Balance the following redox equation under acidic aqueous conditions. What is the coefficient of water in the balanced equation?

NO₃^– + I^– → IO₃^– + NO₂

When borane gas (BH₃(g)) is bubbled through water, the solution it forms is acidic. However this acidity does not come from hydrogens on the BH₃ molecule. 

Explain this phenomenon in no more than 3 sentences. (Hint: refer to the different theories of acids and bases learnt this term) [3 marks]

With reference to the diagram below and using the theory covered in this course, describe how soap works to remove dirt from human skin.

• Buffers are added to foods and beverages to modify flavours and preserve them.
• Cola drinks include phosphoric acid and carbonic acid (from dissolved CO₂) that lower the pH of the drink and produce buffer systems.
• The primary buffer system that determines the pH of cola drinks is the phosphoric acid:dihydrogen phosphate (H₃PO₄/H₂PO₄^-; pK _a H₃PO₄ = 2.16) buffer system.

1. The results show that the drinks Coca Cola and Pepsi Cola have very similar pH values (2.7 and 2.5 respectively)., what does this imply about the composition of their buffer systems? [1 mark]

2. For the Coca Cola drink 5.19 mL of 0.05 M NaOH was required to raise the pH by 1.0. However, for the Pepsi Cola drink 6.35 mL of 0.05 M NaOH was required to raise the pH by 1.0. Explain this observation, accounting for your response to the question above and the fact that both cola drinks have the same buffer system. [3 marks]

The side chains of amino acids are responsible for giving proteins their secondary and tertiary structure (they control the way the proteins fold). The two amino acids above are largely responsible for producing the protein structures known as α-helices. However, these structures are very sensitive to the pH of the solution in which the protein is suspended. Explain why these structures are particularly sensitive to pH.

In your own words explain how a substance can exist as a vapour  and has a vapour pressure despite being at a temperature that is below the substance's boiling point.  [5 marks]

Your answer should refer to the theory covered in the course and be 4-5 sentences in length.

Of the two gases, nitrogen (N₂) and carbon dioxide (CO₂), which one do you expect would deviate the most from ideal gas behaviour at low temperatures? Justify your answer. 

Explain why buffer potential is maximised at the pH that matches the pKa of the weak acid of the buffer. What does this have to do with buffer capacity?

By referring to the concept of electronegativity and bonding types, why is sodium chloride a solid at 25 °C and atmospheric pressure, whereas nitrogen (N₂) is a gas?