A student is investigating the rate of the reaction between acidified potassium permanganate ($KMnO_4$) and oxalic acid ($H_2C_2O_4$). The student monitors the reaction progress by measuring the absorbance of the solution using a spectrophotometer at a specific wavelength over time. Which of the following identifies a significant limitation of using this method to determine the instantaneous rate of reaction at a specific point?
The spectrophotometer may not be sensitive enough to detect small changes in absorbance at low concentrations of $KMnO_4$.
The time taken to obtain an absorbance reading introduces a delay, meaning the measured absorbance reflects an average rate over that time interval, not the instantaneous rate.
The color of the solution may change due to the formation of intermediate species that also absorb at the selected wavelength.
The reaction may be affected by changes in temperature during the measurement, influencing the rate of reaction.
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Create Free Account Log inThis is a free VCE Units 3 & 4 Chemistry practice question worth 1 mark, testing your understanding of Investigation limits. It falls under Student-designed scientific investigation in Unit 4: How are carbon-based compounds designed for purpose?. Submit your answer above to receive instant AI-powered marking and personalised feedback.
Carbon is the basis not only of the structure of living tissues but is also found in fuels, foods, medicines, polymers and many other materials that we use in everyday life. In this unit students investigate the structures and reactions of carbon-based organic compounds, including considering how green chemistry principles are applied in the production of synthetic organic compounds. They study the metabolism of food and the action of medicines in the body. They explore how laboratory analysis and various instrumentation techniques can be applied to analyse organic compounds in order to identify them and to ensure product purity. Students conduct practical investigations related to the synthesis and analysis of organic compounds, involving reaction pathways, organic synthesis, identification of functional groups, direct redox titrations, solvent extraction and distillations. Throughout the unit students use chemistry terminology including symbols, formulas, chemical nomenclature and equations to represent and explain observations and data from their own investigations and to evaluate the chemistry-based claims of others. A student-designed scientific investigation involving the generation of primary data related to the production of energy and/or chemicals and/or the analysis or synthesis of organic compounds is undertaken in either Unit 3 or Unit 4, or across both Units 3 and 4, and is assessed in Unit 4 Outcome 3. The design, analysis and findings of the investigation are presented in a scientific poster format. School-based assessment The student’s level of achievement in Unit 4 will be determined by School-assessed Coursework, which contributes 30 per cent to the study score. Students complete a set of tasks to address Outcomes 1 and 2, and design and conduct a student investigation for Outcome 3. External assessment The level of achievement for Units 3 and 4 is also assessed by an end-of-year examination contributing 50 per cent to the study score.
Students undertake a student-designed scientific investigation in either Unit 3 or Unit 4, or across both Units 3 and 4. The investigation involves the generation of primary data related to the production of energy and/or chemicals and/or the analysis or synthesis of organic compounds. The design, analysis and findings are presented in a scientific poster. Outcome 3 On completion of this unit the student should be able to design and conduct a scientific investigation related to the production of energy and/or chemicals and/or the analysis or synthesis of organic compounds, and present an aim, methodology and method, results, discussion and conclusion in a scientific poster. Key knowledge
the limitations of investigation methodologies and methods, and of data generation and/or analysis
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