Rate of reaction of magnesium with hydrochloric acid
Magnesium reacts with dilute hydrochloric acid in a conical flask which is connected to an inverted measuring cylinder in a trough of water. The volume of hydrogen gas produced is measured over a few minutes, and the results are used to plot a graph.
Read our standard health & safety guidance
Lesson organisation
This is intended as a class practical. It is best if the students work in pairs because setting up and starting the experiment requires more than one pair of hands. One student can add the magnesium ribbon to the acid and stopper the flask, while the other starts the stopclock. During the experiment, one student can take the readings while the other records them. The experiment itself takes only a few minutes. But allow at least 30 minutes to give students time to set up, take readings and draw graph.
Hydrogen gas (Extremely flammable) is generated in the experiment. Students should not have access to any source of ignition.
Apparatus and Chemicals
Eye protection
Each group of students will need:
Conical flask (100 cm3)
Single-holed rubber bung and delivery tube to fit conical flask (see note 3)
Trough (or plastic washing-up bowl)
Measuring cylinders (100 cm3), 2
Clamp stand, boss and clamp
Stopclock
Graph paper
Each group of students will need access to:
Magnesium ribbon (Low hazard) cut into 3 cm lengths (see note 1)
Dilute hydrochloric acid, 1 mol dm-3 (Low hazard at this concentration) (see note 2)
Below is a diagram of the set-up
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Technical notes
Magnesium ribbon (Low hazard) Refer to CLEAPSS Hazcard 59A
Hydrochloric acid (Low hazard at concentration used) Refer to CLEAPSS Hazcard 47A and CLEAPSS Recipe Card 31
Hydrogen gas (Extremely flammable) Refer to CLEAPPS Hazcard 48
1 The magnesium ribbon should be clean and free from obvious corrosion or oxidation. Clean if necessary by rubbing lengths of the ribbon with fine sandpaper to remove the layer of oxidation.
2 The hydrochloric acid should be about 1 mol dm-3 for a reasonable rate of reaction. Each experiment run will need 50 cm3. Though low hazard, eye protection is necessary as you may get a spray as tiny bubbles burst.
3 The bungs in the flasks need to be rubber. Corks are too porous and will leak. The tube through the bung should be a short section of glass, and then a flexible rubber tube can be connected.
4 Gas syringes can be used instead of troughs of water and measuring cylinders. But these are very expensive and are probably best used by the teacher in a demonstration. Syringes should not be allowed to become wet, or the plungers will stick inside the barrels.
5 Ensure that all naked flames are extinguished, and that there are no other sources of ignition available to students.
Procedure
SAFETY: Wear eye protection throughout. Ensure that there are no naked flames.
a Measure 50 cm3 of 1 mol dm-3 hydrochloric acid using one of the measuring cylinders. Pour the acid into the 100 cm3 conical flask.
b Set up the apparatus as shown in the diagram. Half fill the trough or bowl with water.
c Fill the other measuring cylinder with water, and make sure that it stays filled with water when you turn it upside down.
d When you are ready, add a 3 cm strip of magnesium ribbon to the flask, put the bung back into the flask as quickly as you can, and start the stopclock.
e Record the volume of hydrogen gas given off at suitable intervals (eg 10 seconds). Continue timing until no more gas appears to be given off.
Teaching notes
The equation for the reaction is:
magnesium + hydrochloric acid → magnesium chloride + hydrogen
Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
Students follow the rate of reaction between magnesium and the acid, by measuring the amount of gas produced at 10 second intervals.
3 cm of magnesium ribbon typically has a mass of 0.04 g and yields 40 cm3 of hydrogen when reacted with excess acid. 50 cm3 of 1 mol dm-3 hydrochloric acid is a six-fold excess of acid.
In this reaction, the magnesium and acid are gradually used up. However the acid is in excess, so it is mainly the loss of magnesium (surface area becomes smaller) that causes the change in the rate.
If a graph of volume (y-axis) against time (x-axis) is drawn, the slope of the graph is steepest at the beginning. This shows that the reaction is fastest at the start. As the magnesium is used up, the rate falls. This can be seen on the graph, as the slope becomes less steep and then levels out when the reaction has stopped (when no more gas is produced).
The reaction is exothermic, but the dilute acid is in excess and the rise in temperature is only of the order of 3.5˚C. There is some acceleration of the reaction rate due to the rise in temperature. Some students might notice the flask becoming slightly warm and they could be asked how this would affect the rate of reaction, and how they might adapt the experiment to make it a ‘fair test’.
Health & Safety checked, June 2007
Updated 4 Mar 2008Average rating: 
3 out of 5
Your reviews
0.04g of Mg is 0.00167 mol, which when fully reacted gives 0.00167 mol of H2 which is only 4 ml. Editor: actually not - 0.00167 mol H2 will have a volume of 0.00167 x 24000 ml = 40 ml at room temprature and pressure.
Submitted by: ol on 18 December 2008
Good experiment for practical data analysis GCSE coursework, however tricky for students to acheive accurate data.
Submitted by: Caroline on 26 June 2008
Excellent. All I needed was in this peice of work ....fantastic
Submitted by: neel on 26 June 2008
I almost lost hope on my project...until i placed my eyes on this site...
Submitted by: Azmi on 4 August 2008
I did this experiment in class. I have all the data, but I need somebody to explain to me how I calculate the concentration (M), because my rate of reaction just increases. It should in the first part, not in the last. HELP PLEASE!!
Submitted by: Maricarmen on 18 December 2008
rubbish does not help
Submitted by: john on 17 November 2008
Good experiment, but I recommend 2 mol dm-3 HCl. Also a point, it is quite hard to get accurate data, since there are so many variables...hand warmth etc.
Submitted by: Lulu Lemon on 18 December 2008
Results?
Submitted by: dude on 18 December 2008
good starting point for anyone doing this recation
Submitted by: alia on 17 November 2008
It is the best thing I have ever seen in my whole entire life
Submitted by: aliba on 27 November 2008
I am a teacher of chemistry teaching in college, I would like to increase my experimental knowledge with you.
Submitted by: Dr Santosh on 14 January 2009
Good start for people who don't no how to start.
Submitted by: moahib on 14 January 2009
:) nice
Submitted by: juris on 27 January 2009
Great! But maybe you should try this experiment with a divider in between, so that exactly when the reaction metal and acid meets, the timer can be started, without having any hydrogen escape! :)
Otherwise... very well done! I am doing this in class tomorrow, so thanks for the help!
Submitted by: riski on 20 February 2009
i did not find this useful and to be honest my theory of quantum physics is a lot easier to understand . sort it out . now
Submitted by: crazy clowrey on 20 February 2009
Ok. Not good for homework help.
Submitted by: Kaktus on 20 February 2009
I think this was very useful and that it helped me with my coursework so I dont like the fact that people are saying stupid stuff about it.
Submitted by: fatima on 18 March 2009
This experiment seems quite straightfoward. However, my concerns are whether or not it's going to be suitable for an A2 student's individual investigation?? As many of the comments I looked at above state how it's a "Good experiment for practical data analysis GCSE coursework".
Submitted by: fateh on 18 March 2009
Thank you so much this helped a lot as I'm doing a similar investigation in science. But can I just ask whether you are investigating the factor that the increase in temperature would have?
Submitted by: Sasuke! on 18 March 2009
Thank you so much! But can I just ask whether this method will be compatible with the reaction, Calcium carbonate + Hydrochloric acid -> Calcium chloride + Hydrogen as opposed of using magnesium ?
Submitted by: Sasuke! on 18 March 2009
its no good for homework help!
Submitted by: nikky on 18 March 2009
I want a chemical reaction whereby there is zinc and hydrochloric acid, The experiment must be measuring the rate of reaction.
Submitted by: Sihlalo Eleki on 8 April 2009
A great starter experiment to get the pupils thinking about rates.
Sasuke! Calcium carbonate produces carbon dioxide, calcium chloride and water in your case but you could use the experiment in the same way.
Submitted by: shayno on 26 March 2009
What of the results to this experiment?
Submitted by: Jack Smith on 26 March 2009
I think this website has really been helpful. It gave me some extra information that I needed for my GCSE science coursework, so thank you for uploading it.
Submitted by: sarah ali khan on 8 May 2009
Really helped me as im in yr 10 at school and my chemistry teacher is not helping me whatsoever, so thanks a lot - you have helped me so much.
Submitted by: chemistry on 8 April 2009
Observations???
Submitted by: zzz on 22 July 2009
It's quite ideally good. But students who will attepmt doing such an experiment should be more vigilant and careful on whatever happens unexpectedly.
Submitted by: mon on 22 July 2009
It helped but I'm doing this experiment I think but I'm only in year and we have to do a whole project on it. I don't understand because ares as about increasing the moles. Plz help me:)
Submitted by: naomi on 14 August 2009
Naomi, this site is mainly for teachers - it would be better to try the 'Re:act' website which provides help for chemistry students at www.react-chemistry.org. It has lots of information and advice on projects (investigations) like the one you have to do.
Submitted by: Faraday on 14 August 2009
its good for GCSE work, although our school uses calcium carbonate instead of magnesium and we tend to use gsa syringes or balances to measure rate
Submitted by: stephen pester on 27 November 2009
This was helpful for my science coursework,thanks,but I was disappointed that there weren't any results shown.
Submitted by: nitharsi on 10 December 2009
Results would have been great with dummy data as I really wanted to find out how long it takes for magnesium to react completely with the hydrochloric acid.
Submitted by: Y2YakaAwEsOmE on 18 January 2010
Discussion??
Submitted by: meen on 22 January 2010
Thank you - that really helped me :)
Submitted by: mariam jamjoom on 7 February 2010
Anybody know how the volume of gas produced relates to number of moles?
Submitted by: Abiii on 28 February 2010
This really helped!
Submitted by: ad on 5 March 2010
Good!
Submitted by: henry on 8 March 2010
Very nice experiment for those who are at GCSE level.
Submitted by: Jet on 10 October 2007