11A - Obtaining Rate Data Flashcards
What property of a substance is often used to measure the rate of a chemical reaction in the lab?
The property used to measure the rate of a reaction is often related to a change in concentration and can include colour, mass, volume, or other observable characteristics.
What instrument is used to measure the amount of light that passes through a solution to monitor colour changes in a reaction?
A colorimeter is used to measure the amount of light passing through a solution to monitor colour changes during a reaction.
Why is colorimetry not suitable for monitoring the formation of coloured precipitates in a reaction?
Because the light will be scattered or blocked by the precipitate.
How is the mass loss used to measure the rate of a reaction when a gas is produced?
When a gas is produced in a reaction, its mass loss can be used to measure the rate of reaction. The change in mass over time is plotted, providing a measure of the amount of reactant.
What is one limitation of using mass loss to measure the rate of reaction in the presence of gases?
One limitation is that the gas must be sufficiently dense for its change in mass to be measurable, making it unsuitable for gases like hydrogen with a low molar mass.
How can the volume of gas produced in a reaction be measured to determine the rate of the reaction?
The volume of gas produced in a reaction can be trapped and measured over time to determine the rate of the reaction. The volume varies with time and represents the amount of product.
Why is measuring concentration changes during a reaction not easy, and what is often a more convenient approach?
Measuring concentration changes can be challenging as it may affect the rate of reaction. Often, it is more convenient to ‘stop the clock’ when a specific, visible point in the reaction is reached, as in the case of quenching a reaction.
What is an example of a reaction where monitoring concentration changes using a visible point is common in experiments?
An example is the reaction between sodium thiosulfate and hydrochloric acid, which slowly produces a yellow precipitate of sulfur that obscures a cross when viewed through the solution.
Na2S2O3 (aq) + 2HCl (aq) → 2NaCl aq) + SO2 (g) + H2O (l) + S(s)
What limitation is associated with using a visible point to measure the rate of reaction in experiments?
A limitation is that often, this method generates only one piece of data for analysis.
How can you interpret graphs of changes in concentration, volume, or mass against time?
By calculating rates from tangents to the graph to understand the rate of reaction.
