Chemistry

1.13. Pressure is determined as force per unit area of the surface. The S.I. unit of pressure, pascal, is as shown below:

1 Pa = 1 Nm^-2_.

If mass of air at sea level is 1034 g cm^-2, calculate the pressure in pascal.

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1.13. Pressure= Force/Area

But weight = m x g, where m = mass (in kg) and g = 9.8 m/s²

Therefore, Pressure = 1034 g cm^-2x 9.8 m/s²

= 1034 x 10^-3 kg x (100 m)²x 9.8 m/s²

= 101332 Pa

= 1.01332 x 10⁵ Pa

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11 months ago

1.12. If the density of methanol is 0.793 kg L ^-1, what is its volume needed for making 2.5 L of its 0.25 M solution?

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1.12. Density of methanol = 0.793 kg/L, molar mass of methanol (CH₃OH) = 32g/mol = 0.032 kg/mol

V₁ =? , V₂ = 2.5 L, M₂ = 0.25 M

We can apply the formula of

M₁V₁ = M₂V₂

Or V₁ = M₂V₂/M₁

Substituting M₁ = density / molar mass, we get

M₁ = 0.793/0.032 = 24.78

V₁ = 0.25 x 2.5 / 24.78 = 0.02522 L = 25.22 mL

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11 months ago

1.11. What is the concentration of sugar (C₁₂H₂₂O₁₁) in mol L ^-1if its 20 g are dissolved in enough water to make a final volume up to 2 L?

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1.11. Molar mass of sugar = (12 x 12) + (22 x 1) + (11 x 16) =342 g/mol

No. of moles in 352 g of sugar = 1 mol

No. of moles in 20 g = 20 x 1/352 = 0.0585 mol

Therefore, molar concentration = moles of solute / volume of solution in L = 0.0585 / 2 = 0.0293 mol/L

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11 months ago

11.24. How would you explain the lower atomic radius of Ga as compared to Al?

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Due to poor shielding effect of d-electrons in Ga, the electrons in gallium experience great force of attraction by nucleus as compared to Al. That is why Ga has lower atomic radius as compared to Al.

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11.23. Explain why is there a phenomenal decrease in ionization enthalpy from carbon to silicon?

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Because there is increase in atomic size on moving from carbon to silicon, the screening effect increases. Thus, the force of attraction of nucleus for the valence electron in silicon decreases as compared to carbon. Therefore, the ionization enthalpy decreases from carbon to silicon.

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11.22. Give reasons:

(i) Conc. HNO₃ can be transported in aluminium container.
(ii) A mixture of dilute NaOH and aluminium pieces is used to open drain.
(iii) Graphite is used as lubricant.
(iv) Diamond is used as an abrasive.
(v) Aluminium alloys are used to make aircraft body.
(vi) Aluminium utensils should not be kept in water overnight.
(vii) Aluminium wire is used to make transmission cables.

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(i) Al reacts with conc. HNO₃ to form a very thin film of aluminium oxide on its surface which protects it from further reaction. That is why conc. HNO₃ can be transported in aluminium container.
2Al (s) + 6HNO₃ (conc.) → Al₂O₃ (s) + 6NO₂ (g) + 3H₂O (l)

(ii) NaOH reacts with Al to evolve H₂ gas. Thus, the pressure of the gas produced can be used for opening or cleaning clogged drains.
2Al (s) + 2NaOH (aq) + 2H₂O (l) → 2NaAlO₂ (aq) + 3H₂ (g)

(iii) Graphite has layered structure which are held by weak van there Waals forces. Thus, graphite cleaves easily between the layers, therefore it is very soft and slippery. That is why

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11 months ago

1.10. In three moles of ethane (C₂H₆), calculate the following:

(i) Number of moles of carbon atoms

(ii) Number of moles of hydrogen atoms

(iii) Number of molecules of ethane

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1.10. (i) 1 mole of C₂H₆ contains 2 moles of carbon atoms

Therefore, no of moles of C atoms in 3 moles of C₂H₆ = 6 moles
(ii) 1 mole of C₂H₆ contains 6 moles of hydrogen atoms
Therefore, no of moles of H atoms in 3 moles of C₂H₆ = 18 moles

(iii) 1 mole of C₂H₆ contains 6.02 x 10²³ molecules

Therefore, 3 moles of C₂H₆will contain ethane molecules = 3 x 6.02 x 10²³ molecules= 18.06 x 10²³ molecules

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11.21. Explain the following reactions
(a) Silicon is heated with methyl chloride at high temperature in the presence of copper;
(b) Silicon dioxide is treated with hydrogen fluoride;
(c) CO is heated with ZnO;
(d) Hydrated alumina is treated with aqueous NaOH solution.

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(a) Silicon is heated with methyl chloride at high temperature in the presence of copper catalyst at 537 K, methyl substituted chlorosilanes MeSiCl₃, Me₂→SiCl₂→, Me₃→SiCl and Me₄→Si are formed.

(b) When silicon dioxide is treated with hydrogen fluoride, first SiF₄→ is formed and then hydro fluorosilicic acid is obtained.
SiO₂ →+ 4HF → SiF₄ →+ 2H₂→O
SiF₄+2HF → H₂SiF₆

(c) When CO is heated with ZnO, ZnO is reduced to Zn metal.
CO + ZnO →CO₂ →+ Zn

(d) When hydrated alumina is treated with aqueous NaOH solution, it dissolves to form sodium meta aluminate.
Al₂→O₃→.2H₂→O+2NaOH→

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1.9. Calculate the atomic mass (average) of chlorine using the following data:

	% Natural Abundance	Molar Mass
³⁵Cl	75.77	34.9689
³⁷Cl	24.23	36.9659

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1.9. Average atomic mass = (Fractional abundance of ³⁵Cl x molar mass of ³⁵Cl) + (Fractional abundance of ³⁷Cl x molar mass of ³⁷Cl)

= (75.77/100 x 34.9689) + (24.23/100 x 36.9659)

= 26.4959 + 8.9568

= 35.4527

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11.20. What happens when
(a) Borax is heated strongly,
(b) Boric acid is added to water,
(c) Aluminium is treated with dilute NaOH,
(d) BF₃ is reacted with ammonia?

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