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COPYRIGHTFOUNTAINHEAD PRESSDetermining Molar Mass of an Unknown Acid by TitrationObjectives:To learn the technique of titration, and apply it to determine the molar mass of anunknown weak acid by titration with sodium hydroxideMaterials:Three 250-mL Erlenmeyer flasks, one 250-mL beaker, a sample bottle, 50-mLburet, 0.100 M NaOH solution (standardized sodium hydroxide), phenolphthaleinindicator, pH meters, standard buffer solutions (pH = 4.00, 7.00, 10.00, ifavailable), stirring plate with stirring magnet, samples of unknown acidsSafety:Sodium hydroxide solution is very caustic!It can cause skin burns and isextremely damaging if it gets in your eyes.Acid solutions are also corrosive andcan cause irritation if in contact with skin, eyes, and clothing.Always wear safetyglasses when working at the bench with sodium hydroxide or acid solutions.WasteDisposal:All solutions may be washed down the sink with plenty of water at the completionof the titrations.INTRODUCTIONThe determination ofmolar massrepresents an important step in the identification of anunknown substance. There are many methods to obtain this vital information that are related tophysical properties (vapor pressure, osmotic pressure), while others rely on chemical behavior,such as reactions of known stoichiometry. In this lab you will determine the molar mass of anunknown acid based on its reaction with a known quantity of base.The concept of acid-base behavior is one of the most fundamental in chemistry, with importantapplications in biochemistry and industry. There are many ways to define acid-base behavior, butthe most common involves the behavior of a substance in aqueous solution: an acid generateshydronium ions (H3O+), while a base generates hydroxide ions (OH-).Acid:HCl(aq)+ H2O(l)H3O+(aq)+Cl-(aq)Base:NaOH(aq)Na+(aq)+OH-(aq)Acids and bases are characterized asstrongorweak, depending on the extent of ionization. Inthe case of strong acids, such as hydrochloric acid, the acid in solution is completely ionized.For weak acids, such as acetic acid, only a small fraction of the acid in solution forms ions.Strong:HCl(aq)+ H2O(l)H3O+(aq)+Cl-(aq)(~100%)Weak:CH3CO2H(aq)+H2O(l)H3O+(aq)+CH3CO2-(aq)(>5%)For weak acids, equilibrium exists between the undissociated acid (on the left) and the ionizedproducts (on the right). The extent of ionization can be quantified by the acid dissociationconstant, Ka. The expression for Kafor the acetic acid equilibrium can be represented as:

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Term
Winter
Professor
Land
Tags
pH, Sodium hydroxide
We have textbook solutions for you!
The document you are viewing contains questions related to this textbook.
Chemistry & Chemical Reactivity
The document you are viewing contains questions related to this textbook.
Chapter 16 / Exercise 79
Chemistry & Chemical Reactivity
Kotz/Treichel
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