What is the purpose of the Core Practical: Investigating Rate of Reaction?

To investigate how changing a variable (surface area or concentration) affects the rate of a chemical reaction, using either gas volume collection or the disappearing cross method.

In a gas volume experiment to investigate rate of reaction, what reaction is commonly used and what gas is produced?

Marble chips (CaCO 3 ) react with hydrochloric acid (HCl). Carbon dioxide (CO 2 ) is produced and collected using a gas syringe.

When investigating how surface area affects rate of reaction using marble chips and HCl, the independent variable is the _____ of the marble chips, the dependent variable is the _____ of CO 2 collected, and the controlled variables include the volume and concentration of _____ .

When investigating how surface area affects rate of reaction using marble chips and HCl, the independent variable is the size (surface area) of the marble chips, the dependent variable is the volume of CO 2 collected, and the controlled variables include the volume and concentration of hydrochloric acid .

Describe the method for the disappearing cross experiment to investigate how concentration affects rate of reaction.

Measure 50 cm³ of sodium thiosulfate solution into a conical flask placed over a paper cross. Measure 5 cm³ of dilute HCl. Add the acid and immediately start the stopwatch. Look down through the solution and stop the stopwatch when the cross can no longer be seen. Repeat with different concentrations of sodium thiosulfate.

How is rate of reaction calculated from experimental data?

Rate of reaction = quantity of product formed ÷ time taken Units depend on what is measured: g/s (mass loss) or cm³/s (gas volume).

How do you find the rate of reaction at a specific point on a curved concentration-time or volume-time graph?

Draw a tangent to the curve at that point. Calculate the gradient of the tangent: Rate = Δ(product) ÷ Δ(time) Extend the tangent as far as possible to reduce uncertainty.

State three safety precautions when investigating rate of reaction using hydrochloric acid and sodium thiosulfate.

Wear safety goggles — HCl can irritate eyes and skin.\n2. Avoid inhaling SO 2 produced in the disappearing cross experiment — use a fume cupboard; asthmatics need extra care.\n3. Keep magnesium away from naked flames as it is flammable.

When using marble chips and HCl to investigate rate of reaction, why does using smaller chips increase the rate?

Smaller chips have a greater surface area. More CaCO 3 particles are exposed to HCl, so collisions between reactant particles are more frequent and successful, increasing the rate of reaction.

In the disappearing cross experiment, sodium thiosulfate reacts with HCl to produce a yellow precipitate of _____ , which makes the cross disappear. A higher concentration of sodium thiosulfate means the cross disappears _____ .

In the disappearing cross experiment, sodium thiosulfate reacts with HCl to produce a yellow precipitate of sulfur , which makes the cross disappear. A higher concentration of sodium thiosulfate means the cross disappears faster .

Why is cotton wool placed in the mouth of the flask when measuring mass loss on a balance?

Cotton wool allows CO 2 gas to escape (so mass loss can be recorded) but prevents any liquid droplets or solid particles from being ejected from the flask during a vigorous reaction.

Define the term collision theory .

A theory that explains how rates of reaction depend on the frequency and energy of collisions between reactant particles.

True or False? All collisions result in a chemical reaction.

False. Not all collisions result in a chemical reaction. Unsuccessful collisions happen when the colliding species do not have enough energy to break the necessary bonds.

True or False? Increasing concentration increases the number of collisions per second.

True. Increasing the concentration of a solution will increase the number of reactant particles in a given volume, allowing more frequent and successful collisions per second.

How does increasing temperature increase the rate of reaction?

Increasing temperature increases the kinetic energy of the particles, leading to more frequent and successful collisions with energy greater than the activation energy.

How does increasing surface area affect the rate of reaction?

Increasing the surface area of a solid reactant increases the rate of reaction because more surface area is exposed to the other reactant, producing a higher number of collisions per second.

True or False? For every 10 degree increase in temperature, the rate of reaction approximately doubles.

True. As a rule of thumb for every 10 degree increase in temperature, the rate of reaction approximately doubles.

State the relationship between the number of collisions and the number of particles.

The number of collisions is proportional to the number of particles present.

Define the term successful collision .

A successful collision is a collision between reactant particles that leads to the formation of product molecules.

True or False? The rate of reaction can be calculated from the gradient of a concentration-time graph.

True. The steeper the gradient, the faster the rate of reaction.

True or False? The steeper the gradient of the line in a rates graph then the slower the rate of reaction.

False. The steeper the gradient of the line in a rates graph then the faster the rate of reaction.

Define the term catalyst .

A catalyst is a substance that increases the rate of a reaction without being used up itself. It is regenerated at the end of the reaction.

How does a catalyst work?

A catalyst speeds up the rate of a reaction by providing an alternative pathway with lower activation energy.

True or False? Catalysts are used up in a reaction.

False. Catalysts are not used up in the reaction.

True or False? Catalysts are written as part of the chemical equation.

False. Although catalysts are not part of the overall reaction, they may be written over the arrow in reaction equations, indicating the conditions.

True or False? Only small amounts of a catalyst are needed in a reaction.

True. Only small amounts of a catalyst are needed in a reaction as the catalyst is not used up.

How can you show that a chemical is a catalyst?

You can show that a substance is a catalyst by: Weigh the catalyst before the reaction Weigh the catalyst after the reaction The mass should remain the same

True or False? Enzymes are biological catalysts.

True. Enzymes are nature's catalysts, biological substances that catalyse reactions in living cells.

Define the term enzyme .

An enzyme is a biological catalyst made from protein that speeds up chemical reactions in cells.

What types of reactions do enzymes catalyse?

Enzymes catalyse important biological reactions such as respiration, photosynthesis, and protein synthesis.

True or False? Enzymes can work on any type of molecule when presented with a mixture of reactants.

False. Enzymes are very selective and will only work on very specific molecules when presented with a mixture of reactants.

What biological catalyst is used in fermentation?

Yeast enzymes catalyse the fermentation of sugars to produce ethanol and carbon dioxide.

True or False? Enzymes can work at low temperatures.

True. Enzymes can work at low temperatures.

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Rates of Reaction (Edexcel GCSE Combined Science: Chemistry): Flashcards

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What is the purpose of the Core Practical: Investigating Rate of Reaction?
To investigate how changing a variable (surface area or concentration) affects the rate of a chemical reaction, using either gas volume collection or the disappearing cross method.
In a gas volume experiment to investigate rate of reaction, what reaction is commonly used and what gas is produced?
Marble chips (CaCO₃) react with hydrochloric acid (HCl). Carbon dioxide (CO₂) is produced and collected using a gas syringe.
When investigating how surface area affects rate of reaction using marble chips and HCl, the independent variable is the _____ of the marble chips, the dependent variable is the _____ of CO₂ collected, and the controlled variables include the volume and concentration of _____.
When investigating how surface area affects rate of reaction using marble chips and HCl, the independent variable is the size (surface area) of the marble chips, the dependent variable is the volume of CO₂ collected, and the controlled variables include the volume and concentration of hydrochloric acid.
Describe the method for the disappearing cross experiment to investigate how concentration affects rate of reaction.
1. Measure 50 cm³ of sodium thiosulfate solution into a conical flask placed over a paper cross.
2. Measure 5 cm³ of dilute HCl.
3. Add the acid and immediately start the stopwatch.
4. Look down through the solution and stop the stopwatch when the cross can no longer be seen.
5. Repeat with different concentrations of sodium thiosulfate.
How is rate of reaction calculated from experimental data?
Rate of reaction = quantity of product formed ÷ time taken
Units depend on what is measured: g/s (mass loss) or cm³/s (gas volume).
How do you find the rate of reaction at a specific point on a curved concentration-time or volume-time graph?
Draw a tangent to the curve at that point. Calculate the gradient of the tangent:
Rate = Δ(product) ÷ Δ(time)
Extend the tangent as far as possible to reduce uncertainty.
State three safety precautions when investigating rate of reaction using hydrochloric acid and sodium thiosulfate.
1. Wear safety goggles — HCl can irritate eyes and skin.\n2. Avoid inhaling SO₂ produced in the disappearing cross experiment — use a fume cupboard; asthmatics need extra care.\n3. Keep magnesium away from naked flames as it is flammable.
When using marble chips and HCl to investigate rate of reaction, why does using smaller chips increase the rate?
Smaller chips have a greater surface area. More CaCO₃ particles are exposed to HCl, so collisions between reactant particles are more frequent and successful, increasing the rate of reaction.
In the disappearing cross experiment, sodium thiosulfate reacts with HCl to produce a yellow precipitate of _____, which makes the cross disappear. A higher concentration of sodium thiosulfate means the cross disappears _____.
In the disappearing cross experiment, sodium thiosulfate reacts with HCl to produce a yellow precipitate of sulfur, which makes the cross disappear. A higher concentration of sodium thiosulfate means the cross disappears faster.
Why is cotton wool placed in the mouth of the flask when measuring mass loss on a balance?
Cotton wool allows CO₂ gas to escape (so mass loss can be recorded) but prevents any liquid droplets or solid particles from being ejected from the flask during a vigorous reaction.
Define the term collision theory.
A theory that explains how rates of reaction depend on the frequency and energy of collisions between reactant particles.
True or False?
All collisions result in a chemical reaction.
False.
Not all collisions result in a chemical reaction. Unsuccessful collisions happen when the colliding species do not have enough energy to break the necessary bonds.
True or False?
Increasing concentration increases the number of collisions per second.
True.
Increasing the concentration of a solution will increase the number of reactant particles in a given volume, allowing more frequent and successful collisions per second.
How does increasing temperature increase the rate of reaction?
Increasing temperature increases the kinetic energy of the particles, leading to more frequent and successful collisions with energy greater than the activation energy.
How does increasing surface area affect the rate of reaction?
Increasing the surface area of a solid reactant increases the rate of reaction because more surface area is exposed to the other reactant, producing a higher number of collisions per second.
True or False?
For every 10 degree increase in temperature, the rate of reaction approximately doubles.
True.
As a rule of thumb for every 10 degree increase in temperature, the rate of reaction approximately doubles.
State the relationship between the number of collisions and the number of particles.
The number of collisions is proportional to the number of particles present.
Define the term successful collision.
A successful collision is a collision between reactant particles that leads to the formation of product molecules.
Which line shows magnesium powder reacting with acid and which line shows magnesium ribbon reacting with acid?
Line A shows magnesium powder reacting with acid and line B shows magnesium ribbon reacting with acid.
How long does the reaction take to complete?
The reactions takes 30 seconds to complete. The point at which the line plateaus is when the reaction is complete.
Which line shows magnesium ribbon reacting with concentrated acid and which line shows magnesium ribbon reacting with dilute acid?
Line A is magnesium reacting with concentrated acid, and line B is magnesium reacting with dilute acid.
At which point is the reaction the fastest?
The reaction is the fastest at the beginning of a reaction. Between 0 and 10 seconds.
True or False?
The rate of reaction can be calculated from the gradient of a concentration-time graph.
True.
The steeper the gradient, the faster the rate of reaction.
True or False?
The steeper the gradient of the line in a rates graph then the slower the rate of reaction.
False.
The steeper the gradient of the line in a rates graph then the faster the rate of reaction.
State the equation in terms of gradient.
The equation to calculate the gradient is:
Gradient = $\frac{∆ y}{∆ x}$
Define the term catalyst.
A catalyst is a substance that increases the rate of a reaction without being used up itself. It is regenerated at the end of the reaction.
How does a catalyst work?
A catalyst speeds up the rate of a reaction by providing an alternative pathway with lower activation energy.
True or False?
Catalysts are used up in a reaction.
False.
Catalysts are not used up in the reaction.
True or False?
Catalysts are written as part of the chemical equation.
False.
Although catalysts are not part of the overall reaction, they may be written over the arrow in reaction equations, indicating the conditions.
True or False?
Only small amounts of a catalyst are needed in a reaction.
True.
Only small amounts of a catalyst are needed in a reaction as the catalyst is not used up.
How can you show that a chemical is a catalyst?
You can show that a substance is a catalyst by:
- Weigh the catalyst before the reaction
- Weigh the catalyst after the reaction
- The mass should remain the same
Which letter represents the activation energy for a reaction using a catalyst?
The letter which represents the activation energy for a reaction using a catalyst is C.
True or False?
Enzymes are biological catalysts.
True.
Enzymes are nature's catalysts, biological substances that catalyse reactions in living cells.
Define the term enzyme.
An enzyme is a biological catalyst made from protein that speeds up chemical reactions in cells.
What types of reactions do enzymes catalyse?
Enzymes catalyse important biological reactions such as respiration, photosynthesis, and protein synthesis.
True or False?
Enzymes can work on any type of molecule when presented with a mixture of reactants.
False.
Enzymes are very selective and will only work on very specific molecules when presented with a mixture of reactants.
What biological catalyst is used in fermentation?
Yeast enzymes catalyse the fermentation of sugars to produce ethanol and carbon dioxide.
True or False?
Enzymes can work at low temperatures.
True.
Enzymes can work at low temperatures.
Which enzyme, A or B, will fit substrate X?
Enzyme A will fit substrate X.

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