Vardaan Learning Institute

Ans: (b) $4Na + O_2 \rightarrow 2Na_2O$
Both reactants (Sodium and Oxygen) are elements combining to form a compound.

Ans: (d) a yellow residue is left
$2Pb(NO_3)_2 \xrightarrow{\Delta} 2PbO + 4NO_2 + O_2$.
$PbO$ (Lead Oxide) is yellow in colour.

Ans: (b) Sublimation of dry ice
Sublimation requires absorption of heat (energy). Others are exothermic.

Ans: (b) $CO$
$CO$ gains oxygen to become $CO_2$, so it is oxidized and acts as the reducing agent.

Ans: (a) Hydrogen gas and iron chloride
$Fe + 2HCl \rightarrow FeCl_2 + H_2$.

Ans: (b) Exothermic reaction
Decomposition of vegetable matter into compost releases heat energy, so it is an exothermic reaction.

Ans: (d) All of these
Antioxidants, air-tight containers, and nitrogen flushing all help prevent oxidation of fats/oils.

Ans: (b) 2:1
Water ($H_2O$) decomposes into hydrogen and oxygen. The balanced equation ($2H_2O \rightarrow 2H_2 + O_2$) shows 2 moles of $H_2$ for 1 mole of $O_2$.

Ans: (d) Helium or nitrogen
Inert gases like Nitrogen or Helium prevent contact with oxygen, preventing rancidity.

Ans: (c) Atoms of one element change into those of another element to form new products
In a chemical reaction, atoms are conserved; they are merely rearranged. Transmutation of elements occurs in nuclear reactions, not chemical ones.

Ans: (a) Both A and R are true and R is the correct explanation of A.
Silver chloride decomposes in sunlight to form Silver (grey) and Chlorine. $2AgCl \rightarrow 2Ag + Cl_2$.

Ans: (d) A is false but R is true.
Burning of Magnesium is a chemical change because a new substance (MgO) is formed.

Ans: (a) Both A and R are true and R is the correct explanation of A.
$2Cu + O_2 \rightarrow 2CuO$. Copper gains oxygen, so it undergoes oxidation. A substance that undergoes oxidation acts as a reducing agent.

Ans: (a) Both A and R are true and R is the correct explanation of A.
Equations are balanced to equate the number of atoms on both sides, satisfying the Law of Conservation of Mass.

(i) $2HNO_3 + Ca(OH)_2 \rightarrow Ca(NO_3)_2 + 2H_2O$
(ii) $2NaOH + H_2SO_4 \rightarrow Na_2SO_4 + 2H_2O$
(iii) $NaCl + AgNO_3 \rightarrow AgCl + NaNO_3$ (Already balanced)

(i) 'X' is Calcium Oxide (Quick lime). Formula: $CaO$.
(ii) $CaO(s) + H_2O(l) \rightarrow Ca(OH)_2(aq) + \text{Heat}$
(iii) Calcium hydroxide reacts slowly with $CO_2$ in air to form a thin layer of Calcium Carbonate ($CaCO_3$) which gives a shiny finish.
$Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O$.

The blue colour fades because Iron displaces Copper from Copper Sulphate solution as Iron is more reactive than Copper.
$Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s)$
Type: Displacement Reaction.

A reaction in which an insoluble substance (precipitate) is formed is called a precipitation reaction.
Example: $Na_2SO_4(aq) + BaCl_2(aq) \rightarrow BaSO_4(s) + 2NaCl(aq)$ (White ppt of $BaSO_4$).
Difference: In neutralisation (Double Displacement), e.g., $HCl + NaOH \rightarrow NaCl + H_2O$, no precipitate is formed.

(a) $Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O$
(b) $Zn + 2AgNO_3 \rightarrow Zn(NO_3)_2 + 2Ag$
(c) $2Al + 3CuCl_2 \rightarrow 2AlCl_3 + 3Cu$

A reaction in which oxidation and reduction occur simultaneously is called a redox reaction.
Example: $CuO + H_2 \xrightarrow{\Delta} Cu + H_2O$.
For given reaction: $MnO_2 + 4HCl \rightarrow MnCl_2 + 2H_2O + Cl_2$
Substance Oxidized: $HCl$ (loses Hydrogen/gains electronegative element to form $Cl_2$).
Substance Reduced: $MnO_2$ (loses Oxygen to form $MnCl_2$).

(i) Corrosion: Slow eating up of metals by action of air and moisture. Conditions: Presence of Air ($O_2$) and Moisture ($H_2O$).
(ii) (a) Painting (b) Greasing/Oiling.
(iii) Rust: $Fe_2O_3 \cdot xH_2O$ (Hydrated Iron(III) Oxide).
(iv) Rancidity: The oxidation of fats and oils in food resulting in bad smell and taste. Prevention: Adding antioxidants (BHA, BHT) or flushing with Nitrogen gas.

(a) Double Displacement Reaction (Precipitation).
(b) Oxidation Reaction (or Combination).
(c) Decomposition Reaction (Thermal).
(d) Displacement Reaction.
(e) Combination Reaction (Exothermic).

(i) Combination Reaction.
(ii) Energy is released (Exothermic).
(iii) $CaO(s) + H_2O(l) \rightarrow Ca(OH)_2(aq) + \text{Heat energy}$.

(i) Hydrated Iron(III) oxide, $Fe_2O_3 \cdot xH_2O$.
(ii) Presence of Air (Oxygen) and Moisture (Water).
(iii) Methods: 1. Painting or Oiling 2. Galvanization (coating with Zinc).