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(b) Copper (Cu) 

(c) Copper sulphate (CuSO₄) 

(d) Displacement reaction; CuSO₄ (aq) + Zn (s) ZnSO₄ (aq) + Cu (s) 

(e) Brass

(a) Zinc and Iron. 

(b) Dilute hydrochloric acid and dilute sulphuric acid. 

(c) Hydrogen. 

(d) Lighter than air. 

(e) Exothermic. 

(f) Suppose metal X is zinc (Zn) and acid Y is dilute hydrochloric acid (HCl) ;

Zn (s) + 2HCl (aq) ZnCl₂ (aq) + H₂ (g)

(a) Magnesium Ribbon is heated in the presence of air to form a white powder called magnesium oxide. 

(b) When dilute sulphuric acid is poured over zinc granules 

1. there will be a rise in temperature 

2. evolution of hydrogen gas.

(c) 

1. A yellow precipitate is formed. 

2. There will be a change in color (from colourless to yellow).

Displacement reaction: More active element replaces less active element from its compound in a chemical reaction.

(a) The various characteristics of chemical reactions are: 

1. Evolution of a gas 

2. Formation of a precipitate 

3. Change in colour 

4. Change in temperature 

5. Change in state. 

(b) 1. Evolution of carbon dioxide gas 

2. Change in colour from purple to colourless 

3. Formation of white precipitate of barium sulphate 

4. Change in temperature 

5. Change in state from solid to liquid and gas.

In a displacement reaction, one element replaces another element from a compound.

The change in which a substance or substances are converted into a new substance or substances, possessing properties altogether different from the original ones, is called a chemcial change. During this change, the original substance cannot be recovered by any simple means. This change is permanent.

A reaction in which two or more simpler substances combine to form a single product.

C+O₂ + Burn→CO₂

2H₂+O₂ → 2H₂O

A process in which two or more substances react to form some other new substances with new set of properties is called a chemical reaction

The simple representation or a chemical reaction in a condensed form with the help of chemical formulae is called a chemical equation.

(a) Chemical reactions are the processes in which new substances with new properties are formed. 

For example: When magnesium ribbon is heated, it burns in air to form a white powder called magnesium oxide. 

(b) 1. The chemical reaction between zinc and dilute sulphuric acid.

 2. The chemical reaction between citric acid and purple coloured potassium permanganate solution is characterised by change in colour (from purple to colourless). 

3. The chemical reaction between potassium iodide and lead nitrate is characterised by the formation of a yellow precipitate of lead iodide.

 4. The reaction between quick lime and water to form slaked lime is characterised by a change in temperature. 

5. When wax is burned, then water and carbon dioxide are formed. Wax is a solid;

water is a liquid whereas carbon dioxide is a gas.

The reaction in which the place of the ion of a less reactive element in a compound is taken by another more reactive element by formation of its own ions, is called displacement reaction.

A single substance is broken down and two or more substances are formed during a decomposition reaction.

(1) while writing a chemical equation, gaseous, 1iquid and solid states are symbolised as (g), (l) and (s) respectively.

(2) This is done to make it more informative and to emphasise that those reactions occur in that manner only under those conditions. Hence, physical states of reactants and products are mentioned while writing a chemical equation.

The simple form or representation or a chemical reaction in words is known as word equation.

A single compound (product) is formed from two or more substances during a combination reaction.

Acetic acid is formed in the oxidation of ethyl alcohol.

Molecular mass of HNO₃ (M) 

= (Atomic mass of H) x 1 + (Atomic mass of N) x 1 + (Atomic mass of O) x 3

= (1 x 1)+ (14 x 1)+ (16 × 3) 

= 1 + 14 + 48 

= 63 

Molecular mass of HNO₃ (M) = 63

Molecular mass of MgO(M) 

= (Atomic mass of Mg) x 1 + (Atomic mass of O) x1

= (24 x 1) + (16 x 1) 

= 24 + 16

= 40 Molecular mass of MgO (M) = 40

From the description, it can be concluded that the element of the coin is copper.

On being heated copper gets oxidized due to the presence of oxygen in air which results in the formation of copper oxide (precisely cupric oxide) which is black in color. 

The reaction is as follows: 

2Cu + O₂→ 2CuO

Molecular mass of H₂SO₄ (M) 

= (Atomic mass of H) x 2 + (Atomic mass of S) x 1 + (Atomic mass of O) x 4 

= (1 x 2) + (32 x1) + (16×4) 

= 2 + 32 + 64 

= 98 

Molecular mass of H₂SO₄ (M) = 98

(a) Those reactions in which one element takes the place of another element in a compound, are known as displacement reactions. 

Example: CuSO₄ (aq) + Zn (s) —–>ZnSO₄ + Cu 

When a strip of zinc metal is placed in copper sulphate solution, then zinc sulphate solution and copper are obtained. In this reaction, zinc displaces copper from copper sulphate compound so that copper is set free. The blue colour of copper sulphate solution fades due to the formation of zinc sulphate. 

(b) Those reactions in which two compounds react by an exchange of ions to form two new compounds are called double displacement reactions.

Example: AgNO₃ (aq) + NaCl (aq)

When silver nitrate solution is added to sodium chloride solution, then a white precipitate of silver chloride is formed along with sodium nitrate solution. In this reaction, two compounds, silver nitrate and sodium chloride, react to form two new compounds, silver chloride and sodium nitrate.

(a) (i) H₂S + Cl₂ —–>S + 2HCl In this reaction, H₂S is changing into S. That is, Hydrogen is being removed from hydrogen sulphide. Now, by definition, the removal of hydrogen from a compound is called oxidation, so, we can say that hydrogen sulphide is being oxidised to sulphur. On the other hand, Cl₂ is changing into HCl. That is, hydrogen is being added to chlorine. By definition, the addition of hydrogen to a substance is called reduction, so we can say that chlorine is being reduced to hydrogen chloride. 

(b) 2Mg + O₂ —–>2MgO 

(i) Mg (ii) O₂ 

Physical changes: Evaporation of petrol, heating of an iron rod to red hot, sublimation of solid ammonium chloride.
Chemical changes: Burning of Liquefied Petroleum Gas (LPG), curdling of milk.

(a) Silver metal does not react with dilute HCl 

(b) The temperature of the reaction mixture rises when aluminium is added because it is an exothermic reaction. 

(c) Reaction of sodium metal is found to be highly explosive because it is an exothermic reaction 

(d) When lead is treated with hydrochloric acid, bubbles of hydrogen gas are evolved 

Pb + 2HCl → PbCl₂ + H₂

The electrons present in the outermost orbit of an atom are called valence electrons.

Double Displacement Reaction is a type of chemical reaction in which anions and cations of the reacting compounds exchange their positions to form different compounds. 

The precipitation reaction is a type of reaction in which one of the reactants is solvent and one of the products formed is insoluble in the solvent. 

So the example of double displacement and precipitation reaction is as follows: 

AgNO₃ + NaCl → AgCl (White Ppt.) + NaNO₃

Whenever a metal is exposed to air and water for a long time it gets surrounded by a layer due to any type of chemical reactions and gets corroded. This process is called corrosion. So when a silver article gets a black coating, the phenomenon is called as corrosion.

When an electric current is passed through fused lead bromide, lead bromide being an ionic compound gets dissociated into lead and bromide ions.

The reaction is as follows: 

PbBr₂ (Lead Bromide) → Pb₂ (Lead Ions) + 2Br ^- (Bromide Ion)

Correct answer: (d) NA

The reaction which is completed in short time i.e. occurs rapidly is called fast speed reaction.

The rusting of iron is an oxidation process. The rust on iron does not form by a simple reaction between oxygen and iron surface. The rust is formed by an electrochemical reaction. Fe oxidises to Fe₂O₃. H₂O on one part of iron surface while oxygen gets reduced to H₂O on another part or surface, Different regions on the surface of iron become anode and cathode.

(1) Fe is oxidised to Fe²⁺ in the anode region.

Fe_(s) → Fe²⁺ (_aq) + 2^e-

(2) O₂ is reduced to form water in the cathode region.

O_2(g) + 4H⁺ _(aq) + 4e —→ 2H₂O_(I)

When Fe²⁺ ions migrate from the anode region they react with water and futher get oxidised to form Fe³⁺ ions.

A reddish coloured hydrated oxide is formed from Fe3+ ions. It is called rust. It collects on the surface

2Fe³⁺ _(aq) + 4H₂O_(I) → Fe₂O₃. H₂O_(s) + 6H⁺ _(aq)....

Because of various components in the atmosphere, oxidation of metals takes place, consequently resulting in their damage. This is called ‘corrosion’. Iron rusts and a reddish coloured layer is formed on it. This is corrosion of iron.

(i) Photochemical decomposition:

single reactant breaks down to give simpler products.

While silver chloride changes to grey, as it decomposes to silver and chlorine in the presence of sunlight.

(ii) 2AgCl(s) +Sunlight → 2Ag(s) + Cl₂(g)

(iii) Black and white photography.

The chemical reaction in which a single product is formed two or more reactants and energy is evolved is known as combination reaction.

Example: 2Mg + O₂+Burn → 2MgO

When a single reactant on gaining energy decomposes to give two or more simple products, such a reaction is called a decomposition reaction.

Example:

CaCO₃+Heat → CaO+CO₂

A reaction  is considered a double displacement reaction if during the chemical reaction an exchange of ions takes place between two ionic substances.

 Example: BaCl₂+Na₂SO₄ → BaSO₄+2NaCl

ln a displacement reaction, a more reactive element displaces or removes another less reactive element. from its compound

e.g. Fe+CuSO₄ → FeSO₄+Cu

whereas in a double displacement reaction, the compounds react by exchanging their ions and from two new compounds.

Correct answer: (c) \(HO_{3}^{-}\) 

Correct answer: (c) NH

Iron will react only with CuSO₄ solution as Fe is more reactive than Cu.

ZnO(s) and CO2(g) are formed.

Chemical Equation :

ZnCO₃ →ZnO+CO₂

When a solution of sodium sulphate is rnixed with a solution of barium chloriiie, ihe foilorving double displacement reaction takes place :

Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCI(aq)

in this reaction, sulphate ions from sodium sulphate are displaced by chloride ions  (Cl^- ) and chloride ions in barium chloride are displaced by sulphate ions. As a result, a white precipitate of barium sulphate is formed and sodium chloride remains in the solution.

Carbon Dioxide when dissolved in water leads to the formation of a weak acid which is called carbonic acid. 

Reaction is as follows: 

CO₂ + H₂O → H₂CO₃

Breaking of bonds is called as Bond Dissociation [Dissociate means to break]. Bond Dissociation is an endothermic reaction which means that energy is absorbed in breaking of a bond. 

Making of a bond is called as Bond Formation. This reaction is exothermic in nature which means that energy is given off or liberated while the formation of bonds.

In the case of Aluminium, Corrosion is not harmful. Because the new layer of corroded aluminium it-self act as a prevention for further corrosion.

Corrosion of iron is a serious problem because it leads to wastage of tonnes of iron every year and lot of money is spent to repair or replace it.

Following four factors are responsible for corrosion of Iron: 

i) Moisture: Moisture reacts with iron to form rust(Mixture of Iron oxide and water) 

ii) Oxygen: Oxygen reacts with iron to form Iron oxide which on combining with moisture becomes rust

iii) Poor maintenance: Poor maintenance leads to continuous exposure of iron to moisture and air which causes rust.

 iv) Poorly built iron substances: If other substances like carbon, are not mixed while making iron substances in proper proportions, It gets rusted.

• The electronic configuration of Mn is ₂₅Mn [Ar] 3d⁵ 4s² 
• In + 2 and + 3 oxidation states, the electronic configuration of Mn²⁺ is, Mn²⁺ [Ar] 3d⁵ and Mn³⁺ [Ar] 3d⁴ 
• Since half-filled d-orbital (3d5) has more stability and lower energy than 3d⁴, Mn²⁺ is more stable than Mn³⁺
• The electronic configuration of Fe is ₂₆Fe [Ar] 3d⁶ 4s In + 2 and + 3 oxidation states of Fe, the electronic configuration is, Fe²⁺ [Ar] 3d⁶ and Fe³⁺ [Ar] 3d⁵ Since half-filled orbital is more stable, + 3 state of Fe is more stable than + 2 state.

Correct option is: (d) All the three (a), (b) and (c) are correct

(a) (i) Ca(OH)₂+CO₂ → CaCO₃+H₂O

(ii) Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)

CaCO₃(s) + H₂O(l)+CO₂(g) → Ca(HCO₃)₂(aq)

(b) Aragonite and calcite

Correct option is: Correct set up D.