Summary:
Experiment to distinguish the difference of acids and bases and to found out what substances are acids and which are bases.
1.) Purpose - The purpose of the experiment was to classify biological solutions as acids or bases and to measure the pH of a solution while learning to relate the pH scale to how acidic or basic a solution is, and learning to explain how a buffer affects the pH of a solution.
2.) Materials - For part one the materials are distilled water, tap water, ammonia, baking soda, vinegar, shampoo, orange juice, milk, bleach, diet coke, full-range pH paper, 10 test tubes, distilled water in wash bottle, biceps, pencil, test-tube rack, computer pH tester, and red and blue litmus paper. For part two the materials are Bromothymol blue indicator, egg white solution, 125-mL Erlenmeyer flask, 0.1 N Hydrochloric acid, dilute basic solution, medicine dropper, computer pH tester, and biceps.
3.) Procedure - Part I
- Labeled 10 test tubes so that there is one test tube for each of the substances.
- Poured a sample of each of the ten substances into its corresponding container.
- Used biceps to hold pieces of pH paper under the different samples and recorded the pH level of each substance on the data chart.
- Tested all substances with red and blue litmus paper and recorded the results on the data chart.
- Rated each substance in having either a high, low, or medium concentration of H30+ and then classified each substance as an acid, base, or neutral.
- Used the computer to test the pH level of each substance and recorded the mean of the pH readings on the data chart.
Part II
- Filled a 125-mL Erlenmeyer flask with 25mL of the dilute basic solution.
- Added 4 drops of bromothymol blue indicator and swirled the flask until the indicator was completely dissolved.
- Used computer tester to test the pH level of the substance and recorded the data on the data chart.
- Added 0.1 N HCl drop-by-drops to the solution in the flask until there was a significant color change that did not disappear after thirty seconds.
- Used computer tester to test the pH level of the new solution and record the pH level and the amount of drops needed to change the color of the solution.
- Repeated steps 2-5 using a flask filled with 25mL of egg white solution.
- ) Data Analyze
- Some substances are acids because they form H+ ions in solution. Acids contain a high number of H+ ions. Acids have a pH level that is under seven, the lower the pH level of the substance the more acidic it is.
- Some substances are bases because they produce hydroxide ions in solution. Bases contain a high number of OH- ions and have a pH level of above 7. The higher the pH level of the substance the more basic it is.
- When someone says that distilled water is neutral, they mean that distilled water is neither a base nor an acid. Distilled water's pH level is always 7 because on the pH scale the number seven is neutral.
- An indicator is different form a dye because an indicator changes color depending on the pH of a substance. The color the indicator turns is a direct result of the pH level of the substance tested. A dye changes the color of a substance by adding color. All substances, acids or bases, will turn the color of the dye, and will not differ in color depending on the pH level of the substance.
- The inside of a person's stomach is naturally acidic. When a person eats food the acid helps break down the food. If a person consumes a lot of a highly acidic food a natural buffer will help bring down the pH level in the person's stomach.
- Solution A - pH 10. Solution A has a low concentration of H+ ions, but has a high concentration of OH- ions. Solution A is a base. Solution B - pH 7. Solution B has around the same amount of H+ ions and OH- ions. Solution B is neutral. Solution C - pH 3. Solution C has a high concentration of H+ ions, but has a low concentration of OH- ions. Solution C is an acid.
- Some substances would not change the color of litmus paper because if the litmus paper is red and you are testing an acid then the paper stays red because that is the color that acids turn litmus paper.
- The weakly basic solution needed the least amount of drops to change the color and pH. The egg white solution needed the most drops to change the color and pH.
Data Table I
SubstancepH NumberRed Litmus(red or blue)Blue Litmus(red or blue)H3O+ ConcentrationAcid, Base, or neutral
Demonized Water6redblueFew Acid
Tap Water7redblueNeutralNeutral
Ammonia(NH3)12blueblueA lotBase
Baking Soda9blueblueA lotBase
Vinegar3redredFew Acid
Shampoo4redredFew Acid
Orange Juice3redredFew Acid
Milk7redblueNeutralNeutral
Bleach9blueblueA lotBase
Diet Coke4redredFew Acid
Data Table II
SubstanceInitial pHNumber of drops of HClFinal pH
Weakly basic Solution9.7368.06
Egg white solution11.1768.12
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