Standardization of a Sodium Hydroxide Solution and Acid-Base Titrations Purpose

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Standardization of a Sodium Hydroxide Solution and Acid-Base Titrations Purpose The purpose of this lab is to standardize a prepared sodium hydroxide solution, and to use the standardized solution to determine the molarity of an unknown acid Introduction Chemical reac chemical interactions, acids and bases react with known stoichiometric ratios based on the coefficients of the balanced chemical reactions. For example, the reaction of the strong base NaOH and oxalic acid is: tions between acids and bases are commonly encountered in chemistry. As with other 2NaOH (aq) + H2C20, (s) NazC204 (aq) + 2H20 (1) In this example, two moles of NaOH are required to react completely with one mole of oxalic acid Knowing the stoichiometric ratio of an acid-base reaction allows for the determination of an unknown concentration, assuming that the reaction has gone to completion, and the number of moles of one of th e components is known. One way to determine the change in concentration of an acid or base is to use the pH scale. The pH scale measures the degree of acidity or alkalinity in a solution, and can be calculated using the following formula: ho the degre of acidity or alkalinity na pH =-log[H+] an acidic compound interacts with a basic compound, the concentration of hydrogen ions decreas eading to an increase in the pH of the solution. A pH meter can be used to accurately and rapidly measure the pH of a solution. rogen ions decreases itrations are a common technique used in laboratories to determine the quantity of one reactant when he other one is known. Titration curves commonly plot volume of the titrant (the solution delivered by buret) on the x-axis and pH on the y-axis. In most cases, titrations are performed with a basic solution dded to an acidic solution (although identical results are obtained if the inverse is performed). As base s added to the acidic solution, the pH of the solution increases. The increase is gradual at first, and ncreases sharply as the equivalence point is reached. The equivalence point in a titration is the point at vhich an equivalent number of moles of acid and base have reacted, according to the balanced chemical eaction. The equivalence point represents the point during the titration where the rate of change in pH sthe greatest. As additional base is added, the rate of change decreases and eventually will level out. this experiment, a solution of NaOH will be prepared and standardized. Standard solutions are knowrn o a high level of accuracy (usually four significant figures) and can be prepared in two ways. With the irect method of standardization, a known amount of a primary standard (known to have an extremely igh purity) is dissolved in a known volume. With the indirect method of standardization, a solution of pproximately known concentration is prepared and standardized against a primary standard. Solid odium hydroxide readily absorbs moisture and carbon dioxide from the air; therefore, the amount of NaOH in solid form cannot be accurately determined. For this reason, an indirect method of standardization must be used for this experiment. The primary standard that will be used for this experiment will be potassium hydrogen phthalate, or KHP. KHP (molecular formula KHCgH0) will rea with NaOH via the following equation: n order to be sure of the obtained molarity for the NaOH solution, titrations must be performed in riplicate. For this experiment, the solution will be deemed standardized when a relative average viation (RAD) value of 20.0ppt or less is obtained. This requirement ensures that the precision of the itrations are acceptable for future experiments. Once standardized, the NaOH solution may be used tc trate other acidic solutions in order to determine the molarity of an unknown.

Explanation / Answer

1)    NaOH + HCl -------------> NaCl + H2O

a) NaOH and HCl will react each other at 1:1 ration by moles.

2) The best way to precisely measure 10.00 mL of a solution is pipette out the solution by using a 10.mL volumetric pipette.

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