Answered: In this lab, you are producing hydrogen…

Chemistry

10th Edition

ISBN:9781305957404

Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste

Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste

Chapter1: Chemical Foundations

Section: Chapter Questions

Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...

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Calculating Avogadro’s Number Using Electrochemistry
Background
As discussed in lecture, electrochemistry allows stoichiometric calculations to be related
to current and time, if a chemical equation that relates electrons to reactants and products is
known. Recall that electrolysis involves using an electrical current to decompose a compound
into simpler substances. This particular experiment will involve the electrolysis of a sulfuric acid
solution to generate hydrogen gas. By measuring the amount of hydrogen produced by the
current and length of time of the electrolysis, it is possible to calculate a value for the Faraday
constant and thus also Avogadro’s number. The amount of hydrogen is determined by utilizing
the ideal gas law (PV = nRT) to determine the number of moles of hydrogen produced in the
electrolysis.
The amount of charge that has passed through the solution is measured in coulombs
(C). It is calculated by measuring the current (in amperes, A) that has passed through the
solution over a known time. Once the charge is known, it is possible, by knowing the amount of
hydrogen produced and the stoichiometry of the reaction, to determine Faraday’s constant (the
charge in coulombs, C, on one mole of electrons). Furthermore, since the charge of one
electron is known (1.60 X 10-19 C) Avogadro’s number can likewise be calculated.
Procedure
Set up the apparatus as shown on the demonstration table.
Place 100 mL of deionized water and 50 mL of 1 M sulfuric acid in a 250 mL beaker. Fill
the gas buret completely with this solution and invert it as demonstrated. Making sure that the
DC source is unplugged, attach a copper wire to the negative terminal of the DC source and
place the other end into the inverted mouth of the gas buret. Be certain that all of the
uninsulated wire is inside the buret so that all of the hydrogen is collected. Another copper
wire is simply immersed in the solution in the beaker. Read where the top of the solution is in
the buret and record this value.
Call your instructor to plug in and turn on the DC source, as you begin timing. Record
the current (it should start at approximately 0.20 amperes) every thirty seconds so that an
average current can be calculated. Do not touch the apparatus while it is plugged in! Continue
the electrolysis until at least 10 mL of hydrogen have been collected. Note the time and unplug
the DC source. Record the actual volume of hydrogen.
Measure the height (in millimeters) of the solution column in the gas buret above the
solution in the beaker (i.e. the distance from the top of the solution in the beaker to the top of
the solution in the column). Also, measure the temperature of the solution and determine the
air pressure in the room.

Lab question 1: In this lab, you are producing hydrogen gas in an electrolytic cell. Provide the balanced half reaction for this process? If a student performs this lab and isolates 4 moles of hydrogen, how many moles of electrons were consumed? If the student calculates that 800000 coulombs of charge were consumed in the production of the 4 moles of hydrogen mentioned above, what is his experimental value for Faraday's constant (the charge on one mole of electrons)?

Definition Definition Law that is the combined form of Boyle's Law, Charles's Law, and Avogadro's Law. This law is obeyed by all ideal gas. Boyle's Law states that pressure is inversely proportional to volume. Charles's Law states that volume is in direct relation to temperature. Avogadro's Law shows that volume is in direct relation to the number of moles in the gas. The mathematical equation for the ideal gas law equation has been formulated by taking all the equations into account: PV=nRT Where P = pressure of the ideal gas V = volume of the ideal gas n = amount of ideal gas measured in moles R = universal gas constant and its value is 8.314 J.K-1mol-1 T = temperature

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