Starter quiz
- Which of the following statements about concentration and rate of reaction is correct?
- Concentration and rate of reaction are directly proportional. ✓
- Concentration and rate of reaction are inversely proportional.
- Concentration has no effect on the rate of reaction.
- Only high concentrations affect the rate of reaction.
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- What effect does concentration have on the rate of reaction?
- Doubling the concentration of a reacting solution doubles the rate of reaction. ✓
- Doubling the concentration of a reacting solution halves the rate of reaction.
- Halving the concentration of a reacting solution doubles the rate of reaction.
- Halving the concentration of a reacting solution halves the rate of reaction. ✓
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- Which of the following methods is used when we measure the progress of a reaction until it has reached a desired point?
- gas collection
- calorimetry
- neutralisation
- end point ✓
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- 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?
- the concentration of a reacting solution ✓
- the temperature of the reactants
- the time taken for the colour change
- the volume of reacting solutions
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- 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?
- the concentration of reacting solutions
- the temperature of the reactants
- the time taken for the colour change ✓
- the volume of reacting solutions
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- What is the main reason for repeating a rate of reaction experiment multiple times?
- to increase the rate of reaction
- to decrease the rate of reaction
- to change the dependent variable
- to adjust control variables
- to obtain more reliable results ✓
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Exit quiz
- In the disappearing cross experiment, which of the following indicates the end point of the reaction?
- the solution turns blue
- the solution becomes colourless
- an X placed under the reaction mixture is no longer visible ✓
- the solution starts to bubble
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- Which of the following is observed when sodium thiosulfate reacts with hydrochloric acid?
- a colour change from blue to red
- the reaction mixture changes from clear to cloudy ✓
- light is emitted
- no visible change
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- When sodium thiosulfate and hydrochloric acid react together, a yellow precipitate of sulfur forms. In which state is this sulfur?
- solid ✓
- liquid
- gas
- aqueous
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- Increasing the concentration of reactants introduces more...
- solvent particles.
- product particles.
- reactant particles. ✓
- inert particles.
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- 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?
- a higher concentration produces a larger amount of product
- a lower concentration produces a larger amount of product
- the different concentrations produce different products
- the different concentrations produce the same amount of product ✓
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- At the end point of a reaction, the reaction may not be complete because ...
- all the reactants have been converted to products.
- some of the reactants have not yet reacted. ✓
- no reactants have reacted.
- the products have decomposed.
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Worksheet
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Presentation
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Video
Lesson Details
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.
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.
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.
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