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(b) Na₂Cr₂O₇ is preferred over K₂Cr₂O₇ in volumetric analysis

1. a) Physical change

2. b) GroWth of a tree

3. c) Occurrence of tides in sea

4. b) Chemical change

Correct answer is (a) Earthquake

Correct option is B) physical change

Correct option is B) White

Correct option is C) chemical change

Correct option is A) Calcium carbonate

P-Ethanol, Q-Ethanoic acid., R-Hydrogen

CH₃CH₂OH+Acidified → K₂Cr₂O₇  CH₃COOH

2CH₃COOH+2Na → 2CH₃COONa+H₂

Magnesium ribbon must be cleaned before burning. So that the layer of magnesium oxide can be removed in order to get the desired chemical reaction. 

Magnesium ribbon burns in air with a dazzling flame and forms a white ash, I magnesium gets oxidised to magnesium oxide.

Correct option is A) Magnesium Oxide

When iron nail is dipped in the solution of copper sulphate, copper is displaced by iron and forms ferrous sulphate. Thus the blue colour of copper sulphate changes into green because of formation of ferrous sulphate.

Correct option is C) brown colour

Physical changes

1. Bending a paper clip. 

2. Pounding silver into thin plate. 

3. Rolling a chapathi dough into thin wire. 

4. Occurrence of a day and night. 

5. Blinking of eyelids. 

6. Occurrence of a thunderstorm. 

7. Rotation of the earth.

8. Formation of eclipses. 

9. Painting the grill.

10. A rough piece of wood is sanded and polished resulting in change in texture. 

11. Dosa from the batter.

Chemical changes 

1. Rusting of a iron 

2. Eruption of volcano 

3. Burning of matchstick.

1. Take a small piece of Magnesium ribbon. Burn it on a flame of candle. 

2. We will find brilliant white dazzling light leaving a powdery substance behind. 

3. When Magnesium burns in the presence of Oxygen, it forms Magnesium Oxide in the form of powder ash, which is a new substance. 

4. Thus there is a change in the composition.

5. Magnesium + Oxygen → Magnesium Oxide. 

6. Collect the ash and mix it with a small quantity of water and dissolve it. Another new substance is formed. 

7. Magnesium Oxide + Water → Magnesium Hydroxide 

8. Test the dissolved mixture with blue and red litmus papers to decide whether it is a acid or a base. 

9. We notice that the litmus paper turns blue. 

10. This means that magnesium hydroxide is basic in nature. 

11. As all these are new substances all these changes are chemical changes.

Except radon which is radioactive, Xenon has least ionisation energy among noble gases and hence it readily forms chemical compounds particularly with O₂ and F_2.

(ii, iii) The linear shape of CO₂ is due to pπ-pπ bonding between carbon and oxygen and sp hybridisation of carbon.

P₄ + 10 SO₂Cl₂ → 4PCl₅ + 10SO₂

The compound of phosphorus is.

H₃PO₄

The formula of the compound of iodine is

HIO₃

2F₂ +2H₂O → 4HF+ O₂ HF and O₂ are produced.

On moving from left to right in a period, the tendency of atoms to gain electrons increases.

(a) Iron (III) Chloride: Iron chloride is formed by direct combination of elements. 

2Fe + 3Cl₂ ⟶ 2FeCI₃ 

(b) Sodium sulphate: By neutralization of caustic soda with dilute sulphuric acid 

2NaOH + H₂SO₄ ⟶ Na₂SO₄ + 2H₂O 

(c) Sodium zincate: By the action of metals with alkalis 

Zn + 2NaOH ⟶ Na₂ZnO₂ + H₂ 

(d) Iron (II) sulphate: Iron sulphate is prepared by the action of dilute acid on an active metal. 

Fe + H₂SO₄ ⟶ FeSO₄ + H₂ 

(e) Sodium chloride: By the neutralization reaction of strong acid with strong base

 NaOH + HCI ⟶ NaCI + H₂O

We can distinguish between iron (II) chloride and iron (III) chloride by using NaOH. 

When NaOH reacts with iron (II) chloride, it forms a dirty green precipitate whereas 

when NaOH reacts with iron (III) chloride, it forms a brown gelatinous precipitate.

Strong bases like potassium hydroxide (KOH), sodium hydroxide (NaOH) are corrosive in nature. So they can harm the internal organs. Therefore we should not use them as antacid.

Answer is Yes

The answer is (b) All metal oxides react with water to give salt and acid

Metal oxides are basic in nature hence they give alkaline solution when dissolved in water.

The answer is (d) C₂H₅OH

C₂H₅OH is an alcohol not a base

 The answer is (b) Citric acid

Citric acid is the organic acid hence it is the answer

The correct option is (a) (i) and (ii)

• Reaction of water with quick lime is exothermic reaction. 
• When water is added to quicklime, then calcium hydroxide is formed with large amount of heat is released in the process.
• Dilution of an acid is exothermic reaction.

C + 4HNO₃ → 2H₂O + 4NO₂ + CO₂

The correct answer is

(B) brown

Classical qualitative analysis method includes separation and identification of compounds.

• Separations may be done by methods such as precipitation, extraction and distillation.
• Identification may be based on differences in colour, odour, melting point, boiling point, and reactivity.

KCl (aq) + AgNO₃ (aq) → AgCl (s) + KNO₃ (aq) 

It is a double displacement and precipitation reaction

(i) X→ Quick lime, fcrrmula - CaO

(ii) CaO + H₂O→ Ca(OH)₂

(i) Before heating: Pale green

After heating: Brown or reddish brown.

(ii) SO₂ and SO₃.

(iii) 2FeSO₄(s) + Heat → Fe₂O₃(s) + SO₂(g) SO₃(g)

When food containing fat or oil is not used and left over for a long time, their smell and taste changes because of fats and oils getting slowly oxidized. This process is called rancidity.

Two methods which are used to slow down the oxidation process are:

(i) keeping food in the airtight container.

(ii) flushing the bags containing food with nitrogen gas.

(i) 2Na + 2H₂O → 2NaOH + H₂

It is an exothermic reaction.

(ii)2FeSO₄(s) → Fe₂O₃ + SO₂(g) + SO₃(g)

It is an endothermic reaction.

(A) \(CO_2\)

Let say, the molar mass of unknown gas is M

Then, Number of mole of unknown gas = \(\frac{4.4\,g}{M}\)

As we know,

1 mole of any gas at STP occupy = 22.4 L of volume.

\(\therefore\) Number of moles unknown gas = \(\frac{2.24}{22.4}=0.1\) mol

Therefore,

\(\frac{4.4}{M}=0.1\)

\(M=\frac{4.4}{0.1}\)

M = 44 g/mol

In the given options only \(CO_2\) has molar mass of 44 g/mol

Hence, the unknown gas will be \(CO_2\).

Option : (A) CO₂

• Analytical chemistry has applications in forensic science, engineering and industry.
• Analytical chemistry is also useful in the field of agriculture and pharmaceutical industry.
• Industrial process as a whole and the production of new kinds of materials are closely associated with analytical chemistry.

1. Qualitative analysis deals with the detection of the presence or absence of elements in compounds and of chemical compounds in mixtures.

2. Quantitative analysis deals with the determination of the relative proportions of elements in compounds and of chemical compounds in mixtures.

i. (2.5 × 10^-6) × (1.8 × 10^-7) 

= (2.5 × 1.8) (10^-6+(-7))

= (2.5 × 1.8) × (10^-6-7)

= 4.5 × 10^-13

ii. (4.5 × 10^-3) × (1.8 × 10³)

= (4.5 × 1.8) (10^-3+3)

= (4.5 × 1.8) × (10⁰)

= 8.1

iii. (8.5 × 10⁷) × (3.5 × 10⁹)

= (8.5 × 3.5) (10⁷⁺⁹)

= (8.5 × 3.5) × 10¹⁶

= 29.75 × 10¹⁶

= 2.975 × 10¹⁷

[Note : To express number in scientific notation, the number has to be greater than or equal to 10 or less than 1. The number, 8.1 is greater than 1, but less than 10 and hence, it cannot be expressed in scientific notation.]

The observed value is 20.20 g and accepted (true) value is 20.15 g.

i. Absolute error = Observed value – True value

= 20.20 – 20.15

= 0.05 g

ii. Relative error = \(\frac{Absolute\,error}{True\,value}\) x 100%

= \(\frac{0.05}{20.15}\) x  100%

= 0.25%

∴ i. Absolute error = 0.05 g 

ii. Relative error = 0.25 %

B) In black and white photography

Correct option is A) 1, 2

The radius of cation is smaller than that of the parent atom. Cation is formed by the loss of one or more electron from the gaseous atom. Now, in the cation the nuclear charge remains the same that in the parent atom but the number of electrons becomes less. As a result of this, the nuclear hold on the remaining electrons increases because of the increase in the effective nuclear charge per electron. This causes a decrease in the size.

The radius of anion is larger than that of parent atom. Anion is formed by the gain of one or more electrons by the gaseous atom. In the anion the nuclear charge is the same as that in the parent atom but the number of electrons has increased. Since same nuclear charge now acts on increased number of electrons, the effective nuclear charge per electron decreases in the anion. The electron cloud is held less tightly by the nucleus. This causes increase in the size.

Silver chloride (Agcl) and Silver bromide (AgBr)

2AgCl+ Sunlight →  2Ag+Cl₂

2AgBr +Sunlight → 2Ag+Br₂ 

Those reactions in which energy is absorbed (in form of heat, light or electricity) to break down the reactants is called decomposition reaction. 

(i) In white washing, quicklime reacts with water to form slaked lime.

CaO+H₂O → Ca(OH)₂+Heat

CaO+H₂O-Quick lime 

Ca(OH)₂  -Slaked lime

(ii) Silver bromide,  when exposed to light decomposes to silver and bromine.

2AgBr(s) +sunlight → 2Ag(s)+Br₂(g)

2AgBr(s)-Silver bromide

2Ag(s)-Silver

Br₂(g)- Bromide

Mass of HNO₃ = 1.8 g,

Volume of solution = 250 mL = 0.250 L

To find : 

Molarity

Formulae :

i. Number of moles = \(\frac{Mass\,of\,substance\,in\,grams}{Molar\,mass\,of\,substance}\)

ii. Molarity (M) = \(\frac{Number\,of\,moles\,of\,solute}{Volume\,of\,solution\,in\,litres}\)

Calculation : 

Molar mass of HNO₃ = 63 g mol^-1

Using formula (i),

Number of moles = \(\frac{Mass\,of\,substance\,in\,grams}{Molar\,mass\,of\,substance}\) 

= \(\frac{1.8}{63}\)

= 0.0286 mol 

Using formula (ii),

Molarity (mol/L) = \(\frac{Number\,of\,moles\,of\,solute}{Volume\,of\,solution\,in\,litres}\)

= \(\frac{0.0286\,mol}{0.250L}\) 

= 0.114 M

∴ Molarity of the HNO₃ solution = 0.114 M

(i) 1 mole = 6.022 × 10²³

0.1 mole = 0.1 × 6.022 × 10²³ = 6.022 × 10²² molecules

1 mole of sulphur (S₈) contains = 8 atoms

Hence, no of atoms present = 8 × no. of molecules

⇒ Number of atoms present = 8 × 6.022 × 10²² molecules

⇒ Number of atoms present = 4.8 × 10²³ atoms

Thus, number of atoms present in 0.1 mole of sulphur is 4.8 × 10²³ atoms.

(ii) 1 mole = 6.022 × 10²³

2 mole = 2 × 6.022 × 10²³ molecules

1 mole of phosphorus (P₄) contains = 4 atoms

Hence, no of atoms present = 4 × no. of molecules

⇒ Number of atoms present = 4 × 2× 6.022 × 10²³ molecules

⇒ Number of atoms present = 4.8 × 10²⁴ atoms

Thus, number of atoms present in 2 mole of phosphorus is 4.8 × 10²⁴ atoms.