Concentration and rate: practical using end point method
Lesson details
Learning outcome
I can carry out a fair test to investigate how the rate of reaction depends on the concentration of a reacting solution.
Key learning points
- The reaction between sodium thiosulfate solution and hydrochloric acid produces a cloudy precipitate.
- At the end point of the disappearing cross experiment, each reaction has produced the same amount of product.
- At the end point of the disappearing cross experiment, the chemical reaction may not be complete.
- Increasing concentration of a reacting solution introduces more reactant particles, so they collide more frequently.
Keywords
Rate of reaction - Rate of reaction is the speed with which a chemical reaction takes place.
End point method - An end point method is used to measure the progress of a reaction until it has reached completion or a desired point e.g. a colour change.
Precipitate - A precipitate is an insoluble solid formed when two solutions react together.
Fair test - In a fair test variables are controlled so that only one change affects the dependent variable.
Common misconception
The reaction stops when the 'X' is no longer visible.
The disappearance of the cross only indicates that the sulfur precipitate has formed sufficiently to obscure the cross. The reaction itself continues beyond this point until all reactants are consumed.
Teacher tip
Pupils could dilute the sodium thiosulfate themselves to produce three different concentrations. See the additional material for additional guidance.
Equipment
Conical flask, card marked with an 'X', measuring cylinders, different concentrations of sodium thiosulfate, hydrochloric acid, timer and eye protection.
Content guidance
Risk assessment required - equipment
Supervision
Adult supervision required
Licence
Lesson video
Loading...
Prior knowledge starter quiz
6 Questions
Q1.Which of the following statements about concentration and rate of reaction is correct?
Q2.What effect does concentration have on the rate of reaction?
Q3.Which of the following methods is used when we measure the progress of a reaction until it has reached a desired point?
Q4.Which variable is the independent variable in an experiment where we change the concentration and measure the time taken for a colour change to occur?
Q5.Which variable is the dependent variable in an experiment where we change the concentration and measure the time taken for a colour change to occur?
Q6.What is the main reason for repeating a rate of reaction experiment multiple times?
Assessment exit quiz
6 Questions
Q1.In the disappearing cross experiment, which of the following indicates the end point of the reaction?
Q2.Which of the following is observed when sodium thiosulfate reacts with hydrochloric acid?
Q3.When sodium thiosulfate and hydrochloric acid react together, a yellow precipitate of sulfur forms. In which state is this sulfur?
Q4.Increasing the concentration of reactants introduces more...
Q5.Which statement about the amount of product formed at the end point of the disappearing cross experiment, when using different concentrations of sodium thiosulfate in excess, is correct?
Q6.At the end point of a reaction, the reaction may not be complete because ...
To help you plan your 11 combined science lesson on: Concentration and rate: practical using end point method, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your 11 combined science lesson on: Concentration and rate: practical using end point method, download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
We use learning cycles to break down learning into key concepts or ideas linked to the learning outcome. Each learning cycle features explanations with checks for understanding and practice tasks with feedback. All of this is found in our slide decks, ready for you to download and edit. The practice tasks are also available as printable worksheets and some lessons have additional materials with extra material you might need for teaching the lesson.
The assessment exit quiz will test your pupils' understanding of the key learning points.
Our video is a tool for planning, showing how other teachers might teach the lesson, offering helpful tips, modelled explanations and inspiration for your own delivery in the classroom. Plus, you can set it as homework or revision for pupils and keep their learning on track by sharing an online pupil version of this lesson.
Explore more key stage 4 combined science lessons from the Rate of reaction unit, dive into the full secondary combined science curriculum, or learn more about lesson planning.