Required Practical 5 - Rates of Reaction

What are three ways of measuring the rate of a reaction?

Observe how quickly a precipitate forms, measure the change in mass, or measure the volume of gas given off

How is rate of reaction calculated?

Rate = amount of product formed or reactant used ÷ time

How can rate be measured if a precipitate is produced?

Place paper with a black cross under the flask and measure the time for the cross to disappear

How can rate be measured if a coloured reactant forms a colourless solution?

Time how long it takes for the solution to become colourless

Why is the precipitate or colour change experiment unreliable?

It’s subjective since different people may judge the colour change or disappearance point differently

How can rate be measured when there is a change in mass?

Place the flask on a balance and record mass loss at regular intervals as gas is produced

How can rate be measured when a gas is given off?

Attach a gas syringe to the flask and record the gas volume at regular intervals

How can the rate of reaction after 30 seconds be found?

Plot a graph of product formed or reactant used vs time, draw a tangent at 30 seconds, and calculate its gradient

What are the units of rate of reaction when measuring mass change?

g/s

What are the units of rate of reaction when measuring gas volume?

cm³/s

How could you investigate how HCl concentration affects the rate when magnesium is added?

Add magnesium to HCl in a flask connected to a gas syringe, measure gas volume every 10 seconds, and repeat with different acid concentrations

How could you investigate how sodium thiosulfate concentration affects rate when reacted with HCl?

Add sodium thiosulfate and HCl in a flask over a paper cross, time how long for the cross to disappear, and repeat with different concentrations