Preliminary experiments and results:
For my main investigation and experiment after analysing the preliminary results. At 0.5M the decomposition of the magnesium was very slow and therefore for my main investigation I will use 1M, 1.2M, 1.4M, 1.6M, 1.8M and 2M concentrations, to see the effect this has on the rate of reaction.
Apparatus:
- 100ml-measuring cylinder: Filled with water and when gas enters out of delivery tube water will escape through bottom and at the end of the reaction I will be left with an air pocket at the top of the cylinder in which I will read off and find out the volume of gas produced.
- 2x 10ml measuring cylinders: To measure out HCL and water.
- Stop-clock: To measure the time intervals accurately and total time taken for experiment.
- Delivery tube: One end is connected to conical flask and other to bottom of 100ml measuring cylinder. This will transport the hydrogen gas produced by the reaction.
- Glass trough: Filled with water and 100ml-measuring cylinder placed in this. End of delivery tube to be put under 100ml-measuring cylinder, so when gas is produced water can escape and readings can be taken.
- Distilled water: pure water.
- Goggles: protect eyes from HCL, in the case of it being splashed in eyes.
- Conical flask: To put dilute hydrochloric acid and magnesium strip. Used for when the reaction happens.
- HCl and magnesium ribbon: the two that will react together to give me results.
Diagram: (drawn on final copy)
Method:
- Collect all apparatus
- Get 100ml-measuring cylinder and fill fully with water and also fill the trough ¾ full.
- Cover 100ml-measuring cylinder with hand and tip upside down into trough without letting water escape.
- Add 1m concentration of dilute hydrochloric acid to conical flask. (Add 10ml³ of 2m HCl and 10ml³ distilled water).
- Get the end of delivery tube and put into trough and under 100ml-measuring cylinder.
- Get 2cm magnesium ribbon and add to dilute hydrochloric acid, start stop clock immediately and at the same time cover conical flask with rubber side of delivery tube.
- Every 10 seconds record volume of hydrogen produced.
- When magnesium strip has dissolved completely stop the stop clock and record total time and total volume of hydrogen produced.
- Repeat for 1.2m, 1.4m, 1.6m 1.8m and 2.0m
Safety:
I will wear goggles to protect eyes from HCl, in the case of it being splashed in eyes. I will wear non-porous gloves when handling HCl, to avoid contact with skin.
Prediction and justification:
I predict that as the concentration of hydrochloric acid increases, the time taken for the magnesium ribbon to completely dissolve will be reduced. I also predict that as the concentration doubles the rate of reaction will double, this is because there are more molecules in a given volume, in 2m hydrochloric acid there are twice as much molecules than in 1m of hydrochloric acid.
The word equation for the reaction is:
Magnesium(s) + Hydrochloric acid(l)￫Magnesium chloride(l) + Hydrogen(g)
The Symbol equation for the reaction is:
Mg(s) + 2HCL (l) ￫ MgCl2 (l) + H2 (g)
In order for the magnesium and acid particles to react together they must collide with each other and this collision must have enough energy, so the two can react.
If there are lots of reactions within a given minute, then there is a high reaction rate and a lot of the product is produced. If the reaction is slow, the reaction rate is low. The rate of reaction depends on how many successful collisions there are in a given unit of time.
If the concentration of the acid is high, the rate of reaction will be faster than if the concentration is low this is because there are more particles in a given volume in a higher concentrated solution. In my investigation I will be using between 1M and 2M, in the higher concentration acid there are more particles per ml, therefore more reactant particles and more chance of a reaction-taking place. In more dilute acid, there are not as many acid particles, which means there is less chance of the acid particles colliding and reacting with magnesium.
The reaction between HCl and magnesium ribbon is exothermic. Which means heat is given out. During a chemical reaction, old bonds are broken and new bonds are formed. Energy is released when new bonds are formed, so bond formation is an exothermic process. In this exothermic reaction new bonds are formed to make magnesium chloride and hydrogen. The energy released in bond formation is greater than the energy used in breaking old bonds.
Bond forming
Exothermic
Observations
I have recorded my results accurately because I have followed my fair test accurately for each experiment. I have chosen the correct headings for my table because I have put morality at the top and time along the side and displayed all the results using correct headings and so that it can be seen clearly. I have written down the units for each factor such as, time: secs and M for molarity.
Analysing evidence
The main link in the graph is that as concentration of hydrochloric acid increases, so does rate of reaction. This is because as the concentration increases there are more reactant particles in the hydrochloric acid per cm³, this leads to more collisions per second and thus increasing the rate of reaction at which the magnesium is decomposed.
In my prediction I wrote, “I predict that as the concentration of hydrochloric acid increases, the time taken for the magnesium ribbon to completely dissolve will be reduced.” This part of my prediction was correct. This was because as the concentration of the hydrochloric acid was increased the time taken for the magnesium strip to decompose and disappear was shorter. My prediction went on to say “I also predict that as the concentration doubles the rate of reaction will double, this is because there are more molecules in a given volume, in 2m hydrochloric acid there are twice as much molecules than in 1m of hydrochloric acid”, the rate of reaction did not double according to my results. This was because at 1 molar the rate of reaction was 1, and at 2 molar the rate of reaction was more than quadrupled to 4.2.
I conclude that if you double the concentration of the acid, the rate of reaction will quadruple, this is because the reactant particles are closer together in a concentrated solution. The closer together they are, the more often they will collide, which makes it a higher chance of a reaction between the hydrochloric acid and magnesium. Because there are more particles in the solution there is a greater chance that they would collide and react. The reaction needed activation energy to begin the reaction, in this reaction the hydrochloric acid gave the energy for the reaction to begin, this was because the hydrochloric acid bombarded the magnesium particles to make magnesium chloride and hydrogen.
Evaluation
I think enough data was collected to reach a conclusion of as the concentration of a solution is increased the rate of reaction is also increased. This is because the reactant particles are closer together in a concentrated solution. The closer together they are, the more often they will collide, which makes it a higher chance of a reaction between the hydrochloric acid and magnesium.
My investigation could be improved if I used a gas syringe to record the volume of gas produced by the reaction. My current method was to, get 100ml-measuring cylinder and fill fully with water and also fill the trough ¾ full. Cover 100ml-measuring cylinder with hand and tip upside down into trough without letting water escape. Add 1m concentration of dilute hydrochloric acid to conical flask. (Add 10ml³ of 2m HCl and 10ml³ distilled water). Get the end of delivery tube and put into trough and under 100ml-measuring cylinder. Get 2cm magnesium ribbon and add to dilute hydrochloric acid, start stop clock immediately and at the same time cover conical flask with rubber side of delivery tube. I realised that there was always a small air bubble at the top of the 100ml measuring cylinder, which could not filled with water, this may have given inaccurate readings of the amount of gas produced. Also there was a delay of up to 1 second between when the magnesium ribbon was dropped into the flask and the delivery tube being put into the flask, which meant that the first second or two of gas produced was not being transported into the 100ml measuring cylinder, which gave partly inaccurate results. If I used a gas syringe, it would have been easier and quicker to put he rubber end onto the conical flask.
Further work that can be done is measuring higher concentrations to see if between 2M and 4M the rate of reaction doubles and test with different acids to see what effect the concentration has on the rate of reaction for the acids.
