1 This question is about the chemistry of compounds containing phosphorus.
Phosphorus forms several acids including H3PO4 and H3PO3.
H3PO4 is a tribasic acid. The equilibria for the dissociations are shown below.
1 H3PO4 ⇌ H+ + H2PO4–
2 H2PO4– ⇌ H+ + HPO42–
3 HPO42– ⇌ H+ + PO43–
i. During the equilibria, H2PO4– behaves both as an acid and as a base.
Explain this statement, using the equilibria 1, 2 and 3, as required.
[2]
ii. In a H3PO3 molecule, the O atoms are covalently bonded to the P atom. The H atoms are bonded to the O
atoms.
Draw the structure of a H3PO3 molecule, showing all the bonds.
On your diagram, add the values for the O–P–O and P–O–H bond angles.
[3]
iii. The systematic name of H3PO4 is phosphoric(V) acid.
What is the systematic name of H3PO3?
[1]
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, 2 Hydrogen reacts much more readily with alkenes than with alkanes.
Why is this?
A Alkenes are polar molecules whereas alkanes are not.
B All atoms in an alkane have a full outer shell of electrons.
C The bond enthalpy of C–C σ bonds is higher than that of π bonds.
D The bond enthalpy of C–C σ bonds is lower than that of π bonds.
Your answer [1]
3 Short-chain carboxylic acids, such as methanoic acid, HCOOH, are soluble in water.
Explain, with a labelled diagram, how HCOOH interacts with water when it dissolves.
[2]
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, 4 The structure of but-1-ene is shown below.
Which row has the correct shape around carbon atoms labelled x and y?
x y
A Tetrahedral Pyramidal
B Trigonal planar Tetrahedral
C Trigonal planar Pyramidal
D Pyramidal Tetrahedral
Your answer [1]
5 All organic compounds have covalent bonds.
What is the electrostatic attraction in a covalent bond between?
A A shared pair of electrons and the nuclei of the bonded atoms
B Cations and delocalised electrons
C Oppositely charged ions
D Two molecules
Your answer [1]
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, 6 This question is about covalent compounds of nitrogen.
Hydrogen cyanide, HCN, is bonded by a single bond between the H and C atoms and a triple bond between the
C and N atoms.
Draw a ‘dot-and-cross’ diagram for a molecule of HCN.
Use different symbols for electrons from H, C and N.
Show outer electrons only.
[2]
7(a) This question is about hydrocarbons.
The skeletal formulae and boiling points of three isomers of C6H14 are shown in the table below.
Isomer Molecular formula Skeletal formula Boiling point/°C
A C6H14 69
B C6H14 63
C C6H14 58
State and explain the trend in the boiling points shown in the table.
Refer to the isomers A, B and C in your answer.
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Phosphorus forms several acids including H3PO4 and H3PO3.
H3PO4 is a tribasic acid. The equilibria for the dissociations are shown below.
1 H3PO4 ⇌ H+ + H2PO4–
2 H2PO4– ⇌ H+ + HPO42–
3 HPO42– ⇌ H+ + PO43–
i. During the equilibria, H2PO4– behaves both as an acid and as a base.
Explain this statement, using the equilibria 1, 2 and 3, as required.
[2]
ii. In a H3PO3 molecule, the O atoms are covalently bonded to the P atom. The H atoms are bonded to the O
atoms.
Draw the structure of a H3PO3 molecule, showing all the bonds.
On your diagram, add the values for the O–P–O and P–O–H bond angles.
[3]
iii. The systematic name of H3PO4 is phosphoric(V) acid.
What is the systematic name of H3PO3?
[1]
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, 2 Hydrogen reacts much more readily with alkenes than with alkanes.
Why is this?
A Alkenes are polar molecules whereas alkanes are not.
B All atoms in an alkane have a full outer shell of electrons.
C The bond enthalpy of C–C σ bonds is higher than that of π bonds.
D The bond enthalpy of C–C σ bonds is lower than that of π bonds.
Your answer [1]
3 Short-chain carboxylic acids, such as methanoic acid, HCOOH, are soluble in water.
Explain, with a labelled diagram, how HCOOH interacts with water when it dissolves.
[2]
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, 4 The structure of but-1-ene is shown below.
Which row has the correct shape around carbon atoms labelled x and y?
x y
A Tetrahedral Pyramidal
B Trigonal planar Tetrahedral
C Trigonal planar Pyramidal
D Pyramidal Tetrahedral
Your answer [1]
5 All organic compounds have covalent bonds.
What is the electrostatic attraction in a covalent bond between?
A A shared pair of electrons and the nuclei of the bonded atoms
B Cations and delocalised electrons
C Oppositely charged ions
D Two molecules
Your answer [1]
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, 6 This question is about covalent compounds of nitrogen.
Hydrogen cyanide, HCN, is bonded by a single bond between the H and C atoms and a triple bond between the
C and N atoms.
Draw a ‘dot-and-cross’ diagram for a molecule of HCN.
Use different symbols for electrons from H, C and N.
Show outer electrons only.
[2]
7(a) This question is about hydrocarbons.
The skeletal formulae and boiling points of three isomers of C6H14 are shown in the table below.
Isomer Molecular formula Skeletal formula Boiling point/°C
A C6H14 69
B C6H14 63
C C6H14 58
State and explain the trend in the boiling points shown in the table.
Refer to the isomers A, B and C in your answer.
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