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Questions and Answers
What technique can be utilized to monitor the change in concentration of a reactant over time during a reaction?
Titration.
How can the rate of a reaction involving gas production be measured?
By measuring the volume of gas produced over time.
In the context of reaction rates, what is a calibration curve used for in colorimetry?
It is used to convert absorbance readings into concentration values.
Describe the relationship between the absorption of light and concentration in a colorimetry experiment.
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What observation indicates the consumption of iodine during the iodination of propanone?
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What is the significance of plotting a mass-time graph in a reaction that produces a gas?
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Explain how a gas syringe can provide information about the rate of reaction.
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What does titration reveal about a reaction mixture at regular intervals?
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What is the significance of measuring reactant concentration over time in determining the rate of a reaction?
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How does the order of a reaction affect the half-life of a first order reactant?
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Describe how gas volume measurements can be used to track the progress of a reaction.
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Explain the role of colorimetry and calibration in determining the rate of a chemical reaction.
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What experimental techniques could be utilized to investigate the rate dependence on reactant concentration?
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What is the role of the rate-determining step in a multi-step reaction mechanism?
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How can mass change method be applied to measure reaction rates?
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Why might one choose to measure changes in product concentration rather than reactant concentration when studying reaction rates?
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What is the significance of the weak acid concentration compared to the concentration of H+ ions in calculations for weak acids?
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Describe the role of a buffer solution in maintaining pH stability.
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How does the addition of a small amount of base affect the equilibrium in the NH3 and NH4+ buffer system?
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What is the significance of the equilibrium constant, Ka, in acid-base chemistry?
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In the hypothetical equilibrium reaction HA ⇌ A- + H+, what does 'x' represent?
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Explain why the approximation [HA]equilibrium ~ [A-]equilibrium is valid for weak acids.
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What happens to pH when a strong base is added to a buffer solution containing a weak acid?
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Define the term 'reservoir' in the context of buffer solutions.
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Study Notes
Mass Change
- The mass of the reaction mixture decreases as the reaction proceeds when a gas is produced.
- The rate can be determined by plotting a mass-time graph and drawing a tangent to the curve.
Volume of Gas Evolved
- This method can be used to determine the rate of reaction when a gas is produced.
- Measure the volume of gas produced over the course of the reaction.
- Plot a graph of volume evolved against time.
- A gas syringe or an underwater upside down measuring cylinder can be used to collect the gas.
Titration
- Small samples of a reaction mixture are removed at regular intervals.
- These samples are titrated to determine the concentration of a given reactant or product at that time.
- A concentration-time graph can be plotted.
Colorimetry
- This method can be used to determine the rate of reaction for a reaction that involves the formation or depletion of a coloured species.
- A colorimeter measures the amount of light that is absorbed by a solution.
- The amount of light absorbed is proportional to the concentration of the coloured species.
- A calibration curve is often generated in a colorimetry experiment.
Half-life
- Half-life (t1/2): The time taken for the initial concentration of the reactants to decrease by half.
- It can be found from a concentration-time graph.
- The overall order of a reaction affects how the length of the half-life changes over the course of a reaction.
First Order Reaction
- In a first order reaction, the half-life of a reaction is constant throughout the reaction.
- The time taken for the reactant concentration to go from 100% to 50% is the same as the time taken for the reactant concentration to go from 50% to 25%, and so on.
Experimental Techniques
- There are various techniques to obtain rate data for reactions.
- The two general ways to investigate reaction rates are:
- By measuring the change in a reactant mass or concentration over time.
- By measuring the change in a product mass or concentration over time.
- Collecting raw data generates a concentration-time graph, mass-time graph or volume-time graph, which can then be used to calculate the rate of reaction.
- To find reactant orders and the overall order of reaction, the concentration of reactants can be varied and their effects on the rate of reaction can be analyzed.
Buffer Action
- A buffer solution is a system that minimizes pH changes on addition of small amounts of an acid or a base.
- It is formed from a weak acid and its salt or an excess of a weak acid and a strong alkali.
- This produces a mixture containing H+ ions and a large reservoir of OH- ions which helps to resist any change in pH.
- Therefore, a buffer solution is defined as: A solution which is able to resist changes in pH when small volumes of acid or base are added.
- The large reservoir of OH- ions allows the ratio of acid to base in the mixture to be kept almost constant.
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Description
Explore various methods used to measure the rate of chemical reactions, including mass change, gas volume, titration, and colorimetry. Understand how each technique can provide insights into reaction kinetics. This quiz covers essential concepts in chemistry related to rate measurement.