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IB Chemistry HL2.2 The covalent modelQuestion Bank

2.2 The covalent model

Question 1

[Maximum number: 5]

Methanoic acid (HCOOH) is the first member of the homologous series of carboxylic acids.

Question 1(c)

(a)

Methanoic acid and ethanal (CH3CHO)\left(\mathrm{CH}_{3} \mathrm{CHO}\right) both contain a carbonyl group and have similar molar masses.

[ 3 ]

Question 1(c)(i)

(i)

Explain why, in terms of the strongest intermolecular forces between the molecules, ethanal has a much lower boiling point than methanoic acid.

[ 2 ]

Question 1(c)(ii)

(ii)

Outline why ethanal and methanoic acid are both fully miscible with water.

[ 1 ]

Question 1(d)

(b)

Methanoic acid acts as a weak monobasic acid in aqueous solution.

[ 2 ]

Question 1(d)(iv)

(i)

Explain why the two carbon-oxygen bonds in the methanoate ion are of equal length, and compare their length to the carbon-oxygen bonds in methanoic acid.

[ 2 ]

Question 1

[Maximum number: 1]

One definition of atomic volume is given by the formula:

 Atomic volume = atomic mass (g mol−1) density (g cm−3)\text { Atomic volume }=\frac{\text { atomic mass }\left(\mathrm{g} \mathrm{~mol}^{-1}\right)}{\text { density }\left(\mathrm{g} \mathrm{~cm}^{-3}\right)}

The table gives the atomic volumes of the first nineteen elements, in the form in which they occur at STP.

Key:

Key:

Question 1(c)

(a)

Suggest why some elements, such as carbon and oxygen, have more than one value for their atomic volume.

[ 1 ]

Question 1

[Maximum number: 2]

Ethane-1,2-diol, HOCH2CH2OH\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{OH}, has a wide variety of uses including the removal of ice from aircraft and heat transfer in a solar cell.

Question 1(d)

(a)

Explain why the boiling point of ethane-1,2-diol is significantly greater than that of ethene.

[ 2 ]

Question 1

[Maximum number: 3]

Ammonium nitrate, NH4NO3\mathrm{NH}_{4} \mathrm{NO}_{3}, is used as a high nitrogen fertilizer.

Question 1(f)

(a)

Solid ammonium nitrate can decompose to gaseous dinitrogen monoxide and liquid water.

[ 3 ]

Question 1(f)(v)

(i)

Deduce the Lewis (electron dot) structure, including formal charges, and shape for dinitrogen monoxide showing nitrogen as the central atom.

Lewis structure:

Shape:

[ 3 ]

Question 1

[Maximum number: 2]

A class studied the equilibrium established when ethanoic acid and ethanol react together in the presence of a strong acid, using propanone as an inert solvent. The equation is given below.

CH3COOH+C2H5OH⇌CH3COOC2H5+H2O\mathrm{CH}_{3} \mathrm{COOH}+\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH} \rightleftharpoons \mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}_{5}+\mathrm{H}_{2} \mathrm{O}

One group made the following initial mixture:

Table

Question 1(g)

(a)

Propanone is used as the solvent because one compound involved in the equilibrium is insoluble in water. Identify this compound and explain why it is insoluble in water.

[ 2 ]

Question 1

[Maximum number: 1]

Chlorine undergoes many reactions.

Question 1(d)

Question 1(d)(ii)

(a)
(i)

Predict, giving a reason, whether ethane or chloroethane is more reactive.

[ 1 ]

Question 1

[Maximum number: 1]

Water contaminated with mercury contains methylmercury ions, CH3Hg+\mathrm{CH}_{3} \mathrm{Hg}^{+}. These ions are absorbed by living organisms, then slowly metabolized and excreted.

Young fish were taken at regular intervals from a mercury contaminated lake and tested to determine mercury ion content.

Mercury ion content in muscle tissue of fish

Mercury ion content in muscle tissue of fish

Question 1(a)

Question 1(a)(iii)

(a)
(i)

State why CH3Hg+\mathrm{CH}_{3} \mathrm{Hg}^{+}is more likely to be absorbed by fish than mercury, Hg .

[ 1 ]

Question 1

[Maximum number: 9]

Hydrogen cyanide, HCN , is a very toxic compound.

Question 1(a)

(a)

Pure HCN is a volatile liquid, boiling at 26∘C26^{\circ} \mathrm{C}.

[ 8 ]

Question 1(a)(i)

(i)

Draw the Lewis formula of the HCN molecule.

[ 1 ]

Question 1(a)(ii)

(ii)

Deduce the hybridization of the carbon atom and the number of sigma and pi bonds that it forms.

Hybridization:
Sigma bonds:
Pi bonds:

[ 2 ]

Question 1(a)(iii)

(iii)

State and explain the molecular geometry of HCN without referring to hybridization.

Molecular geometry:
Explanation:

[ 2 ]

Question 1(a)(iv)

(iv)

HCN is a polar molecule. Deduce which atom carries a partial positive charge and which carries a partial negative charge.

Partial positive charge:
Partial negative charge:

[ 1 ]

Question 1(a)(v)

(v)

Explain why nitrogen gas, N2\mathrm{N}_{2}, has a much lower boiling point than HCN .

[ 2 ]

Question 1(c)

(b)

The cyanide ion, CN−\mathrm{CN}^{-}, can form complex ions, such as [Fe(CN)6]4−\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{4-}.

[ 1 ]

Question 1(c)(i)

(i)

State the precise type of bond formation between the cyanide ion and the iron ion.
bond

[ 1 ]

Question 1

[Maximum number: 2]

Alkanes are commonly occurring organic compounds.

Question 1(a)

(a)

The first four straight chain alkanes are gases at room temperature.

Boiling points of straight chain alkanes

Boiling points of straight chain alkanes

[ 2 ]

Question 1(a)(i)

(i)

Explain why the boiling point increases from methane to propane.

[ 2 ]

Question 1

[Maximum number: 2]

The absorption of infrared (IR) radiation by molecules in the atmosphere affects global temperatures.

Graph of IR absorbances for oxygen and ozone molecules

Graph of IR absorbances for oxygen and ozone molecules

Question 1(b)

(a)

The following data has been compiled for a range of molecules that may be found in the atmosphere.

Table
[ 2 ]

Question 1(b)(ii)

(i)

Explain the increase in molecular dipole moment as one chlorine atom in CCl4\mathrm{CCl}_{4} is replaced with fluorine to produce CCl3 F\mathrm{CCl}_{3} \mathrm{~F}.

[ 2 ]
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