|MadSci Network: Chemistry|
Natalie, To understand what is happening in your experiment, it may be necessary to define some of the parameters involved. For chemists, it is necessary to have a unit of reference when dealing with quantities of chemicals. As this reference, Avogadro's constant was chosen and is defined as 6.022 x 10e23 molecules per mol. This means that a mol of any substance always contains the same number of molecules. This is particularly important when we are comparing two different substances that don't have the same molecular weight (also known as molar mass). As an example, if we were to compare 1 gram of NaCl (table salt) and 1 gram of water it would be difficult to tell if there are more salt molecules or water molecules without this frame of reference. For this example, water has a molar mass of 18.01 g/mol and the salt has a molar mass of 58.44 g/mol. n = mass of substance / molar mass Therefore, in our example there would be 0.05552 mol of water and 0.01711 mol of the salt. Molarity of solutions is related to this in that the molarity of a solution indicates the number of moles of solute for every liter of solution. In turn, this can be related to the number of molecules in solution. Now that the basics have been covered, we must now dive into the thick of things and answer the question of molarity effects on rate of electrolysis of HCl. You are correct in saying that the rate of reaction in your case is dependant upon the concentration of the reactant in solution. Every ion in your solution (H+ and CL- in your case) is surrounded by a much greater number of water molecules. When a potential is applied to the electrodes the ions become attracted to the oppositely charged electrode and are drawn through the solution. The ions continue to be drawn until they come in contact with the electrode (this is similar to a person attempting to move toward a door through a crowded room). When contact is made the ion is converted either by gaining an electron or losing an electron. The important part of this is how often an ion comes into contact with an electrode. If there are more ions floating around in solution (in a solution of higher molarity), contact between an ion and an electrode will occur more frequently than in a more dilute solution. This will appear as an increase in the rate of product formation (i.e.: an increase in the rate of electrolysis). I hope that this is what you are looking for. John.
Try the links in the MadSci Library for more information on Chemistry.