[Maximum number: 4]

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

(a)

Draw the Lewis (electron dot) structure of methanoic acid.

[ 1 ]

(b)

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

[ 3 ]

(i)

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

[ 2 ]

(ii)

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

[ 1 ]

[Maximum number: 5]

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

(a)

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

[ 3 ]

(i)

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

[ 2 ]

(ii)

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

[ 1 ]

(b)

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

[ 2 ]

(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 ]

[Maximum number: 1]

Water contaminated with mercury contains methylmercury ions, $\mathrm{CH}_{3} \mathrm{Hg}^{+}$ . 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

(a)

(i)

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

[ 1 ]

[Maximum number: 2]

Alkanes are commonly occurring organic compounds.

(a)

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

Boiling points of straight chain alkanes

[ 2 ]

(i)

Explain why the boiling point increases from methane to propane.

[ 2 ]

[Maximum number: 1]

Water contaminated with mercury contains methylmercury ions, $\mathrm{CH}_{3} \mathrm{Hg}^{+}$ . 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

(a)

(i)

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

[ 1 ]

[Maximum number: 2]

Alkanes are commonly occurring organic compounds.

(a)

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

Boiling points of straight chain alkanes

[ 2 ]

(i)

Explain why the boiling point increases from methane to propane.

[ 2 ]

[Maximum number: 5]

Phosphorus is an element that is an essential part of the biological molecules involved in both respiration and photosynthesis.

(a)

7.75 g of phosphorus was combusted in a limited supply of oxygen, the mass of the oxide produced was 13.75 g .

[ 2 ]

(i)

Describe the nature of the bond between oxygen and phosphorus. Use sections 9 and 17 of the data booklet.

[ 2 ]

(b)

Another compound of phosphorus is phosphine, $\mathrm{PH}_{3}$ , it forms a phosphonium ion, $\mathrm{PH}_{4}^{+}$ .

State the types of bonds present in the phosphonium ion, $\mathrm{PH}_{4}{ }^{+}$ , and explain how these bonds are formed.

[ 2 ]

(c)

Phosphorus trichloride, $\mathrm{PCl}_{3}$ , is a common compound of phosphorus.

Deduce the Lewis formula of $\mathrm{PCl}_{3}$ .

[ 1 ]

[Maximum number: 6]

Hydrogen cyanide, HCN , is a very toxic compound.

(a)

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

[ 6 ]

(i)

Draw the Lewis formula of the HCN molecule.

[ 1 ]

(ii)

State and explain the molecular geometry of HCN .

Molecular geometry:
Explanation:

[ 2 ]

(iii)

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 ]

(iv)

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

[ 2 ]

[Maximum number: 6]

Phosphorus is an element that is an essential part of the biological molecules involved in both respiration and photosynthesis.

(a)

7.75 g of phosphorus was combusted in a limited supply of oxygen, the mass of the oxide produced was 13.75 g .

[ 2 ]

(i)

Describe the nature of the bond between oxygen and phosphorus. Use sections 9 and 17 of the data booklet.

[ 2 ]

(b)

Phosphorus has two chlorides, phosphorus(III) chloride, $\mathrm{PCl}_{3}$ , and phosphorus(V) chloride, $\mathrm{PCl}_{5}$ .

[ 4 ]

(i)

Deduce the Lewis formula of $\mathrm{PCl}_{3}$ .

[ 1 ]

(ii)

Deduce the molecular geometry of $\mathrm{PCl}_{3}$ and $\mathrm{PCl}_{5}$ .
$\mathrm{PCl}_{3}:$

$\mathrm{PCl}_{5}$ :

[ 2 ]

(iii)

Suggest a value for the bond angle in $\mathrm{PCl}_{3}$ .

[ 1 ]

[Maximum number: 9]

Hydrogen cyanide, HCN , is a very toxic compound.

(a)

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

[ 8 ]

(i)

Draw the Lewis formula of the HCN molecule.

[ 1 ]

(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 ]

(iii)

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

Molecular geometry:
Explanation:

[ 2 ]

(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 ]

(v)

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

[ 2 ]

(b)

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

[ 1 ]

(i)

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

[ 1 ]