Getting to Know the pH Scale Lab Name: Date: Period: Introduction The pH of a solution is a number which tells us how acidic the solution is. The pH scale is used to measure how many H+ ions are in a solution. pH values can range from 0 to 14, with low numbers (below 7) representing acids and higher numbers (above 7) representing bases. A pH of 7.0 represents a neutral solution. Strong acid Weak acid Neutral Weak base Strong base 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 High hydrogen ion concentration Low hydrogen ion concentration Since acids have high concentrations of hydrogen ions and bases have low concentrations of hydrogen ions, you can think of pH as a measure of how concentrated the hydrogen ions are in a solution. The scale is “reversed,” though: the higher the concentration of hydrogen ions a solution has (the more acidic it is), the lower the pH value is. In this lab, you will use pH paper to determine the pH of several household solutions. Procedure Safety note: Never touch or taste any solution during a lab activity! As your complete each step of the procedure, put a checkmark ( ) in the box next to the appropriate step. 1. Obtain the necessary materials. Make sure you have all the necessary materials at your lab station: A well plate A pH color chart Tweezers Paper towels Several pieces of pH paper Take your well plate to the stock solutions table. Use separate droppers to place five drops of each different solution in different wells. Make sure you use a different dropper for each solution. In the diagram below, record which solution was placed in each well: Take your prepared well plate back to your lab station. 2. Determine the pH of each household solution. Using your tweezers, dip the corner of a small piece of pH paper into one of the solutions. Be sure not to get the tweezers wet! Observe its color before laying the pH paper on a paper towel. Use your pH color chart to estimate the pH of the solution to the nearest 0.5 pH. Record the solution name, pH paper color, and estimated pH in the data table below. Classify the solution as an acid, a base or neutral. Repeat the above steps for all of your household solutions. 3. Clean up your work area. Placed your used pH paper in a paper towel and throw away your paper towel. Rinse your well plate thoroughly with detergent at the sink. Shake off any excess water. Take your well plate back to your lab station and dry it thoroughly with clean paper towels. Organize your work area. Raise your hand to have your teacher check your lab station and dismiss you to your desk to work on the post-­‐lab questions. Results Table 1. pH Test results for different solutions Solution Name pH paper color Estimated pH Acid/ Base/ Neutral Post-­‐Lab Questions 1. Which of the solutions you tested were: a. acids? b. bases? c. neutral? 2. Do solutions derived from living things tend to be acidic or basic? 3. Write the names of each solution you tested on the pH table below. Place each solution name near its pH value. 4. Which of the solutions you tested… a. was the most acidic? b. was the most basic? c. had the highest concentration of hydrogen ions? d. had the lowest concentration of hydrogen ions? 8 neutral 5. Classify each of these common substances as acid, base, or neutral. a. Soap, pH 10.0: b. Stomach acid, pH 1.0: c. Sea water, pH 8.0: d. Distilled water, pH 7.0: e. Milk of magnesia, pH 10.7: f. Lemon juice, pH 2.5: g. Human blood, pH 7.4: h. Bleach, pH 11.0: i. Normal Rainwater, pH 5.6: 0 1 2 3 4 5 6 7 9 10 11 12 13 14