Magnesium and Hydrochloric Acid Lab

Jack Murphy

Andre Stetser

5210-1

Abstract: By inducing a chemical reaction by subjecting a strip of magnesium to hydrochloric

acid, the density of the hydrogen gas emitted can be acquired through a series of calculations. To

determine the density, you would first find the moles actually produce by using the Law of

Partial Pressure and the Ideal Gas Law. Find the Volume for that amount of moles at STP. Then

take that amount of moles and convert to grams. Divide the grams by the Volume at STP and

you have the density of H2 gas at STP.

Objective: The purpose of this lab is to calculate the number of moles and the density of the

hydrogen gas produced when hydrochloric acid and a strip of magnesium react with each other

in a controlled environment. The controlled environment is the distilled water because it reduces

extraneous reactions as well as allows us to start with no gas and let the H2 rise to the top of the

tube to fill it. The lab will utilize the means of the use of equations, such as Daltons Law of

Partial Pressure, and the Ideal Gas Law, in order to determine the density. The lab will connect

many processes, which may have been separate ideas from before, and force the experimenter to

utilize all of the knowledge that he/she possesses in order to calculate the density of the hydrogen

gas produced. The calculation of the number of moles of the hydrogen gas in the eudiometer is a

secondary goal of this lab and is necessarily in the calculation of the density.

Introduction: The simple reaction between 2 separate substances (Mg and HCl) gives the

experimenter a solid grasp on how different factors, such as temperature, volume, and density

affect each other in this demonstration. This lab teaches the experimenter to perform good

observation taking as well as data management. The experimenter learns to keep track of his

work and to write it in a clear and concise manner. This work should be given much attention,

especially in schools, because it will give the new scientists a solid introduction and viewing of a

reaction in progress and an understanding of pressure as well as equilibrium. This should be

given the financial ability to be publicized in many institutions of learning, for it clearly shows

an introduction into the world of chemical reactions and utilization of formulas of pressure.

Theory: The final result we wish to find is the density of the hydrogen gas. Since the

“universally accepted” results of densities of gases are recorded at STP and in g/L, we will have

to convert our units. It is crucial that the experimenter must have a full grasp on many concepts

pertaining to mass, volume, etc. in order to fully achieve the accurate data. The universally

“accepted” results would be the discernment of the number of moles of hydrogen gas in the

eudiometer that is within a 10% error yield of the theoretical yield which can be produced if all

conditions are right and a density of H2 gas at STP of .0899g/L.

Procedure:

Equipment

Beaker

Eudiometer

Hydrochloric Acid

Magnesium Strip

Rubber Stopper/ String

Squeeze Bottle

Stand with Clamp

Schematic

Method

First, we received a strip of Mg and weighed and recorded its weight in grams. We then tied the

magnesium strip onto the stopper using the little piece of string. We filled up the beaker about

2/3 full with tap water. We measured the tap water, and then recorded the temperature of it using

a thermometer. We then acquired the distilled water, placed it into the squeeze bottle for

transportation, and used the thermometer to record the temperature of it. After this was done, we

firmly attached the eudiometer on the ring clasp and stand, and poured about 10mL of 6M

hydrochloric acid into it. Using the squeeze bottle, we filled the rest of the eudiometer with

distilled water to the very lip so that when the stopper is placed in, water will be pushed out. This

is done so that no outside gas is recorded in our calculation. After this was done, we recorded the

temperature of the mixture in the eudiometer using the thermometer. This will be the temperature

to base the water vapor pressure from. Next we plugged the eudiometer with the rubber stopper

and string and made sure the Mg was inside the tube. Then we loosened the grip of the ring,

placed our thumb over the hold of the rubber stopper, flipped the eudiometer upside down, and

placed the top with the magnesium strip tied to the stopper into a beaker filled with tap water and

removed our thumb. As we waited for the magnesium strip to dissipate, we recorded the pressure

and temperature of the room. When the magnesium strip finally fully disappeared, we recorded

the volume of the gas left in the eudiometer after flicking the tube to get all the bubbles off of the

sides (which is impossible).

Results:

1. Table of all the Starting Data

Mass of Mg strip (in grams)

Volume of HCl(in mL)

Tap Water Volume(in mL)

Tap Water Temp.(in °C)

Distilled H2OTemp.(in °C)

Eudiometer Temp.(in °C)

Pressure of Room(in Hg)

Temp. of room(in °C)

Final Volume of H2 Gas(in mL)

.06

.002mol *A mol

10 1300 20.3 19.6 20.3293.3K *B

31.01 21294K

55.8

2. Table of the Pressures in the Experiment

Barometric Pressure of Room Water Vapor Pressure Pressure of H2 Gas

31.01 in Hg 17.5 mm Hg -----------------------------------

1.04 atm *C 2.3 X 10-3 atm *F 1.01 atm *H

* any letter with an asterisk before it indicates a more exact value is kept track of in the calculator for future calculations. These letters are in place for the whole exact number and may be used in later calculations.

3. Table for the Ideal Gas Law

Pressure of H2 Volume of H2 Number of Moles of H2

Universal Gas Constant

Temperature of H2

1.01 atm *H 0.0558 L *E 2.34 X 10-3

same as Mg*A

0.082058 L atmmol K

293.3 K

4. Table for the Calculation of the Density

Pressure of H2 Volume of H2

At STPNumber of Moles of H2

Universal Gas Constant

Temperature of H2

1.01 atm same as*H

5.26 X 10-2 L*I

2.34 X 10-3 0.082058 273.3

5. Table for the Theoretical Yield, The Experimental Yield, and the Percent Error

Theoretical Yield Experimental Yield Percent Error

2.47 X 10-3

*A2.34 X 10-3

*H4.83%

6. Table for the Calculation of the Mass of the Hydrogen

Mass (in g) Volume (in L) Molecular Mass

4.74 X 10-3 g*J

5.26 X 10-2 L*I

2.015882(1.00794)

Interpretation of Results: Throughout the course of this experiment, there were many different

factors and equations which have been used to determine density of the hydrogen gas. The data

present in Table 1 is self-explanatory, and shows the preliminary data which is acquired during

the course of the experiment. Table 2 requires the production of the pressure of the hydrogen gas

by subtracting vapor pressure of water from the room. A miscalculation could be created if you

do not convert the units to atmospheres. The following equation should look as such.

Partial Pressure Law = Ptotal = Pvapor + PH2

Solve for PH

PH = Ptotal - Pvapor

(31.01 in Hg X 0.0334 atm

1∈Hg) - (17.5 mm Hg X

1 atm760 mm Hg

) = *G atm

Ptotal - Pvapor = PH

Take note that the conversion factor from in Hg to atm is the multiplication of the starting factor

with 0.0334; the conversion factor from mm Hg to atm is the division of the starting factor by

760. Take heed that when the table states approximately, this is saying that for writing purposes

significant figures have been used in order to make this fit on the computer. DO NOT use

significant figures until the very last calculation has been acquired. Next, we have to find the

number of moles present of hydrogen gas. The format should use the Ideal Gas Law to acquire

the number:

PV=nRT

Make sure that the starting equation is correct. When finding the number of moles, the starting

equation should be as such:

n=PVRT

The first step in using the Ideal Gas Law is to convert all the numbers to their respective unit:

55.8 mL X 1000 = 0.0558 L; 20.3 °C + 273 = 293.3 K

Make sure that R is the Universal Gas Constant:

0.082058 L atmmol K

Now that we have acquired all the needed data in their respective unit form, we can now plug

and chug.

n=(0.0558)(¿G)

(293.3 )(0.082058)

n= 2.35 X 10-3 *H

This represents the number of moles of hydrogen gas which are actually contained in the

eudiometer. This will be used to represent the experimental yield. The theoretical yield

V=nRT

P

V=D (0.082058 )273

1 Determine Volume at STP

V=5.25 X 10-2 *I Volume at STP

Now we must find the experimental yield through molar ratios.

Mg + 2HCl MgCl2 + H2

Mg:H2 is a 1:1 ratio

Next we must determine the number of moles of Magnesium, which will be equal to the number

of moles of H2 gas.

.06 g Mg X 1mol

24.3050 g Mg = 2.47 X 10-3 mol *A

A−HA

X 100% = 4.83% The percent error // We calculated that we were missing about 2.8

mL of H2 which could easily be explained by the extraneous bubbles stuck to the sides of the

tubes. Now, we need to find the amount of grams of H2 for the density.

M = mol(molar weigh)

*H x (2(1.00794)) = 4.98 X 10-3 g *J

Now we must determine the density which is mass per unit volume

D=mV

D =JI

=8.99 X 10-2 gL

This is extremely important because this precisely matches the universally accepted results

The density of the gas in our experiment without STP is:

D = JE

= 8.48 X 10-2 g/L of H2 gas at 293.3K and 1.01 atm of H2

One major keynote that you want to be aware of is to never use significant figures until the very

end of the calculation. If you have put any miscalculations or errors, make sure to record them.

Always be careful when attaching the magnesium strip on the string to the stopper, for if the

magnesium floats up to the top of the eudiometer and does not stay attached to the stopper, you

will have to redo the experiment. Make sure that the stopper is completely on and secure before

flipping the eudiometer upside-down into the distilled water, for if the plug comes out and

releases the tube’s contents into the distilled water, you will have to redo the experiment. Always

make sure that when you are recording a calculation to convert your data to the right unit (i.e.

mL to L, °C to K, etc.). If you are concerned about any of the calculations concerning the

number of moles, make sure to note that because it is universally accepted that the pressure

inside of the eudiometer is equal to the external pressure, it is possible to determine the number

of moles present in the tube after using the partial pressure of gasses to eliminate the pressure of

the water vapor. This means that the pressure of the hydrogen and the water vapor combined is

equal to the barometric pressure outside the eudiometer (the pressure of the room) minus the

water vapor pressure. When undertaking the process of filling the eudiometer containing the

hydrochloric acid with water, make sure that you are filling it with distilled water, NOT the tap

water. Distilled water diminishes all chances of having extraneous reactions with the

hydrochloric acid that are not desired. This will be a huge difference in calculations, which you

will discern at the end of the experiment.

Conclusion: Through this experiment, we have tested the process in which the density of a gas

can be acquired through the undertaking of a chemical reaction, in this case, one between

hydrochloric acid and magnesium. The final density that we acquired is 8.99 X 10-2 gL

. This is

exactly the accepted result, which shows our lab was a success. The process of this experiment

may be used in the future for testing chemical reactions on a much larger scale. The number of

moles produced was also within the universally “accepted” ten percent error margin. The same

process can be done for pharmaceutical or nuclear testing, and while the actual variables and

elements used in the experiment may change, the formulas and equations may not.