Volume of acid (25cm3)
Mass of Magnesium (0.1g)
I will make sure the gas syringe is connected correctly and securely to the side arm conical, so no hydrogen gas can escape.
I will start the syringe at 0 for each run.
Also I would make sure to put the bung on quickly, to prevent the hydrogen gas escaping.
Preliminary Work
I am doing preliminary work to show that when magnesium reacts with hydrochloric acid it produces hydrogen gas. It will also be useful for judging the amount of hydrochloric acid and magnesium required. For example, if the reaction takes too long I can decrease my mass of magnesium or the volume of hydrochloric acid but if it is too short I can increase the amount of magnesium or the volume of hydrochloric acid.
To see if the reaction between magnesium and hydrochloric acid produces hydrogen I will mix these elements and then test the resultant reaction with a lighted splint to see if it produces a squeaky pop.
The apparatus I will use for my preliminary work is: -
- Magnesium turnings
- Hydrochloric acid (1M)
- Test Tube
- Bunsen Burner
- Spatula
- Splint
- Test tube rack (optional)
To keep the experiment safe I will do the following: -
- Wear safety glasses
- Tuck tie in
- Mop up any spillages.
Method for preliminary work.
- Place 3cm3 of hydrochloric acid in a test tube
- Then, add half a spatula full of magnesium turnings to the hydrochloric acid in the test tube.
- Place thumb on top of test tube, so no gas can escape
- Wait a few seconds for the reaction to progress
- Then, light a splint from a Bunsen burner flame and place it over the test tube.
- Note what happens.
Results
The results for the experiment were that when the magnesium reacts with the hydrochloric acid it does produce hydrogen gas we know this because the hydrogen made a popping sound when it came into contact with the flame on the splint.
To see how much magnesium and hydrochloric acid I need in my actual experiment I have devised the following mole equation.
Mg + 2HCL MgCl2 + H2
1 mole + 2 moles 1 mole + 1 mole
For magnesium
24g 24000cm3
24000/240 = 100
24/240= 0.1g
For HCL
Moles = mass/RMM = 0.1g / 24 = 0.00416 x 2 = 0.0083
1 molar concentration
Volume = moles / molarity = 0.0083 dm3 = 8.3cm3
This calculation shows that we should use 0.1g of magnesium and that we should use a minimum of 8.3 cm 3 of Hydrochloric acid.
Apparatus
Magnesium turnings (0.1g)
Hydrochloric acid (25cm 3)
Glass syringe
Clamp stand
Stop clock
Scales
Spatula
Side arm conical
Beaker
Measuring cylinder
Thermometer
Bunsen Burner
Safety
- Wear safety glasses
- Tuck tie in
- Mop up any spillages
- Don’t light hydrogen gas
Also for safety I will consult secondary sources, I will use hazard cards to do this.
Magnesium
This metal is hard to ignite but burns vigorously and is difficult to extinguish. Powdered magnesium is particularly dangerous, if blown into a Bunsen flame. Extinguish fires by smothering with sand.
If swallowed: - Wash mouth and give a glass or two of water, keep victim under surveillance, as diarrhea is possible. Medical attention should be obtained if discomfort persists.
If gets in eye’s:- Flood eye with gently running water for 10 minutes.
If spilt:- Scoop up as much as possible, wash spillage.
Hydrochloric acid.
Hydrochloric acid is corrosive so be wary you don’t burn your self.
If swallowed:- Give plenty of water. Get medical attention.
If inhaled:- Move victim to fresh are to rest.
If spilt:- Wear eye protection and gloves.
Hydrogen
Hydrogen is extremely flammable so don’t be tempted to light the gas.
Do not attempt to breath hydrogen to change pitch of voice.
Diagram
Method
- Measure out 25cm3 of hydrochloric acid using a measuring cylinder and place it in a beaker.
- Measure out 0.1g of Magnesium using some scales and place it in the side arm conical.
- Hold the glass syringes with a clamp and stand to the height of 5 cm
- Place the rubber of the side arm conical over the end of the glass syringe.
- Place the hydrochloric acid in with the magnesium turnings in the side arm conical and quickly place the bung on top.
- Take readings of how much hydrogen is being produced every 5 seconds from the glass syringes use a stop clock to do this.
-
Repeat the experiment 5 times with different temperatures every time. I will use the following temperatures: 20 0C, 30 0C, 40 0C, 50 0C, and 60 0C.
- To heat the acid at these temperatures I will use a Bunsen burner and check the readings with a thermometer.
- Repeat each run 3 times and take an average of the over all volumes.
Results:- do them ya self
Rate of Chemical Reaction between Magnesium and Hydrochloric Acid
Objectives
The objective of the experiment is to demonstrate that the rate of the reaction increases with rise in temperature of hydrochloric acid.
This is due to the molecules in the hydrochloric acid gaining energy from the heat. Consequently, the molecules have increased kinetic energy, which will produce more activation energy. The particles will have more successful collisions resulting in a faster reaction rate.
Experimental Results
The results of the experiment have been tabulated, with the data also plotted on graphs showing the volume of hydrogen gas produced against time of reaction, for various temperature of HCL acid from 20° to 60°. The tables and charts are included with this text.
Evaluation
The results of the experiment were overall quite successful.
The first chart (1) shows that at each acid temperature the reaction rate, or the volume of gas produced, increases steadily over the first 60s and then gradually levels off to a stop at between 100s – 150s. The reaction is quickest at the start as there is more magnesium to react with the acid. This effect is what I predicted.
I have also plotted separate charts for each acid temperature (20°- 60°). On these charts I have calculated the gradient at various points on the curve to illustrate the change in reaction rate. In each case I have taken the gradient over a period of 30 seconds, when the curve was smooth (with no irregular readings). The gradient is established by dividing the change in volume by the change in time, which was always 30 seconds.
Examining the curves for each acid temperature shows that the gradient of the curves are steeper at the start of the reaction and then gradually fall off with time. For example, the table below shows the change in gradient, for increasing time for acid at 30° C.
Table 1: Curve gradients with increasing time, for acid at 30 degrees C.
The other curves for also demonstrate this same pattern.
The curves also show that that the gradients are steeper as the acid temperature is increased. For example, if you look at the gradient at 20 seconds for each acid temperature, the gradients increase with increasing acid temperature.
The curves therefore additionally demonstrate that the reaction rate increase with the temperature of the acid. This confirms my prediction which was based on the theory that by increasing the temperature of the acid the activation energy of the particles gets higher, so the particles in the hydrochloric acid will collide more with the magnesium thereby increasing the reaction rate at the start.
The gradients shown on Chart 2, also show that the gradient of the reaction curve decreases with time, demonstrating that the reaction rate slows down with time. Again this is in line with my predictions.
For my last chart I have plotted the reaction rate at the end of the each reaction (the time the reaction finished divided by 1), for each acid temperature from 20° to 60°. This chart confirms that the reaction rate increase with acid temperature, as per my predictions.
Experimental Errors
In my experiment the correct amount of hydrogen wasn’t produced. This is due to the hydrogen escaping before the bung is placed on top. The hydrogen could also have escaped from the connections between the side arm conical and the gas syringe, so again this could have affected my results.
If I were to repeat the experiment again I would use: -
- A dropping funnel to add the hydrochloric acid to the magnesium, this would allow me to add the hydrochloric to the magnesium turnings without placing the bung on. So this would allow me to put the hydrochloric acid in with the magnesium, without any hydrogen getting released before I had chance to start the stop clock.
- A water bath to heat the acid instead of a Bunsen burner, because if I was using a water bath I could be more accurate then if I was using a Bunsen burner.
- A pipette to measure the volume of the acid instead of using a measuring cylinder. I would do this because I could achieve a much more accurate reading when using a pipette.
- More accurate scales to weigh out the magnesium turnings.
- Be more accurate whilst reading the stop clock.
- Different types of acid, instead of hydrochloric I could use phosphoric acid.
- Different temperatures.
Despite some potential experimental error, the evidence taken from the experiment is reliable, as each of the curves demonstrated the same trend of increasing reaction rate with temperature. This is also confirmed by the rate of reaction chart (7), which shows an increasing reaction rate with time for each temperature.
All these effects were predicted in the theoretical review of the experiment presented at the plan section of the report.
