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Chemical Reactions and Equations
In a chemical reaction, at least one of the following will occur: Change in state Change in colour Evolution of a gas Change in temperature Formation of a precipitate A chemical equation is the symbolic representation of a chemical reaction in the form of chemical formulae, signs, symbols, and directions. In which the reactant entities are given on the left-hand side and the product entities on the right-hand side. Balanced chemical equation Reactants → Products LHS RHS Total number of atoms on the LHS = Total number of atoms on the RHS How to balance an equation Write reactants and products Balance the maximum number of a particular atom on both sides Balance other atoms A complete balanced equation should look like CO g + 2H2 g →340 atm CH3OH l Types of reactions Combination reaction o Two or more reactants combine to form one single product. Examples: CaO s + H2O l → Ca(OH)2 aqCalcium oxide Water Calcium hydroxid e (Quick lime) (Slaked lime) C s + O2 g → CO2 gCarbon Oxygen Ca rbon dioxide 2H2 g + O2 g → 2H2O lHydrogen Oxygen Water Exothermic reaction – Heat gets released in the reaction. Most combination reactions are exothermic. For example,
Endothermic reaction – Heat is absorbed in the reaction. Very few combination reactions are endothermic. For example, 12N2 g + O2 g → NO2 g Decomposition reaction o A single reactant breaks into several simple products. Examples: 2FeSO 4 Ferrous sulphate→ Δ Fe 2 O 3 Ferric oxide+SO 2 +SO 3 CaCO 3 Limestone → Δ CaOCalcium oxide+ CO 2 2AgClSilver chloride→ Δ 2AgSilver+Cl 2 o All decomposition reactions are endothermic [they absorb heat ]. Displacement reactions: o In displacement reactions, a more reactive metal can displace a less reactive metal from their compounds in aqueous solutions. (However, a less reactive metal cannot displace a more reactive metal.) Example: CuSO4 + Zn → ZnSO4 + Cu Copper Sulphate Zinc Zinc Sulph ate Copper (Blue) (Colourless) (Red) Fe s + CuSO4 aq → Cu s + FeSO4 aqIron Copper sulphate Copper Iron sulphat e Double displacement reaction o Exchange of ions occurs between two compounds. Example; Na2SO4 aq + BaCl2 s → BaSO4 aq + 2NaCl sSodium sulphate Barium chlori de Barium sulphate Sodium chloride When the aqueous solution of two compounds react by exchanging their respective ions, such that one of the products formed is insoluble salt and appears in the form of a precipitate, then the reaction is said to be precipitation reaction. When an acid solution reacts with a base and the two exchange their respective ions, such that only salt and water are products, then the reaction is called neutralisation reaction. When two compounds react with each other and displace their ions, in such a manner that one of the product formed either decomposes into gaseous compounds or is formed in gaseous state, then the reaction is called gas-forming reaction. Oxidation → When a substance gains oxygen or loses hydrogen Oxidation in everyday life
Acids, Bases and Salts
Acid : Turns blue litmus colour to red Bas e: Turns red litmus colour to blue Bases which are soluble in water are called alkalis. Example KOH, Mg(OH) 2 Turmeric is a natural indicator Reaction of acid with metals In most cases, metals replace hydrogen from acids. Metal oxide + Acid Metal oxide + Acid → Salt + Water Reaction of base with metals 2NaOH + Zn →Na 2 ZnO 2 (sodium zincate) + H 2 Acids with metal carbonate and hydrogen carbonate Carbonate + Acid → Salt + Water + CO 2 Further on passing the carbon dioxide gas evolved through lime water. Ca(OH) 2 + CO 2 → CaCO 3 + H 2 O Acid – Base reaction Acid + Base → Salt + Water In water solution Acid → H+^ ion ; H+^ + H 2 O → H 3 O+ Base → OH–^ ion Higher H+^ concentration → Strong acid Lower H+^ concentration →Weak acid Higher the OH–^ concentration → Stronger the base pH Measure pH → Measure of acidity →Measure H+^ concentration on the scale (0 – 14)
pH 7 → Neutral solution pH < 7 → Acidic solution pH > 7 → Basic solution Salts’ pH = 7 Human body pH = 7.0 – 7. Change in pH in body causes → Tooth decay, stomach pain, burning pain (Honey bee sting) Plants and animals are sensitive to pH change Self defence by animals and plants through chemical wefare Common salt → NaCl Bleaching powder → CaOCl 2 Preparation – Ca(OH) 2 + Cl 2 →CaOCl 2 + H 2 O Use – Oxidising agent
Metals and Non-metals
Metals Physical properties Shining surface (in pure state) [called metallic lustre] Generally hard [varies from metal to metal] Malleable [i.e. can be made thin sheets by beating] Ductile [i.e. can be drawn into thin wires] o [Gold → Highly ductile] Good conductors of heat High melting point Conduct electricity Produce sound [some metals; these are called sonorous] Non-metals Non-metals are found in all the three states i.e. solid, liquid and gas, at room temperature. Iodine (non-metal) has lustre Carbon has allotropes (exists in different forms) o Diamond is hard o Graphite (Conducts electricity) Metals Non-metals
- Generally, these are hard and lustrous. These are soft and have no lustre.
- These are malleable and ductile (Malleable: can be beaten into sheets; Ductile: can be drawn into wires). These are non-malleable and non- ductile.
- These are sonorous (produce ringing sound when struck). These are not sonorous.
- These are good conductors of heat and electricity. These are poor conductors of heat and electricity. Chemical properties: Metals Non-metals These react with oxygen to produce metal oxides, which are basic in nature. These react with oxygen to form non- metallic oxides, which are acidic in nature.
Chemical properties Reaction with oxygen Combine with oxygen to form oxides 2Cu + O 2 → 2CuO 4Al + 3O 2 → 2Al 2 O 3 Most metal oxides are insoluble in water. If soluble, they form alkali. Na 2 O + H 2 O → 2NaOH K 2 O + H 2 O → 2KOH Sodium, potassium react very easily with O 2. So, they are kept immersed in kerosene. Mg, Al, Zn, Pb form thin layers of oxides. Reaction with water Produce metal oxide + H 2 If oxide is soluble, then metal hydroxide is formed. Mg → Doesn’t react with cold H 2 O Al, Zn, Fe do not react with H 2 O, but react with steam. 2Al + 3H 2 O → Al 2 O 3 + 3H 2 3Fe + 4H 2 O → Fe 3 O 4 + 4H 2 Chemical properties: Metals Non-metals These react with acids to produce metal salts and hydrogen gas. These do not react with acids. Some metals react with bases to produce hydrogen gas. Reactions of non-metals with bases are complex. Reaction with Acids Metal + Dilute acid → Metal salt + H 2 H 2 doesn’t evolve in the case of HNO 3 as it is a strong oxidising agent. It oxidises H 2. Cu does not react with acids like dilute H 2 SO 4 and dilute HCl. Aqua regia o Freshly-prepared concentrated HCl and concentrated HNO 3 in 3:1 ratio
o Metals at the top have greater reducing power. This power decreases on moving down the series. o Metals at the top show greater tendency to get oxidised. o Metals above hydrogen in the reactivity series liberate hydrogen gas from mineral acids. o Metals at the top displace metals lower in the series from the aqueous solution of their salts. o Metal oxides above Al, cannot be reduced by common reducing agents, the reverse is true for metal oxides below Al. K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au Metals + Non-metals o 1) o 2) Physical Properties of Ionic compounds
- Solid
- Hard [because of strong attraction force]
- Brittle
- High melting and boiling points
- Soluble in H 2 O; insoluble in kerosene, petrol
- Conduct electricity in H 2 O solution Metals + Non-metals o 1)
o 2) Physical Properties of Ionic compounds
- Solid
- Hard [because of strong attraction force]
- Brittle
- High melting and boiling points
- Soluble in H 2 O; insoluble in kerosene, petrol
- Conduct electricity in H 2 O solution Elements on earth are found in different parts of earth and are found in different forms. Different parts of earth include lithosphere, hydrosphere and atmosphere. Elements or compounds, which occur naturally in the Earth’s crust, are known as minerals. Extraction of metals Low active metals Middle active metals Roasting – Heating of sulphide ore in excess air
Carbon and its Compounds
Covalent bonds The bonds formed by the sharing of electrons are known as covalent bonds. In covalent bonding, both the atoms (that are participating in the bonding) share electrons, i.e., the shared electrons belong to both the atoms. Carbon contains four electrons in its valence shell. It always forms covalent bonds as it is difficult for it to lose or gain four electrons in order to complete its octet. Allotropes of Carbon o Allotropes have different appearances and physical properties, but chemically they are the same. o There are three allotropes of carbon: diamond, graphite, and buckminsterfullerene. Diamond Graphite Buckminsterfullerene Amorphous Solid: An amorphous solid is a non-crystalline solid with no well-defined ordered structure. Amorphous forms of carbon are: Charcoal, Lampblack or soot; Coal; Coke Catenation Catenation is the ability of an element to combine with itself through covalent bonds. Carbon shows extensive catenation, giving rise to large number of compounds. It can form strong single, double, and triple bonds with other atoms of carbons. Carbon can combine with itself to form chain, branched, and ring structures. Hydrocarbons The compounds made up of only carbon and hydrogen are called hydrocarbons. The compounds of carbon that contain only single bonds among carbon atoms are called saturated compounds Compounds containing double and triple bonds among carbon atoms are called unsaturated compounds.
If the hydrocarbons are saturated (like methane and ethane), then they are called alkanes; if they are unsaturated, then they are alkenes (containing double bonds) and alkynes (containing triple bonds). Aliphatic compounds o Organic compounds that have a straight chain or branched chain structures. o Example, methane, ethane, propane, 2-methylpropane etc. o They are classified as: Alkanes (contain only single bonds): General molecular formula is CnH(2n+2) where, n = number of carbon atoms. Alkenes (contain atleast one double bond): General molecular formula is CnH2n where, n = number of carbon atoms. Alkynes (contains atleast one triple bond): General molecular formula is CnH2n- 2 where, n = number of carbon atoms. Alicyclic Saturated Hydrocarbons: o Saturated organic compounds in which carbon atoms form a closed chain. Aromatic Compounds o Organic compounds that contain a ring system and have characteristic odour. o First member is Benzene. Structural Isomerism o Organic compounds which have same chemical formula but differ in their structures are known as isomers and this phenomenon is known as isomerism. o For example, 2-methylpropane is the isomer of n-butane. o Types of structure isomerism: Chain/ skeletal/ nuclear isomerism: difference in the structure of the carbon chain that forms the nucleus of the molecule Position isomerism: difference in the position of the functional group, the carbon‒carbon multiple bonds or the substituent group Functional group isomerism: presence of different functional groups Metamerism: difference in the number of carbon atoms on either side of the functional group Functional groups o Carbon also forms covalent bonds with oxygen, nitrogen, and sulphur atoms. o Presence of any of these elements in a compound confers specific properties to the compound. o A group of atoms that imparts specific properties to hydrocarbons is called a functional group. o Some functional groups in carbon compounds are shown in the given table. Hetero atom Name of functional group Formula of functional group Chlorine/Bromine Halo- (Chloro/Bromo) – Cl, – Br Oxygen Alcohol – OH Aldehyde – CHO Ketone >C=O Carboxylic acid – COOH
- Alcohol Suffix: - ol
- Aldehyde Suffix: - al
- Ketone Suffix: - one
- Carboxylic acid Suffix: - oic acid
- Double bond (alkenes) Suffix: - ene
- Triple bond (alkynes) Suffix: - yne Using the IUPAC of an organic compound, it's structure can be determined. The following rules help in accomplishing the task: Step − I : Identify the root word. It forms the carbon skeleton in the structure. Step − II : Write the number of carbon atoms as per the root word and number them from any end. Step − III : As per the suffix in the name, ascertain the type of bond present in the compound. If any multiple bond is present, place it between the carbon atoms as stated in the IUPAC name. Step − IV : Place the substituents at the carbon atoms mentioned in the IUPAC name. Step − V : Place the functional group at the designated carbon atom.
Step − VI : Complete the valencies of the remaining carbon atoms by attaching hydrogen atoms. Chemical properties of carbon compounds o Combustion reaction : o Carbon burns in air to form carbon dioxide and hydrocarbons burn in air to give carbon dioxide and water. Heat and light are also released in these processes. o Oxidation reaction : Combustion of carbon to form carbon dioxide is an oxidation reaction. When alcohols are oxidised, carboxylic acids are obtained. Addition reaction : o Unsaturated hydrocarbons yield saturated hydrocarbons when reacted with hydrogen in the presence of catalysts. Substitution reaction : o Under specific conditions, hydrogen atoms present in hydrocarbons can be replaced by atoms of other elements like chlorine and bromine. Ethanol (alcohol), CH 3 CH 2 OH: o Liquid at room temperature o It is a good solvent o Soluble in water in all proportions Chemical properties of ethanol
The two ends of molecules of soaps and detergents are different. Their one end is hydrophilic (the cationic part) and the other is hydrophobic (the hydrocarbon chain part). When soap molecules are present in water, the molecules arrange themselves in the form of a cluster called a micelle. Soap does not work properly when water is hard. This is primarily because hard water contains salts of calcium and magnesium. When soap is added to hard water, it reacts with these salts to form an insoluble substance called scum. Advantages of detergents over soaps Detergents clean efficiently in hard water whereas soaps are rendered inactive in hard water. Detergents are more soluble in water than soaps. Detergents have strong cleansing action than that of soaps. Detergents can work well in acidic medium, whereas soaps do not work in acidic medium.
