Mabag, Viannery D., Mangune, Paolo D.
Chem 14.1, MAB1, Ms. Angelyn del Rosario
March 8, 2010
The experiment allowed students to explore different electrolytes and classify them into acids, bases and salts by using different indicators or by measuring the pH levels of each. The experiment also helped students classify different substances through their conductivity properties. The preparation of a 1 M stock solution from NaOH pellets diluted to a 0.1 M NaOH solution was also utilized in making the students understand the concept of titration. Using 0.1 M NaOH as a standard solution, the concentration of an unknown acid was calculated from the endpoint of an acid-base titration.
II. Keywords: acid, base, salt, pH, electrolytes, conductivity, titration
The experiment made the students classify substances as acids, bases, and salts using different indicators; identify pH; classify electrolytes as weak or strong based on conductivity; prepare 1 M NaOH from NaOH pellets; prepare 0.1 M NaOH from 1 M NaOH; determine endpoint of an acid-base titration; and calculate the concentration of an unknown acid solution based from titration data. Electrolytes are substances that dissociate into ions when dissolved in water. They are classifiable into acids, bases and salts using different indicators. An acid releases hydrogen ions, donates protons and accepts electron pairs. It is usually sour in taste and reacts vigorously with most metals. It also changes blue litmus paper to red. Moreover, it has a pH less than 7 and can be used to neutralize bases. A base, on the other hand, releases hydroxyl ions, accepts protons and donates electron pairs. It usually has a bitter taste and is nonreactive to metals. It has a pH more than 7 and changes red litmus paper to blue and can be used to neutralize acids. Salts result from the neutralization of an acid with a base. There are different indicators used to classify electrolytes. Litmus paper, most of which, turns from blue to red with acids and red to blue with bases. Phenolphthalein changes from colourless to pink at a pH range of 8.0 to 9.8. An acid gives a clear color with phenolphthalein while a base gives a reddish violet to pink color. Congo red changes from blue to red at a pH range of 3.0 to 5.0. With Congo red, acids give a blue color while bases give red. The pH paper gives the exact pH of a substance through the different colors of its layers. The pH scale is logarithmic and as a result, a whole pH value below 7 is 10 times more acidic than the next higher value. Conductivity determines the extent of dissociation of a solute therefore classifying them as strong or weak electrolytes and non-electrolytes. Electrolytes conduct electricity while non-electrolytes do not, since they do not dissociate into ions when in a solution. A preparation of a diluted solution involves adding more solvent to a solution. In this experiment, dilute solutions are prepared from a stock solution. Titration was used to determine the concentration of an unknown acid. In the process, small amounts of the standard solution are added until the endpoint is reached. This is determined by the change in color of the indicator used. From the volumes of the unknown acid and the standard solution, the molarity (M) was calculated.
In this experiment, different electrolytes are classified into acids, bases and salts. 5 drops of 0.1 M solutions of NaOH, NH4Cl, HCl, HC2H3O2, NaCl, C12H22O11 and distilled water were tested with litmus paper, phenolphthalein and congo red to classify them. Colors of each were noted. The pH of the solutions were also taken using pH paper. Afterwards, 1 mL of 1 M HCl and 1 M NaOH were mixed in a test tube. This mixture was tested with available indicators. The procedure was repeated using 1 M acetic acid in place of HCl. The conductivity test was performed to determine...