✅ 7. Required Practical: How Rates Of Reaction Are Affected By Concentrations Of Acids (C8)

Question 1

What is the Aim of this Practical

Answer 1

Magnesium reacts with hydrochloric acid: Mg (s) + 2HCl (aq) —> MgCl2 (aq) + H2 (g)

The aim of this practical is to see how changing the concentration of the acid affects the rate of the reaction. You will measure the volume of hydrogen gas formed in the first 20 seconds and use this to find the mean rate of the reaction in the first 20 seconds in cm^3/s.

Question 2

My Hypothesis for the Practical

Answer 2

I think that increasing the concentration of hydrochloric acid will increase the rate of reaction, as this means there will be a larger number of hydrochloric acid particles. More particles will result in more possible collisions with the magnesium particles, and therefore more collisions lead to more successful collisions, which may lead to a quicker rate of reaction as a result.

Question 3

Health and Safety Precautions for this Practical

Answer 3

• Hydrochloric acid is an irritant

- Hydrogen and magnesium are flammable. There should be no naked flames in the labatory

Question 4

Equipment Needes for this Practical

Answer 4

• Clamp Stand
• Clamp
• Pipette
• Conical Flask (with tube and bung)
• Measuring Cylinders
• Water
• Gas Syringe
• A Few (5 or more) Magnesium Ribbons
• 2.0 Mol Hydorchloric Acid
• Timer

Question 5

Method for this Practical

Answer 5

1. Prepare 20cm^3 of 0.4 mol/dm^3 hydrochloric acid by mixing 4cm^3 Of 2.0mol dm^3 hydrochloric acid with 16cm^3 of water in a bliling tube using measuring cyclinders. Place the boiling tube in a rack
2. Set up a gas syringe using a clamp stand (ensuring that the syringe is fixed on appropriately)
3. Cut a 3cm length of magnesium ribbon amd rub it down with emery cloth/sandpaper.
4. Add the magnesium ribbon to the hydrochloric acid, attaching the delivery tube straight away and starting the timer for 20 seconds.
5. Record the volume of gas formed in 20 seconds
6. Repeat the experiment with the concentrations of acid (by adding different amounts of HCl and water), using a new piece of magnesium ribbon every time.
7. Record the results in the results table, making sure to subtract the dead volume from the bung being inserted into the flask)

Question 6

What is the Independant Variable

Answer 6

In this experiment, it seems as the Independant Variable is the Concentration of the Acid (mol/dm^3) because it is the variable that his altered throughout the experiment to see the effect it has on the time.

Question 7

What is the Dependant Variable

Answer 7

The Dependant Variable is the the volume of hydrogen produced (cm^3) to calculate the rate of reaction (cm^3/s) . This is because the dependant variable is the variable that is being tested and measured for.

Question 8

What are the Control Variables

Answer 8

The Control Variables are the volume of the acid that is reacted with the magnesium ribbon, the catalyst used, and the temperature the reaction was performed in. These are control variables because these are kept the same throughout the experiment to ensure that it is kept as a fair test.

Question 9

How Should The Results Table be laid out?

Answer 9

The ‘Temperature of Na2S2O3 (°C) is on the left

The ‘Time Taken for cross to disappear (s) is in the middle

The rate of reaction (s^-1) is on the right

Question 10

What should the Graph look like

Answer 10

The ‘Temperature of Na2S2O3 (°C) is on the X-Axis

The ‘Time Taken for cross to disappear (s) is on the Y-Axis

The graph starts out goin across, and then curve upwards.

Question 11

Explain Why The Control Variables Had To Be Controlled In This Experiment?

Answer 11

The control variables had to be controlled because they would’ve affected the rate of reaction each time, resulting in what would be an unfair test.

Question 12

Describe What The Results Tell Us How Changing The Concentration Affects The Rate Of Reaction?

Answer 12

Overall, the results tell us that increasing the concentration of acid increases the rate of reaction. This means that as the concentration is doubled, the rate of reaction should also have doubled, creating what would be a linear graph.

Question 13

Explain Why Concentration Has This Effect On The Rate Of Reaction Using The ‘Collision Theory’

Answer 13

The concentration will have an effect on the rate, as a higher concentration of acid means that there are a larger number of acid particles in the same volume. More acid particles means there are more possible collisions with magnesium particles. More collisions lead to more successful collisions which will lead to a quicker rate of reaction.

Question 14

The Rate Of Reaction Should Be Proportional To The Concentration Of The Acid? Do My Results Show This And Justify My Answer.

Answer 14

My results don’t justify the fact that the rate of reaction should be proportional to the concentration of the acid, as my results are incorrect. In reality, the rate of reaction is proportional to the concentration of the acid, as the rate of reaction doubles as the concentration doubles, meaning there would be a linear line of best fit on a graph.

Question 15

A Student Found That When Water Rather Than Acid Was Used In The Experiment, The Syringe Did Show A Few cm^3 of Gas In The Syringe. This Is Called A Zero-Point Error. Explain Why This Occurs And Explain What Type Of Error This Is?

Answer 15

A zero-point error is when the syringe shows a few cm^3 of gas. It is because of the fact that some air is already inside of the concial flask is pushed into the syringe when the bung is put into the top. As a result, this is a systematic error as this will happen every time you place the bung into the flask.

Question 16

A Mean Rate Of Reaction Was Calculated In Each Experiment. Explain Why This Is Called A Mean Rate?

Answer 16

It is called a mean rate because it is not an exact rate of a reaction at a certain point, it’s instead the mean rate of reaction, over a period of time, such as 20 seconds, which is why it’s a mean rate of reaction.

Question 17

Identify Two Significant Problems With This Experiment And Suggest Ways In Which These Could Be Reduced?

Answer 17

Problem 1: The magnesium was floating on the surface of the acid instead of being fully submerged

Solution: The solution could be to give the reaction mixture a slight swirl in order to ensure that the magneisum ribbon is fully submerged at the start of the reaction.

Problem 2: More acid produces more heat as it’s an exothermic reaction, and heat affects the rate of reaction.

Solution: The solution to this could be to make sure that each reaction always takes place at the same temperature (to make sure that the atmosphere the reaction takes place in is the same temperature), as this would otherwise have an affect on the efficiency of the reaction. The temperature can be measured through a thermometer.