Magnesium ribbon is cleaned because magnesium react with atmospheric oxygen and CO2 form stable compound. i.e. magnesium oxide & magnesium carbonate which causes hinderance in burning.
2Mg + O2 ----→ 2MgO
Magnesium Oxygen Magnesium oxide
1. Hydrogen + Chlorine → Hydrogen chloride
H2 + Cl2 → 2HCl
2. Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
3BaCl2 + Al2(SO4)3 → 3BaSO4 + 2AlCl3
3. Sodium + Water → Sodium hydroxide + Hydrogen
2Na + 2H2O → 2NaOH + H2
1. Solutions of barium chloride and sodium sulphate in water react to give insoluble barium suphate and the solution of sodium chloride
BaCl2 (aq) + Na2SO4 (aq) → BaSO4 (S) + NaCl (aq)
2. Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solutions and water.
NaOH (aq) + HCl (aq) → NaCl (aq) + H2O
(i) Substance 'X' is calcium oxide commonly known as Quick Lime.
Its formula : CaO
(ii) Calcium oxide reacts with water and form calcium hydroxide or slaked lime.
CaO(s) + H2O(l) → Ca(OH)2 (aq)
Calcium oxide Water Calcium hydroxide
Electrolysis of water is carried out in this activity. In which electric current is passed through water with sulphuric acid.
2H2O(l) → 2H2(g) + O2(g)
The gas collected over cathode is Hydrogen and the gas collected over anode is Oxygen.
Volume of H2 gas is double than that of O2 gas collected over anode. Through a balanced chemical equation, its clear that two molecules of hydrogen and one molecule of oxygen evolved.
Fe (s) + CuSO4 (aq) ----→ FeSO4 (aq) + Cu(s)
Iron Copper Sulphate Ferrous Suplhate Copper
Displacement reaction occurs. As Iron is more reactive than copper, iron displace copper from copper sulphate and forms ferrous sulphate, which is light green colour compared to dark blue colour solution of copper sulphate.
Pb(NO3)2 (aq) + 2KI (aq) → PbI2 (s) + 2KNO3 (aq)
Lead Nitrate Potassium Iodide Lead Iodide Potassium Nitrate
When the aqueous solution of lead Nitrate is mixed with potassium Iodide, we obtain a precipitate of lead iodide and a solution of potassium nitrate. In double ddisplacement reaction their is exchange of ions between the reactant. In this reaction, the cation Pb2+ and K+ exchange their anions NO3- and I- to give new substance PbI2 and KNO3.
(i) 4Na(s) + O2(g) → 2Na2O(s)
In this reaction sodium is oxidised because oxygen combines to sodium form sodium oxide and oxygen is reduced because it is converted into sodium oxide.
(ii) CuO(s) + H2(g) → Cu(s) + H2O(l)
In above reaction, copper oxide is reduced to form copper because copperoxide loses oxygen and form copper where as Hydrogen gets oxidised by gaining oxygen from copper oxide and form water molecule.
Explanation:
(a) Lead is getting reduced is incorrect as lead oxide is getting reduced.
(b) Carbon dioxide is getting oxidised is incorrect answer as carbon is getting oxidised.
(c) Carbon is getting oxidised is correct answer.
(d) Lead oxide is getting reduced is correct answer.
Respiration is a process in which we inhale oxygen from the atmosphere which oxidises glucose in our body to produce carbon dioxide, water and heat is evolved.
C6H12O6(aq) + 6O2(g) ----------> 6CO2 + 6H 2O(l) + Heat
Hence, heat is evolved during respiration it is considered as an exothermic reaction.
In decomposition reaction, a single reactant breaks down into two or more simpler product, while in combination reaction two or more reactant combine to form a single product. Therefore decomposition and combination reaction are opposite.
Example of decomposition :
(i) 2FeSO4(s) --Heat→ Fe2O3(s) + SO2(g) + SO3(g)
Ferrous sulphate Ferric oxide
(ii) CaCO3(s) --Heat→ CaO(s) + Co2(g)
Lime stone Quick lime
Example of combination :
(i) CaO(s) + CO2(g) → CaCO3(s)
Quick lime Carbon dioxide Lime stone
(ii) Burning of coal →
C(s) + O2(g) → CO2(g)
Decompositive reaction in presence of Heat:
2Pb(NO3)2 (s) -- Heat → 2PbO (s) + 4NO2(g) + O2(g)
Lead Nitrate Leadoxide Nitrogen dioxide Oxygen
Decompositive reaction in presence of Light:
2AgCl - Light→ 2Ag + Cl2 gas
Silver Chloride (white) (grey)
Decompositive reaction by the use of electricity:
2H2O (l) -- Electricity→ 2H2 (g) + O2 (g)
water hydrogen gas oxygen gas
Displacement Reaction : In this reaction more reactive element displaces the less reactive element
AB + C → AC + B
eg.:
(i) Fe + CuSO4 → FeSO4 + Cu
(ii) Pb + CuCl2 → PbCl2 + Cu
Double Displacement Reaction : In this reaction exchange of ions takes place
AB + CD → AC + BD
eg.:
(i) Na2SO4 + BaCl2 → 2NaCl + BaSO4
(ii) HCl + AgNO3 → AgCl + HNO3
Reaction occurs as:
2AgNO3 + Cu → Cu(NO3)2 + 2Ag
Silver Copper Copper Silver
nitrate nitrate
In a chemical reaction a insoluble substance (precipitate) is formed is called precipitation reaction.
eg.:
(i) AgNO3 + NaCl → AgCl + NaNO3
Silver Sodium Silver Sodium
nitrate Chloride Chloride nitrate
(ii) Na2SO4 + BaCl2 → BaSO4 + 2NaCl
Sodium Barium Barium Sodium
Sulphate Chloride Sulphate Chloride
(ppt)
(a) Oxidation: Reaction in which a substance gains oxygen or addition of oxygen or removal of hydrogen in a reaction is called oxidation.
Eg.:
(i) 2Cu + O2 → 2CuO
(ii) 4Al + 3O2 → 2Al2O3
(b) Reduction: Reaction in which a substance looses oxygen or removal of oxygen or gain of hydrogen in a reaction is called reduction.HEg.:
(i) CuO + H2 → Cu + H2O
oxygen is removed from copper oxide so reduction of CuO occurs.
(ii) H2S + Cl2 → 2HCl + S
gain of hydrogen by chlorine gas, so chlorine is reducted to form HCl.
The brown coloured element 'X' is copper. On heating in air it forms copper oxide which is black in colour.
2Cu(s) + O2(g) → 2CuO(s)
Copper Oxygen Copper oxide
(Brown (Black)
color)
Iron articles is painted to prevent from rusting, so that iron article is do not come in contact with atmosphere oxygen and moisture. This will prevented it from rusting.
As nitrogen is inert gas it doesnot react with oil and fat. Nitrogen gas prevent oil and fat containing food items from rancidity. Food items get rancid means it smells and tastes bad due to oxidation with the atmosphere oxygen.
Correct answer is (d).
In this example displacement reaction occurs, because Fe in Fe2O3 has been displaced by Al. Aluminium being more reactive than Iron, it displaces iron to form Aluminium oxide Al2O3.
(a) Corrosion: Metal are reacted with atmosphere oxygen, carbon dioxide and moisture and converted into metal oxides and carbonate. This phenomenon is called corrosion.
Eg.:
(i) Black coating on silver.
4Ag + 2H2S + O2 -----------> 2Ag2S + 2H2O
(ii) Green coating on copper.
Cu + CO2 + H2O -----------> CuCO3. Cu (OH)2
(b) Rancidity: Oil and fat containing items when comes in contact with atmosphere oxygen they get oxidised and start smelling and tasting bad. The food item have gone rancid. This phenomeon is called rancidity.
Eg.:
(i) Smell and taste on food items get change after some times.
Correct answe is (a).
Explanation : Fe + 2HCl → FeCl2 + H2
Iron Hydrochloric Ferrous Hydrogen
acid chloride gas
or Iron
chloride
A balanced chemical equation is an equation in which the number of each element are equal on the reactant side as well as in product side.
for example: BaCl2 + K2SO4 → BaSO4 + 2KCl
reactant side product side
Chemical equation should be balanced because only a balanced equation tells us the relative quantities of different reactants and product involved in the reaction.
(a) Hydrogen gas combines with nitrogen to form ammonia
H2 + N2 ---------→ NH3
Hydrogen gas nitrogen gas Ammonia
3H2 + N2 -----------→ 3NH3
Hydrogen gas NItrogen gas Ammonia
(b) Hydrogen sulphide gas burns in air to give water and sulpur dioxide
H2S(g) + O2(g) ----------------→ H2O(l) + SO2(g)
Hydrogen sulphide gas Oxygen (from air) water Sulpur dioxide
2H2S(g) + 3O2(g) --------------→ 2H2O(l) + 2SO2(g)
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate
BaCl2(aq) + Al2(SO4)3(aq) --------→ AlCl3(aq) + BaSO4(s)
Barium chloride Aluminium sulphate Aluminium chloride Barium sulphate
3BaCl2(aq) + Al2(SO4)3(aq) -------→ 2AlCl3(aq) + 3BaSO4(s)
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas
K(s) + H2O(l) -----→ KOH(aq) + H2(g)
Potassium Water potassium hydroxide hydrogen gas
2K(s) + 2H2O(l) ------- → 2KOH(q) + H2(g)
(a) 2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O
(b) 2NaOH + H2SO4 → Na2SO4 + 2H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + 2HCl
(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
Ca(OH)2 + CO2 → CaCO3 + H2O
(b) Zinc + Silver nitrate → Zinc nitrate + Silver
Zn + AgNO3 → Zn(NO3)2 + Ag
(c) Aluminium + Copper chloride → Aluminium chloride + Copper
2Al + 3CuCl2 → 2AlCl3 + 3Cu
(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride
BaCl2 + K2SO4 → BaSO4 + 2KCl
(a) 2KBr + BaI2 → 2KI + BaBr2
Type of reaction: Double displacement reaction. Because the cation K+ and Ba2+ have exchanged their anions Br- and SO42- .
(b) ZnCO3 → ZnO + CO2
Type of reaction: Decomposition reaction. Because in this reaction single reactant break down into two product
(c) H2 + Cl2 → 2HCl
Type of reaction: Combination. Because in this reaction two reactant combine into single product.
(d) Mg + 2HCl → MgCl2 + H2
Type of reaction : disclacement reaction because H in HCl has been displaced by Mg.
Exothermic reaction: A reaction in which energy is released in the form of heat or light.
Eg.: Burning of Natural gas (methane)
CH4(g) + O2(g) → CO2(g) + H2O(l) + Heat
Endothermic reaction: A reaction in which energy is absorbed from the surroundings and cooling is produced.
Eg.: Decomposition of calcium carbonate
CaCO3(s) -------------→ CaO(s) + CO2(g)
Calcium Carbonate Calcium oxide Carbon dioxide
or Lime stone or quick lime
