in to break bonds than heat is given out when bonds form.
Product is at a higher energy compared to reagent.
Bonds of reactants are stronger than products.
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Json Lim
http://www.oleveltuition.com/
Enthalpy change is the amount of heat released or absorbed when a chemical reaction occurs.
Exothermic reaction – liberates heat energy to the surroundings which results in a general increase in the temperature of the surroundings.
Endothermic reaction – absorbs heat energy to the surroundings which results in a general decrease in the temperature of the surroundings.
Type of reactions Enthalpy Product energy level
Exothermic
ΔH= - ve because more heat is given out during bond forming than heat taken in to break them
Product is at a lower energy compared to reagent.
Bonds of products are stronger than bonds in reagent.
Endothermic
ΔH=+ ve because more heat is taken in to break bonds than heat is given out when bonds form.
Product is at a higher energy compared to reagent.
Bonds of reactants are stronger than products.
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Json Lim
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Electrolytes
5 types of electrolysis systems
• Molten salt – the 2 ions will discharge
• Aqueous salt – hydrogen (unless metal is below hydrogen in that case the metal will discharge) and hydroxide ions (ALWAYS) will discharge
• Acidic solution - hydrogen and hydroxide ions will discharge
• Concentrated chlorides solution – ALWAYS chloride ions, positive ions the usual method of looking at reactivity series of methods for discharge order.
• Reactive anode (used in the purification of copper or electroplating) – anode dissolves into the solution. UNDER NO CIRCUMSTANCES will cathode dissolve. Even in simple cells the plate that dissolve (i.e. the more reactive plate that dissolves in the anode).
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• Molten salt – the 2 ions will discharge
• Aqueous salt – hydrogen (unless metal is below hydrogen in that case the metal will discharge) and hydroxide ions (ALWAYS) will discharge
• Acidic solution - hydrogen and hydroxide ions will discharge
• Concentrated chlorides solution – ALWAYS chloride ions, positive ions the usual method of looking at reactivity series of methods for discharge order.
• Reactive anode (used in the purification of copper or electroplating) – anode dissolves into the solution. UNDER NO CIRCUMSTANCES will cathode dissolve. Even in simple cells the plate that dissolve (i.e. the more reactive plate that dissolves in the anode).
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Json Lim
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Intermolecular Forces and Intramolecular forces for Graphite
Note for graphite, both covalent and intermolecular force of attraction applies. (Pure)
When explaining the high temperature in which graphite melts, we say that they are breaking strong covalent bonds. (Pure)
When explaining why graphite act like a lubricant, we say that the graphite molecules are arranged in layers which are held by weak IMF therefore can slide over each other easily. GET IT? (Pure)
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Json Lim
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When explaining the high temperature in which graphite melts, we say that they are breaking strong covalent bonds. (Pure)
When explaining why graphite act like a lubricant, we say that the graphite molecules are arranged in layers which are held by weak IMF therefore can slide over each other easily. GET IT? (Pure)
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Json Lim
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Bonding
Bonding and Structures
Chemical bond is a force of attraction holding atoms together in a molecule or crystal
Three types of chemical bonds
• Ionic bonding
• Covalent bonding
• Metallic bonding
Ionic bonding – involving metal and non-metal elements. Force of attraction between oppositely charged ions. Only exception is compounds like ammonium salts. Although ammonium is made up entirely of NON_METAL, it is still an Ionic compound because it contains charges.
Covalent bond – formed between 2 combining atoms of non-metallic by mutual sharing of one or more electrons
Metallic bonding – type of chemical bond that holds the atoms together in a solid metal. It’s the attraction between the sea of electrons and the positive metal ions. (more important for pure chem.)
Covalent compounds
- simple molecular compounds like hydrogen molecule, water molecule etc.
- giant molecular structure like diamonds and silicon dioxide (pure)
- graphite
Ionic compounds – self explanatory
Metallic substances – pure metals and alloys
Types of substances
Simple molecular
Types of bonds broken during change of state: Intermolecular forces of attraction.
Strength of the bond broken:Weak
Melting point and Boiling point:Low
Giant molecular or Giant Covalent
Types of bonds broken during change of state:Covalent
Strength of the bond broken:Strong
Melting point and Boiling point:High
Ionic Compounds
Types of bonds broken during change of state:Ionic Bonds
Strength of the bond broken:Strong
Melting point and Boiling point:High
Metals Types of bonds broken during change of state:Metallic Bonds
Strength of the bond broken:Strong
Melting point and Boiling point:High
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Json Lim
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Chemical bond is a force of attraction holding atoms together in a molecule or crystal
Three types of chemical bonds
• Ionic bonding
• Covalent bonding
• Metallic bonding
Ionic bonding – involving metal and non-metal elements. Force of attraction between oppositely charged ions. Only exception is compounds like ammonium salts. Although ammonium is made up entirely of NON_METAL, it is still an Ionic compound because it contains charges.
Covalent bond – formed between 2 combining atoms of non-metallic by mutual sharing of one or more electrons
Metallic bonding – type of chemical bond that holds the atoms together in a solid metal. It’s the attraction between the sea of electrons and the positive metal ions. (more important for pure chem.)
Covalent compounds
- simple molecular compounds like hydrogen molecule, water molecule etc.
- giant molecular structure like diamonds and silicon dioxide (pure)
- graphite
Ionic compounds – self explanatory
Metallic substances – pure metals and alloys
Types of substances
Simple molecular
Types of bonds broken during change of state: Intermolecular forces of attraction.
Strength of the bond broken:Weak
Melting point and Boiling point:Low
Giant molecular or Giant Covalent
Types of bonds broken during change of state:Covalent
Strength of the bond broken:Strong
Melting point and Boiling point:High
Ionic Compounds
Types of bonds broken during change of state:Ionic Bonds
Strength of the bond broken:Strong
Melting point and Boiling point:High
Metals Types of bonds broken during change of state:Metallic Bonds
Strength of the bond broken:Strong
Melting point and Boiling point:High
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Atomic Structure Again
Atomic Structure
Particle
Proton
Relative mass 1
Relative Charge +1
Neutron
Relative mass 1
Relative Charge 0
Electron
Relative mass 1/2000 or appro = 0 or 1/1840
Relative Charge -1
Proton number = Number of protons or neutrons in an atom
Nucleon number = sum of number of neutrons and protons in an atom. (Note this is not the same as relative atomic mass although in our syllabus it is the same for most atoms)
Isotopes are atoms of the same element having the same atomic number but different number of neutrons
Remember anything more than proton number 20, you CANNOT draw the electronic configuration. If the questions or number of valence electrons, LOOK AT GROUP NUMBER!!
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Entry by
Json Lim
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Particle
Proton
Relative mass 1
Relative Charge +1
Neutron
Relative mass 1
Relative Charge 0
Electron
Relative mass 1/2000 or appro = 0 or 1/1840
Relative Charge -1
Proton number = Number of protons or neutrons in an atom
Nucleon number = sum of number of neutrons and protons in an atom. (Note this is not the same as relative atomic mass although in our syllabus it is the same for most atoms)
Isotopes are atoms of the same element having the same atomic number but different number of neutrons
Remember anything more than proton number 20, you CANNOT draw the electronic configuration. If the questions or number of valence electrons, LOOK AT GROUP NUMBER!!
Enjoy!
Entry by
Json Lim
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Test For Gases
Test for gases
Gases
Ammonia
Colorless, pungent
Turns Red litmus blue
Carbon dioxide
Colorless, Odourless
Gives a white ppt with limewater
Chlorine
Greenish Yellow, pungent
Turns Blue litmus red and then bleaches red litmus
Hydrogen
Colorless, Odourless
Extinguish lighted splint with a pop sound
Oxygen
Colorless, Odourless
Relights glowing splint
Sulphur dioxide
Colorless, Choking
Turns acidified potassium dichromate from orange to green
Nitrogen dioxide
Reddish Brown, pungent
Turns Blue litmus red
Water
Colorless Odourless
Condenses into cold water. Turns White anhydrous copper sulphate turns blue,
Cobalt chloride paper turns blue to pink
Enjoy!
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Json Lim
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Gases
Ammonia
Colorless, pungent
Turns Red litmus blue
Carbon dioxide
Colorless, Odourless
Gives a white ppt with limewater
Chlorine
Greenish Yellow, pungent
Turns Blue litmus red and then bleaches red litmus
Hydrogen
Colorless, Odourless
Extinguish lighted splint with a pop sound
Oxygen
Colorless, Odourless
Relights glowing splint
Sulphur dioxide
Colorless, Choking
Turns acidified potassium dichromate from orange to green
Nitrogen dioxide
Reddish Brown, pungent
Turns Blue litmus red
Water
Colorless Odourless
Condenses into cold water. Turns White anhydrous copper sulphate turns blue,
Cobalt chloride paper turns blue to pink
Enjoy!
Entry by
Json Lim
http://www.oleveltuition.com/
Purification
Note: Methods of purification are used only on mixtures. You cannot separate hydrogen from water using these methods.
Separation Techniques
Method
Filtration
Remove insoluble substances from liquids
Distillation
Obtain solvent from solute (water from salt water)
Fractional Distillation
Separate a mixture of miscible liquids (petroleum, ethanol and water)
Separating funnel
Separate a mixture of immiscible liquids (oil and water)
Crystallization
Obtain solute from solution (sugar from sugar solution, salts from their own salt solution)
Chromatography
Separate mixtures that contain chemically similar components. Very often used for identification
Crystallization (important for salt making)
Steps to take
• Heat the solution to obtain a saturated solution
• Once saturated, allow the solution to cool
• Crystals of the salt will appear
• Filter the crystals from the solution
• Dry the salt between filter paper
Chromatography (Pure Chemistry only)
• Rf value = distance moved by the spot/distance move by the solvent front. Rf value cannot be more than 1.
Test for purity
• Test for constant melting and boiling point
• Chromatography
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Entry by
Json Lim
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Separation Techniques
Method
Filtration
Remove insoluble substances from liquids
Distillation
Obtain solvent from solute (water from salt water)
Fractional Distillation
Separate a mixture of miscible liquids (petroleum, ethanol and water)
Separating funnel
Separate a mixture of immiscible liquids (oil and water)
Crystallization
Obtain solute from solution (sugar from sugar solution, salts from their own salt solution)
Chromatography
Separate mixtures that contain chemically similar components. Very often used for identification
Crystallization (important for salt making)
Steps to take
• Heat the solution to obtain a saturated solution
• Once saturated, allow the solution to cool
• Crystals of the salt will appear
• Filter the crystals from the solution
• Dry the salt between filter paper
Chromatography (Pure Chemistry only)
• Rf value = distance moved by the spot/distance move by the solvent front. Rf value cannot be more than 1.
Test for purity
• Test for constant melting and boiling point
• Chromatography
Enjoy!
Entry by
Json Lim
http://www.oleveltuition.com/
Equipment to measure volumes
Measurement Equipment
Apparatus
Stopwatches
Seconds, time
Thermometer
Degrees Celsius, temperature
Beaker
Cm3, rough volume up to 250.
Measuring cylinder
Cm3, volume nearest to Cm3
Pipette
Cm3, fixed volume of 5, 10, 20, 25, 50 Cm3
Burette
Cm3, volume nearest o.1 Cm3
Gas syringe
Cm3, volume of gas
Enjoy!
Entry by
Json Lim
http://www.oleveltuition.com/
Apparatus
Stopwatches
Seconds, time
Thermometer
Degrees Celsius, temperature
Beaker
Cm3, rough volume up to 250.
Measuring cylinder
Cm3, volume nearest to Cm3
Pipette
Cm3, fixed volume of 5, 10, 20, 25, 50 Cm3
Burette
Cm3, volume nearest o.1 Cm3
Gas syringe
Cm3, volume of gas
Enjoy!
Entry by
Json Lim
http://www.oleveltuition.com/
Terms used in Science Examinations
Terms used in Science Examinations
• Define: you are only required to write a concise statement to say what something is or means
• State: A short, concise answer is expected without explanation
• Explain: Means some reference to Chemical theory
• Describe: You are to state the main points in words (sometimes with diagram, if appropriate)
• Discuss: You are to give a critical account of the points in a topic
• Predict or Deduce: You are to deduce an answer from information in the question or from earlier answers (you are not expected to produce answer from memory)
• Suggest: You are not expected to know the correct answer. You are to make a logical deduction from the information given in the question or passage.
• Comment: Give points of interest which are relevant to the question. There can be many answers and the number points you give depends on the marks for the question.
• Find: Normally calculate, measure etc
• Determine: answers normally obtained by calculations or reading of a graph
• Estimate: obtain an answer as accurately as possible.
• Construct: Normally applies to the construct of the chemical equations
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Entry by
Json Lim
http://www.oleveltuition.com/
• Define: you are only required to write a concise statement to say what something is or means
• State: A short, concise answer is expected without explanation
• Explain: Means some reference to Chemical theory
• Describe: You are to state the main points in words (sometimes with diagram, if appropriate)
• Discuss: You are to give a critical account of the points in a topic
• Predict or Deduce: You are to deduce an answer from information in the question or from earlier answers (you are not expected to produce answer from memory)
• Suggest: You are not expected to know the correct answer. You are to make a logical deduction from the information given in the question or passage.
• Comment: Give points of interest which are relevant to the question. There can be many answers and the number points you give depends on the marks for the question.
• Find: Normally calculate, measure etc
• Determine: answers normally obtained by calculations or reading of a graph
• Estimate: obtain an answer as accurately as possible.
• Construct: Normally applies to the construct of the chemical equations
Enjoy!
Entry by
Json Lim
http://www.oleveltuition.com/
Tuesday, September 22, 2009
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