Universal Gas Constant Lab Essay

Quantitative Observations:

Volume of HCl(aq) used = 10cm3

Concentration of HCl(aq) used = 3M

Required Mass of Mg(s):

Mg(s) + 2HCl(aq) � MgCl2(aq) + H2(g)

P(H20) (at 24C) = 3.0 kPa

P(H2) = Ptotal – PH20

= 107.3-3.0=104.3kPa

Volume of H2(g) = 45cm3 = 0.045dm3

Number of moles of H2(g) = (0.045/24) = 0.001875moles

Ratio of Mg(s) to H2(g) = 1:1

=> 0.001875 moles of Mg(s)

=> 0.001875 * 24.305 = 0.0455g � 0.04g

Universal Gas Constant: P.V = n.r.T � r = (P.V)/(n.T)

=> R = (104.3 * 0.045)/(0.001875 * (24.5+273)) = 8.41 K-1 mol-1

=> Percentage Error = {(8.41-8.31)/8.31} * 100 = 1.2%

Qualitative Observations:

* Colorless gas bubbles observed.

* Concentration swirls observed.

* Significant effervescence noticed close to the magnesium ribbon.

* Colorless gas produced slowly then almost instantaneously the rate at which the colorless gas is being produced speeds up rapidly.

* Eudiometer warms up slightly during the reaction.

* Droplets observed above the liquid, also some droplets on the sides of the eudiometer.

* The magnesium ribbon diminishes in size.

* The magnesium ribbon gets shinier and looks cleaner.

* Hydrochloric acid is also noticed flowing out from underneath the eudiometer.


The literature value of the universal gas constant is 8.31 K-1 mol-1 and my value is 8.41 K-1 mol-1, which implies that the percentage error of my experimental gas constant is 1.2%. Under the conditions in which the experiment was performed, my results are acceptable because very little errors where encountered and the the percentage error is very small. Also due to the fact that the experiment was conducted under the same room temperature and pressure and the same mass of magnesium was used for each trial. A random error which I believe might have affected my result was the droplets noticed on the sides of eudiometer and this is an error because it’s meant to just be the hydrogen gas present there, not the gas and the droplets.


Errors, Observations during the Experiment

Effect on the experiment / Explanation

Concentration swirls observed during the reaction

This is caused due to the difference in densities between the liquids initially mixed in the solution

Effervescence noticed close to the magnesium ribbon

This effervescence observed is due to the colorless hydrogen gas being produced as magnesium reacts with the hydrochloric acid

Rate of the production of the colorless gas suddenly speeds up

This is because when the eudiometer is turned upside down, it takes a bit of time for the hydrochloric acid to fully get in contact with the magnesium ribbon. This is because not all the hydrochloric acid flows straight to the magnesium ribbon immediately

Exothermic Reaction

This is because the products made are more stable than the reactants, because the bonds made are stronger than the bonds broken. Also all neutralization reactions release heat energy because they are exothermic

Droplets noticed above the liquid; where the gas should be present and also some droplets noticed on the sides of the eudiometer

This indicates that the eudiometer is not totally clean, thus these droplets form around the impurities. An example of an impurity could be dust particles

The magnesium ribbon gets smaller in size and looks cleaner

This is because as the magnesium reacts with the acid, the metal turns into ions into the solution, thus the metal loses its mass

Hydrochloric acid flowing out from underneath the eudiometer

This is caused because hydrochloric acid is being displaced as the eudiometer is filled with hydrogen gas

Incorrect readings taken

This could lead to me having written down incorrect data which affected my final gas constant and led to my 1.2% error difference


* One major thing that I would do to improve the investigation would be to do more trials for the experiment, thus to reduce the random errors.

* To clean the eudiometer very well, and ensure that there’s as little as possible dirt and impurity present in the eudiometer.


IB Chemistry. (2009). Course Details, Data Booklet and Internal Assessment Related Documents.


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