chemistrychpter5,6&7

7/30/2019 ChemistryChpter5,6&7.

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Chapter 5 : Chemical Bonds ionic bonds ( metal + non metal ) transfer electron

covalent bonds ( non metal + non metal )

sharing electron

Formation of Compounds

Different elements that chemically bonded together

Octet electron arrangement 8 valence electrons

Duplet electron arrangement 2 valence electrons

Eg : Compound water is hydrogen & oxygen atoms are chemically bonded together

Stability of Noble Gases

Not gain, lose nor share electrons with other atoms.

Do not combine with atoms of other elements

Chemically unreactive.

Exist as monoatomic.

Ionic Bonds

Formed = transfer of electrons from metal atoms to non-metal atoms Metal atoms donate valence electrons to form positive ions (cations, Mb

Non-metal atoms receive electrons to form negative ions (anions, Xa-) Cations & anions are attracted to each other by strong electrostatic force of

attraction

Formula of an Ionic Compound


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Cation Mb+

Anion Xa-

Formula formed = MaXb

Structure of ionic compounds

The oppositely-charged ions are attracted to each other by a strongelectrostatic force.

It form a rigid 3-D lattice structure Formed crystal. Giant ionic lattice.

Covalent Bonds

Formed from the sharing of valence electrons between non-metal atoms Each shared pair of electrons is as 1 covalent bond. It produces molecules. Form between non-metal atoms from Group 15, 16 & 17 and sometimes can be

formed from Group 14 (carbon and silicon) & hydrogen. Covalent bond can be formed from atoms of the same element and atoms of

different elements.

Types of covalent bond formed

Single bond = one pair of electrons shared between two atoms.Double bond = two pair of electrons shared between two atoms.Triple bond = three pair of electrons shared between two atoms.

Formula of a Covalent Compound

Non-metal X atom (valence electron is a)Combine with non-metal Y atom (valence electron is b)b = simplest ratio (n) and a = simplest ratio (m)Formula of a covalent compound formed, XnYm

Structure of covalent compounds


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Simple molecular structure/giant molecular structure. The atoms of the molecules are joined together by strong covalent bond Intermolecular forces are weak by weak van der Waals forces.

Properties of Ionic and Covalent Compounds

Ionic Compound

Ionic bonding is strong electrostatics forces between the oppositely-charged ions

Covalent Compound

Covalent bonding is strong bonding between the atoms in the molecule

Ionic Compound Differences Covalent Compound

Ions Particles Molecules

Lost/gained Electron Shared

Strong electrostatics forces(Ionic) between oppositely-charged ions arranged in a 3-D giant crystal lattice

Forces Strong (Covalent) between atoms inthe molecule. Weak forces ofattraction between the molecules (vander Waals forces)

Solid State Gases/volatile liquids

High Melting point Low (simple) High (giant)High Melting point Low (simple) High (giant)

Non-volatile Volatility Very volatile (simple)Non-volatile (giant)

Dissolve in water & polarsolvents

Solubility in water Do not dissolve in water

Do not dissolve Solubility in organic

solvent

Dissolve

Conduct electricity in liquid &

aq solution(positive &

negative ions move freely).

Cannot conduct electricity in

solid(fixed & cannot move

freely).

Electricity

conductor

Cannot conduct electricity in any state

(no free mobile ions)

Uses of covalent compounds as solvent

o Ether solvents in the extraction of chemicals from aqueous solution


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o Alcohol solvents used to make ink and dye because these solvent are volatileo Turpentine dissolved painto CFC (chlorofluocarbons) solvents to clean computer circuits boardo Propanone remove nail varnish

Chapter 6 Electrochemistry

Electrolyte

Substances that can conduct electricity in molten/aqueous state. Can conduct electricity due to the presence of free moving ions. Example for electrolytes (alkalis, acids, salt solution or molten salt):

molten lead(II) chloride copper(II) sulphate solution

solution containing ions such as hydrochloride acid

Non-electrolyte

Molecules that cannot conduct electricity & will not undergo any chemicalchanges.

It cannot conduct electricity due to the absent of free moving ions. Example of non-electrolytes (covalent substances):

molten acetone

molten naphthalene glucose solution

Conductor

Substances that can conduct electricity in solid/molten state but do not undergoany chemical changes.

It can conduct electricity due to the flow of electrons. Example of conductor:

iron graphite mercury

Ionic Compounds

Solid state Molten/aqueous state (dissolved in water)

Do not conduct electricity Can conduct electricity


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Ions are held in a lattice -

Ions do not move freely Ions are free to move

Covalent Compounds

Solid state Molten/aqueous state (dissolved in water)Do not conduct electricity Do not conduct electricity

Exist in molecules Exist in molecules

Molecules do not have free moving ions Exception: HCl and NH3 exist as free movingions in water

Electrolysis of Molten Compounds

Electrolysis (with battery/electricity current) is a process of decomposition /

breaking down /separation of a compound (electrolyte) into its constituent

elements when electric current passes through it.

Anode Electrode connected to the positive terminal (+) of a battery

Cathode Electrode connected to the negative terminal (-) of a battery

Anion Negatively-charged ion. Example: Cl-, SO42- and O2-

Cation Positively-charged ion. Example: Na+, Zn2+ and Al3+

Classification of electrodes

Inert electrodes Electrodes that do not take part in chemicalreactions during electrolysis

Carbon or platinum

Active electrodes Electrodes that take part in chemical reactions

during electrolysis

Copper or zinc


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Electrolysis of Aqueous Compounds

3 important factors to determine the types of ions to be discharged at theelectrodes : Positions of ions in the electrochemical series Concentration of ions in the solution

Types of electrodes used

1. Positions of ions in the electrochemical series The lower the position of the ion in the electrochemical series, the easier the

ion is selectively discharged.

Electrochemical series

Cation (+) Anion (-)

K+ F-

Na+ SO42-

Ca2+ NO3-

Mg2+ Cl-

Al3+ Br-

Zn2+ I-

Fe2+ OH-

Sn2+

Pb2+

H+

Cu2+


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Ag+

2. Effect of concentration of ions in the solution

The concentration of a particular type of ion is high = ion more likely to be

discharged in electrolysis.

3. Types of electrodes used in the electrolysis

There are 2 important notes:

Inert electrodes: Carbon and platinum (Both of these electrodes do not

react with the electrolytes or products of electrolysis)

Active electrodes: Silver, copper and nickel (Active anode ionises and

concentration of cations in the electrolyte does not change)

Products of Electrolysis of Aqueous Solutions

1. Main factor: Position of ions in the electrochemical series

Cation: The higher the position in the electrochemical series are very stable.

Example: K+ & Na+ are never discharged in an aqueous solution in electrolysis.

Anions: The higher the position in the electrochemical series are very stable.

Example: F - & SO42- are never discharged in an aqueous solution in electrolysis.

2. Second factor: Concentration of the electrolyte

3. Third factor: Types of electrode as anode

Electrolysis in Industries


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A. Extraction of reactive metals

Reactive metals: Sodium, calcium, magnesium & aluminium extract from theircompounds

Example: Extraction of aluminium from aluminium oxide, Al2O3 (bauxite) by usingcryolite, Na3AlF6 at 980C.

B. Purification of metals

Anode: impure metal / Cathode: pure metal Electrolyte: solution containing the ions of the metal to be purified Example: purification of impure copper metal.

C. Electroplating of metals

Electroplating = process of coating the surface of metal objects with a thin &even layer of another metal.

Importance of electroplating is to prevent corrosion & improve the appearance. Cathode: object to be electroplated Anode: pure plating metal Electrolyte: aqueous solution contains plating metal ions

Voltaic Cell/Galvanic cell

Converts chemical energy > electrical energy (-) terminal: more electropositive (higher position in the electrochemical series) (+) terminal: less electropositive (lower position in the electrochemical series) Electrons released (more electropositive metal) through the wire to a less

electropositive metal.

Daniell Cell

It is another example of a voltaic cell. Solutions are connected by a salt bridge (inert electrolyte) or a porous pot.

The main function of a salt bridge/porous pot is to complete the circuit byallowing the movement of ions & prevent two solution from mixing.


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Comparison of Electrolytic Cells and Voltaic Cells

Similarities

o Two electrodes involves in the reactiono Electrons flow through the external circuit (connecting wires)o Anode (oxidation): loss of electronso Cathode (reduction): gain of electrons

Differences

Electrolytic Cell Voltaic Cell

Main basic structuresA battery is needed tosupply electrical energy

Battery is not needed.

Energy conversionElectrical energy >chemical energy

Chemical energy >electrical energy

Transfer of electrons at thepositive terminal

Anode (+ terminal):Oxidation anions loseelectrons at the anode

Cathode (+ terminal):Reduction

Transfer of electrons at the

negative terminal

Cathode (- terminal):Reduction cations accept

electrons from the cathode

Anode (- terminal): Oxidation

Electrochemistry

It is an arrangement of elements according to their tendencies to donateelectrons to form cations.

Higher position = a metal that has a higher tendencies to ionise & form (+) ions.


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Constructed by the potential difference (voltage difference) between pairs ofmetals & the ability of a metal to displace another metal from its own saltsolution.

A) Electrochemical Series based on the Potential Difference (Voltage Difference)

To construct an electrochemical series = measure the potentialdifference between two metals in voltaic cells.

(-) terminal in voltaic cell has a higher tendency to release electrons = higherposition in the electrochemical series

(+ terminal ) in voltaic cell has a lower tendency to release electrons = lowerposition in the electrochemical series.

The greater the potential difference (voltage) = further apart the positions oftwo metals in electrochemical series.

B) Electrochemical Series from the Displacement Reaction of Metals

To construct an electrochemical series = ability of a metal to displace anothermetal from its salt solution.

Higher position of a metal in the electrochemical series = able to displace ametal below it from its salt solution.

The Importance of Electrochemical Series

Terminal of a voltaic cell Voltage produced by a pair of metals Ability of a metal to displace another metal from its salt solution

Metal displacement of hydrogen from an acid

The Importance of Electrochemical Industries

Extract useful metals (Al, Na & Mg) from its ore using electrolysis. Manufacture of useful chemical substances (Cl and NaOH) using electrolysis. Electroplating of Pb with chromium to protect the iron layer. Silver - plating to make fine cutleries. Voltaic cell (batteries)


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Effect of Electrochemical Industries towards the Environment

Heavy metals (chromium and mercury) cause water pollution. Chlorine gas/toxic gas cause problem (irritates) to human respiratory system. Mercury cell (batteries) is highly toxic. Improper disposal of industrial waste cause water pollution.

Chapter 7 Acid and Bases

Acids

Chemical substance which ionises in H2O to produce hydrogen ions, H+. H+(aq) + H2O(l) > H3O

+(aq) Example: HCl(g) + H2O(l) > H3O

+(aq) + Cl -(aq)

Acid Acid name IonsHCl Hydrochloric acid H+, Cl -

HNO3 Nitric acid H+, NO3-

H2SO4 Sulphuric acid H+, SO4

2-

CH3COOH Ethanoic acid H+, CH3COO -

Monoprotic acid = Produce only 1 hydrogen ion per molecule in water. (Eg: HCl) Diprotic acid = Produce 2 hydrogen ions per molecule in water. (Eg: H2SO4) Triprotic acid = Produce 3 hydrogen ions per molecule in water. (Eg: H3PO4)

Bases/Alkalis

Chemical substance which reacts with an acid to produce a salt & water only. Base(s) + acid(aq) > salt + water (l). Example: NaOH(s) + HCl(aq) > NaCl(aq) + H2O(l)

Base Formula Solubility in water Ions (aq)Copper(II) oxide CuO Insoluble base -

Lead(II) oxide PbO Insoluble base -

Magnesium oxide MgO Insoluble base -Zinc hydroxide Zn(OH)2 Insoluble base -


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Aluminium hydroxide Al(OH)3 Insoluble base -

Sodium oxide Na2O Soluble base (alkali) Na+, O2-

Calcium oxide CaO Soluble base (alkali) Ca2+, O2-

Sodium hydroxide NaOH Soluble base (alkali) Na+, OH-

Potassium hydroxide KOH Soluble base (alkali) K+, OH-

Barium hydroxide Ba(OH)2 Soluble base (alkali) Ba2+

, OH-

The Uses of Acids in Our Daily Life

Benzoic acid Its salt are used to preserve food

Carbonic acid To make carbonated drinks

Ethanoic acid A main compound of vinegarHydrochloricacid

To clean metals before electroplating /household cleaning / leather processing/ swimming pool maintenance

Nitric acid Production of fertilisers, explosives,etching and dissolution of metals(purification and extraction of gold)

Sulphuric acid To make detergent, polymer andfertilisers.

Tartaric acid Manufacturing of soft drinks, providetartness to food, as an emetic (asubstance to induce vomiting)

The Uses of Bases in Our Daily Life

Ammonia Production of fertilisers (ammonium and nitrate salts), used inthe manufacture of nitric acid, neutralise the acid (in thepetroleum industry) and prevent premature coagulation in natural/ synthetic latex.

Aluminium hydroxide Manufacture other aluminium compound and to make gastricmedicine (antacid)

Calcium hydroxide To make cement, limewater, neutralise the acidity of soil andapplication of sewage treatment.

Sodium hydroxide Used in the manufacturing of soaps, detergents, and cleaners.

Magnesium hydroxide Suspension of magnesium hydroxide in water are used as anantacid, used as an antiperspirant armpit deodorant and as anon-hazardous alkali to neutralise acidic wastewater.

Chemical Properties


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Monoprotic acid (monobasic acid) is an acid which produce 1 mole of H+ ion when 1

mole of the acid ionise in water.

Diprotic acid (dibasic acid) is an acid which produce 2 moles of H + ions from 1 mole

of the acid in water.

Diprotic acid Diprotic acid nameH2SO4 Sulphuric acid

H2CO3 Carbonic acid

H2CrO4 Chromic acid

H2C2O4 Ethanedioic acid / Oxalate acid

Triprotic acid (tribasic acid) is an acid which produce 3 moles of H+ ions from 1

mole of the acid in water.

Triprotic acid Triprotic acid nameH3PO4 Phosphoric acid

Acid AlkaliIn water, an acid will ionise to formhydrogen ion, H+.

In water, an alkali will ionise to formhydroxide ion, OH -.

Sour Bitter < than 7 > than 7

Blue to red Red to Blue

Universal indicator (Orange & red) Universal indicator (Blue & purple)

Methyl orange (Red) Methyl orange (Yellow)

React with bases to produce saltsand water.2HCl(aq) + CuO(s) > CuCl2(aq) +H2O(l)

React with acids to produce saltsand water.NaOH(aq) + HCl(aq) > NaCl(aq) + H2O(l)

React with metals (reactive metal, higherposition than H+ in the electrochemical

series) to produce salts and hydrogengas.2HCl(aq) + Zn(s) > ZnCl2(aq) + H2(g)

React with an ammonium salt (alkali isheated) to produce ammonia gas.

Ba(OH)2(aq) + 2NH4Cl(s) > BaCl2(aq) +2H2O(l) + 2NH3(g)

React with carbonates to producesalts, carbon dioxide gas and water.H2SO4(aq) + ZnCO3(s) > ZnSO4(aq) +H2O(l) + CO2(g)

React with aqueous salt solutions toproduce metal hydroxides (as precipitate).2NaOH(aq) + CuSO4(aq) > Na2SO4(aq) +Cu(OH)2(s)

Monoprotic acid Monoprotic acid name

HCl Hydrochloric acid

HNO3 Nitric acid

CH3COOH Ethanoic acid


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C6H8O7 Citric acid

The pH scale & the Measurement of pH Value of a Solution

pH scale = Number to represent the degree of acidity/alkalinity of a solution. pH = Measurement of the concentration of hydrogen ions (H+) in the solution. Alkaline = The lower the concentration of the H+ ions, the higher the pH value.

= pH value ( >7 ) Acidic = The higher the concentration of the H+ ions, the lower the pH value.

= pH value (


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Strength of an acid the degree of ionisation of the acid in water. Strong acid an acid which ionises completely in water to form high

concentration of hydrogen ions (H+). Example of strong acid: Mineral acid hydrochloric acid (HCl), nitric acid

(HNO3) and sulphuric acid (H2SO4). Example of the strong acid reaction in water: HCl(aq) > H+(aq) + Cl-(aq) (The

concentration of hydrogen ions is [=] to the concentration of hydrochloric acid)

Weak Acids

Weak acid an acid which ionises partially in water to form low concentrationof hydrogen ions (H+).

Example of weak acid: ethanoic acid (CH3COOH) & methanoic acid (HCOOH) Example of the weak acid reaction in water: CH3COOH CH3COO

-(aq) + H+

(aq) {The concentration of hydrogen ions is low & the ions (CH3COO- and H+)

reacts to reform the ethanoic acid molecule = reversible reaction}

Strong Alkalis

Strength of alkali the degree of ionisation of the alkali in water. Strong alkali an alkali which ionises completely in water to form high

concentration of hydroxide ions (OH ). Eg of strong alkali: Sodium hydroxide (NaOH) solution, potassium hydroxide

(KOH) solution & barium hydroxide [Ba(OH)2] solution.

Eg of the strong alkali reaction in water: NaOH(aq) > Na+(aq) + OH-(aq)

Weak Alkalis

Weak alkali an alkali which ionises partially in water to form lowconcentration of hydroxide ions (OH ).

Example of weak alkali: ammonia (NH3) solution.

Eg of the weak alkali reaction in water: NH3(g) + H2O(l) NH4+

(aq) + OH-

(aq)


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Concentration of Acids and Alkalis

Quantity of solute = grams [ g dm-3 ] or moles [ mol dm-3]. Concentration (g dm-3) = mass of solute (g) / volume of solution (dm3) Concentration (mol dm-3) = no of moles of solute (mol) / volume of solution (dm3)

Relationship between No of Moles with Molarity & Volume of a Solution

o Molarity (mol dm-3) = no of moles of solution (mol) / volume of solution (dm3)o M = molarity of solution (mol dm-3), V = Volume of solution (dm3), n = Number of

moles of solute (mol)o

M = n/V

Preparation of Standard Solutions

Standard solution = a solution in which its concentration is accurately known . Prepared by using volumetric flask with a fixed volume (100 cm3, 200 cm3, 250

cm3, 500 cm3 and 1000 cm3)

Preparation of a Solution by Dilution Method

Dilution = a process of diluting a concentrated solution by adding asolvent (water) to obtain a more diluted solution.

The concentration of the solution decreases after dilution. The no of moles of solute in the solution remains unchanged after dilution. (MaVa) / 1000 = (MbVb) / 1000 Ma = Initial molarity of solution, Mb = Final molarity of solution, Va = Initial

volume of solution and Vb = Final volume of solution


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Relationship between pH Values and Molarities of Acids/Alkalis

pH values depends on degree of dissociation and molarity/concentrationof hydrogen ions, H+/ hydroxide ions, OH- in the solution.

The higher the molarity of a strong acid, the lower is its pH value.

The higher the molarity of a strong alkali, the higher is its pH value. The molarity of an acid can be changed when (i) water is added, (ii) an

acid of different concentration is added and (iii) an alkali is added.

Neutralisation

Neutralisation = a reaction between an acid & a base/alkali toproduce salt and water only.

Acid + alkali > salt + water Ionic equation of neutralisation: H+(aq) + OH-(aq) > H2O(l)

Application of Neutralisation Reactions in Daily Life

Digestive juicesin stomach

Break up food (only in acidic condition) &maintained at pH of between 1 & 2

Insect stings Bees & ants inject an acidic liquid into the skinbut wasps inject an alkaline liquid.

Toothpaste An alkaline compound (magnesium hydroxide)in toothpastes neutralises the organicacids produced by the food.

pH of the

swimming pool

Calcium hypochlorite, Ca(OCl)2 is added to thewater.

Latex industries Ammonia is used to neutralise the organic acidproduces by bacteria to prevent coagulation.

Neutralisation Manufacture fertilisers, soaps and detergentsEffluent from It can be treated with lime.


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factories

Sulphuric acid Manufacture of dyes, explosives, steel,fertilisers, paints and plastics.

Soil treatment Plants grow best when the pH of the soil isabout 7. The soil is too acidic, quick lime

(calcium oxide) or slaked lime (calciumhydroxide) is added to the soil to neutralise theexcess acid.

Acid-base Titration

Titration a quantitative analysis method to determine the volume of

an acid that is required to neutralise a fixed volume of an alkali / a quantitative

analysis method to determine the volume of an alkali that is required to

neutralise a fixed volume of an acid.

End point of a titration a point which neutralisation occurs when the acid

has completely neutralised the alkali / the alkali has completely neutralised the

acid.

Reactants: Acid and alkali

Products: Salt and water

End point can be determined by (i) the use of acid-base indicators duringtitration, (ii) measuring the pH values of the solution during titration and (iii)

measuring the electrical conductivity of solution during titration.

Indicator Alkali Neutral Acid

Litmus Blue Orange Red

Methyl orange Yellow Orange Red

Phenolphthalein Pink Colourless Colourless

chemistrychpter5,6&7

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