Nanyang Junior College H2/H1 Chemistry JC1 2014
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Name: _________________________________ CT: ___________ Date:
__________
Section C: Assignment (15 marks) Take no more than 25 min to
complete this assignment.
1 Nitrate, NO3-, and phosphate, PO43-, are oxoanions of nitrogen
and phosphorus respectively.
a) Draw dot-and-cross diagrams to show the bonding in NO3- and
PO43-. Hence, deduce the shapes and state the bond angles around
the nitrogen and phosphorus atom. [4]
[1] [1] Trigonal planar, 120 [1] Tetrahedral, 109 [1]
b) Explain why it is not possible for nitrogen to form an
oxoanion with a formula of NO43-. [1] Nitrogen has no empty and
energetically accessible 3d orbitals to expand its octet.
2 This question is on the properties of halogens and their
compounds.
a) Halogens like Cl2 and I2 are soluble in the non-polar solvent
CCl4. However, the interhalogen compound, ICl, is insoluble in
CCl4. Explain why. [2]
Cl2 and I2 are soluble in CCl4 as they can form van der Waals
interactions with CCl4. [1]
ICl is insoluble in CCl4 as the energy released during the
formation of vdW interactions with ICl is not enough to overcome
the permanent dipole permanent dipole interactions between ICl
molecules (and vdW forces between CCl4 molecules). [1]
The hydrogen halides undergo thermal decomposition according to
the following equation.
2HX H2 + X2 (where X represents the halogen)
b) Why is the rate of thermal decomposition of hydrogen fluoride
slower than that of hydrogen iodide? [2] The bond energy of HF is
larger than that of HI. This is because the HF bond is shorter than
the HI bond. [1] There is less degree of orbital overlap and less
energy is required to break the bond. [1]
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Nanyang Junior College H2/H1 Chemistry JC1 2014
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3 Ethanoic acid, CH3COOH, is the main component of vinegar.
a) Explain, with illustrations, why ethanoic acid is soluble in
water. [2]
Soluble as they can form hydrogen bonds with water [1] Drawing
showing at least 1 H-bond (with +, -, lone pairs, hash lines)
[1]
b) Ethanoic acid (Mr = 60.0) is a liquid while magnesium
fluoride (Mr = 62) is a solid at r.t.p. Explain. [2]
Ethanoic acid has simple molecular structure with hydrogen bonds
between molecules. Magnesium fluoride has giant ionic lattice with
Mg2+ and F- ions held together by strong ionic bonds. [1] More
energy is required to overcome the stronger ionic bond so MgF2 has
a higher melting point and is a solid at rtp, while ethanoic acid
is a liquid. [1]
c) Ethanoic acid undergoes neutralisation with sodium hydroxide
to form sodium ethanoate.
CH3COOH + NaOH CH3COO-Na+ + H2O
Is sodium ethanoate soluble in water? Draw a diagram to explain.
[2]
Soluble. Sodium ethanoate dissociates into its ions in water.
These ions can form ion-dipole interactions with water. [1]
[1]
PS3: What are the points to note
when drawing the interactions?
PS3: Structure, bonding,
particles? Compare forces, link to
energy and bp.
