Chemistry 1151 Laboratory
Analysis of acid by titration with sodium hydroxide
Introduction: The purpose of this experiment is to demonstrate an example of how to determine the unknown molarity of hydrochloric acid by titration with a base (sodium hydroxide). Titration is a common laboratory method of quantitative chemical analysis that is used to determine the unknown concentration of an identified analyte (wekipedia). The first step will be measuring and combining water and acid (Hydrochloric acid). An indicator anthocyanin will be added to the solution to change the color to pink. Anthocyanin is a water-soluble vacuolar pigment that may appear red, purple, or blue depending on the pH (Wikipedia). This pink color acts as a pH meter and will show a change in color to represent a change in the pH. As the base (sodium hydroxide) is added, the solution will then change color (this is referred to as the “stoichiometric end point”). This color change represents the increase of pH, as well as showing that the moles of the acid in the solution are equal to the moles of the base (Survey of Chemistry lab manual). Using a dilution equation of M1xV1=M2xV2, the concentration of the hydrochloric acid can be calculated. M1=NaOH(molarity), V1=NaOH(volume), M2=HCl(molarity), V2=HCl(volume). Procedure:
Instructions for laboratory were found on page 91 of Survey of Chemistry lab manual. All calculations were rounded off by 2 decimal places for accuracy. Preparation of the indicator required a combination of 50 grams of cabbage with 50ml of ethanol and 20mL of DI water to extract the anthocyanin indicator. This procedure was completed by the instructor and the anthocyanin indicator (“cabbage extract”) was provided. Then 10mL of hydrochloric acid and 20mL in of deionized water were measured in a graduated cylinder and combined into an Erlenmeyer flask. Pipette 5 to 10 drops of anthocyanin indicator was added to the...
References: Survey of Chemistry lab manual, “Chem 1151 Laboratory Experiments 3rd edition 2011-2012”
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