The Mass of Acetylsalicylic Acid in Aspirin
The purpose of the lab is to determine the mass of the ‘active ingredient’ in a commercial ASA tablet. -------------------------------------------------
There are three main theories surrounding acids and bases including the Arrhenius, Bronsted-Lowry, and Lewis theories. The Arrhenius theory of acids and bases states that acids produce hydrogen ions (H+) in solution while bases produce hydroxide ions (OH-) in solution. Arrhenius was able to determine his theory based on his prior knowledge of the behaviour of substances in aqueous solution. Arrhenius went further to describe strong acids as a strong electrolyte that was able to ionize completely in order to give hydrogen ions in aqueous solutions. However weak acids can only ionize partially, remaining moderately in molecular form. Similarly, a strong base is also a strong electrolyte that ionizes completely to release hydroxide ions in aqueous solution while weak bases only partially ionize. The Arrhenius theory is specifically deals with acid-base reactions in water. The second theory, intends the contemporary ‘protonic’ or Brownsted-Lowry theory of acid-base behaviour. This theory states that an acid is a compound or ion that can give up a proton however a base is a compound or ion that accepts a proton. Water is amphiprotic because water can give up and accept proton depending on the reaction. Water gives up a proton to form hydroxide ions (OH-) but water accepts a proton to form hydronium ion (H3O+). The Bronsted-Lowry theory is just an addition to the Arrhenius theory in term of all Arrhenius bases that are sources of hydroxide will accept protons. Bronsted-Lowry theory also coincides with the ability for ammonia and amines to accept protons to form ammonium ions and it can also be applied to reactions that involve solutions that do not have water as its solvents. The last theory, the Lewis theory of acids and bases, claims that acids accept electron-pairs while a base donates electron-pairs. The Lewis theory is useful to explain organic reactions. An example of this theory is the base H3N which has a lone pair. So according to the theory, this base will donate the electron pair to a proton when forming the acid NH4+.
Titration is a method used to identify the exact concentration of an unknown solution by way of a chemical reaction. The molarity of acidic or basic solutions can be used to switch to and from moles of solutes and volumes of their solutions. Titration is performed when solution 1 is added to solution 2 until a chemical reaction between the solutions is visible. Solution 1 is called the titrant and solution 1 is said to titrate solution 2 at the completion of the reaction. The endpoint of titration is determined by a change of color which is a result of indicator added to solution 2. Assuming solution 2 is the acid, as long as there are excess H+ ions in the solution, the solution remain acidic. The indicator also stays mostly in acid form so the acid-indicator solution is colorless. However when enough base solution is added to react with the H+ ions the reaction is complete, the endpoint has been reached. However if even a drop more of base is added into the acid, there is now excess hydroxide ions in the solution. The OH- ions of the base that has been added to the acid reacts with the indicator changing the indicator from acid to base. When using phenolphthalein as indicator, for example, the base form for this indicator is red. In this case when the indicator changed into base form, the solution turns red indicating the reaction is complete. Observing the amount of solution 1 used to titrate solution 2 and the knowledge of the concentration of solution 1 and the volume of solution 2 used, the concentration of solution can be identified.
Neutralization reaction is the acid...
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2. "Neutralization reaction." Connexions - Sharing Knowledge and Building Communities. N.p., n.d. Web. 28 May 2010. <http://cnx.org/content/m17138/latest/>.
3. "Phenolphthalein." Digipac Microcomputer Software. N.p., n.d. Web. 28 May 2010. <http://digipac.ca/chemical/equilibrium/phenolpthalein.htm>.
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