Standardization of Acid/Base

Topics: Sodium hydroxide, Chemistry, Titration Pages: 6 (1558 words) Published: October 7, 2012
Eunice Ivy B. Gamboa
Solutions of known concentration are prepared by dissolving measured masses of standard acids in distilled water. The concentrations of unknown solutions of sodium hydroxide are determined by titration. An acid solution reacts with a base solution in a "neutralization" reaction. Titrations permit the concentrations of unknown acids/bases to be determined with a high degree of accuracy. In order to analyze unknown acids/bases, we must have a "standard" solution to react with the unknowns. A standard solution is one in which the concentration is known accurately. We will first prepare a standard solution of NaOH. One way to prepare a standard solution is to dissolve an accurately massed amount of the substance and dilute it to a measured volume. In this way; the concentration can be calculated exactly. However, it is usually impossible to obtain NaOH of sufficient purity to use it as a primary standard. An indirect method is more practical for obtaining a standard solution of NaOH. We will prepare a solution of an approximate molarity and standardize it against a primary standard of known purity. KEYWORDS


Jeanett Daza
Leones Galicia

This experiment will introduce you to the analytical method of volumetric titration. This method is a quantitative analysis of liquid or solution by comparing the volumes that react with known values of standard chemical solution. Solid sodium hydroxide is hygroscopic, which means that it absorbs moisture from the

September 24, 2012

atmosphere. Once it has a little moisture it also absorbs carbon dioxide which is always present in air. Standardization is the process of determining the exact concentration (molarity) of a solution. Titration is one type of analytical procedure often used in standardization. In a titration, an exact volume of one substance is reacted with a known amount of another substance The point at which the reaction is complete in a titration is referred to as the endpoint. A chemical substance known as an indicator is used to indicate (signal) the endpoint. The indicator used in this experiment is phenolphthalein. Phenolphthalein, an organic compound, is colorless in acidic solution and pink in basic solution. This experiment involves two separate acid-base standardization procedures. In the first standardization the molarity of a sodium hydroxide solution (NaOH) will be determined by titrating a sample of potassium acid phthalate (KHP; HKC8H4O4) with the NaOH. In the second procedure the standardized NaOH will be used to determine the molarity of a hydrochloric solution (HCl) II. EXPERIMENT METHODOLOGY

A. Standardization of NaOH

H20 1L bottle 17ml NaOH

0.4 g

2-3 drops of phenolphthalein

B. Determination of purity of KHP
* Repeat steps 1-5 for impure KSP
C. Standardization of HCL
Measurement| 1st trial V-of titrant(ml)| 2nd trial V-of titrant(ml)| 3rd trial V-of titrant(ml)| Average(ml)| Pure KHP| 16.70| 14.70| 18.10| 16.50|
Impure KHP| 16.10| 12.10| 15.80| 14.66|
HCl| 12.90| 12.20| | 12.55|
Given units/initial values| M| ml| G| |
KHP| | | 0.40| |
NaOH| 0.60| 17.00| | |
HCl| 0.10| 15.00| | |

25ml HCl Distilled h20

III. Data and Results

(g) of KHP__ = ___mol________ = M
Mwt. Of KHP(L) of used titrant
Trial 1
0.4 g_____ = 1.9607 10-3mol = 0.1188 M
204g/mol0.0165 L

(g) of KHP = (M)(V)-titrant
Mwt. Of KHP
= (0.1188 M) (0.0146 L) x 204 g/mol
= 0.3538 g
%purity = g KHP_____ x 100
(g) impure KHP
= 0.3538g x 100=88.45 %
M1 = (M2) (V2)
= (0.1188 M) (0.0125L)
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