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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⁻¹, rather than kJ mol⁻¹. b. Hydrogen gas is bubbled... 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
a. Food chemists quote the energy content of food in kJ g⁻¹, rather than kJ mol⁻¹.
Answer
Food chemists emphasize the energy content in kJ g⁻¹ because it provides a more practical measurement for the portion sizes typically consumed. Most foods are not pure substances, and their molecular composition varies significantly. Therefore, using kJ mol⁻¹ would complicate the understanding of energy intake since it would require knowledge of the molar mass of each food item consumed.
Step 2
b. Hydrogen gas is bubbled through a solution of 1.0 M Fe²⁺(aq) ions.
Answer
Although the electrochemical series predicts that a redox reaction could take place with hydrogen gas in the presence of Fe²⁺ ions, no reaction occurs at room temperature due to the activation energy barrier. The reaction is too slow at this temperature, suggesting that the conditions (like temperature or concentration) are not suitable for the reaction to proceed despite the theoretical prediction.
Step 3
c. The oxidation state of iron, in its compounds, is normally either +2 or +3.
Answer
Iron, as a transition metal, can exhibit multiple oxidation states due to its ability to lose electrons from both the 4s and 3d subshells. However, in its most common oxidation states (+2 or +3), iron typically loses two or three electrons respectively. In contrast, calcium only exhibits a +2 oxidation state, as it loses two electrons from its outer 4s subshell, making its behavior more predictable in compound formation.