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Give concise explanations for each of the following - VCE - SSCE Chemistry - Question 6 - 2005 - Paper 1
Question 6
Give concise explanations for each of the following. a. Food chemists quote the energy content of food in kJ g<sup>-1</sup>, rather than kJ mol<sup>-1</sup>. b. Hy... show full transcript
Worked Solution & Example Answer:Give concise explanations for each of the following - VCE - SSCE Chemistry - Question 6 - 2005 - Paper 1
Step 1
Food chemists quote the energy content of food in kJ g<sup>-1</sup>, rather than kJ mol<sup>-1</sup>.
Answer
Food chemists prefer to use kJ g<sup>-1</sup> because it allows for a more direct understanding of the energy content relative to the mass of the food. Most foods are consumed in grams rather than moles, making kJ g<sup>-1</sup> a more practical measure. The mole is a unit that applies to chemical quantities, and since food is primarily made up of various compounds and not pure substances, utilizing mass-based energy content simplifies dietary considerations.
Step 2
Hydrogen gas is bubbled through a solution of 1.0 M Fe<sup>2+</sup>(aq) ions. On the basis of the electrochemical series, a redox reaction is predicted to occur. In practice, no reaction occurs at room temperature.
Answer
According to the electrochemical series, hydrogen is less reactive than Fe<sup>2+</sup>, implying that a redox reaction could occur where Fe<sup>2+</sup> ions are reduced to metallic iron, and hydrogen is oxidized. However, under normal conditions, the reaction may not proceed at room temperature due to a high activation energy barrier, leading to no observable reaction. Additionally, the standard electrode potential of hydrogen may assist in explaining the lack of reactivity under these conditions.
Step 3
The oxidation state of iron, in its compounds, is normally either +2 or +3, whereas that of calcium, in its compounds, is +2 only.
Answer
Iron is a transition metal that can exhibit multiple oxidation states due to its ability to lose electrons from both the 4s and 3d subshells. Consequently, iron commonly exists in oxidation states of +2 (ferrous) and +3 (ferric). Conversely, calcium, being an alkaline earth metal, typically has a fixed oxidation state of +2, as it loses the two 4s electrons easily and does not have available d electrons that it can use in bonding.