State Standard H.1L.4 -- Explain how cellular processes and cellular differentiation are regulated both internally and externally in response to the environments in which they exist. / First Name / Last Name
Response / Scoring Rubric 1-4 / Score
10 / Excellent / Responses are clear, complete and demonstrate a thorough understanding of the subject matter
8 / Meets / Completes the assignment or experiment satisfactorily, but the explanations have minor flaws
6 / Nearly Meets / Begins the assignment and explanation satisfactorily; but omits significant parts or fails to complete.
4 / Does Not Meet / Assignment and its explanations are not accurate. Group did not demonstrate understanding or authentic knowledge
1 / Fails to complete / Did not participate
Measuring pH
Inquiry: How can you determine if a substance is an acid or a base?
Introduction: The chemistry of a substance makes the substance either and acid or a base. Acids are compounds that are chemically bound with hydrogen (H). The hydrochloric acid (HCI) in your stomach is an example of an acid. Bases are compounds that contain a combination of oxygen and hydrogen called a hydroxyl (-OH). Ammonia is an example of a strong base. An acid has the ability to donate its Hydrogen ion (H+). A base has the ability to accept this proton.
The pH scale is used to determine the acidity or alkalinity (how basic it is) of a substance. An indicator changes color when an acid or a base is present. It “indicates” if the substance tested is an acid or a base. In this lab, you will use an test paper to create a simple pH scale. What chemical properties do you think enable it to be used as an indicator? At neutral pH, the scale is 7 indicating water.
Objectives: -PREPARE a pH indicator.
-OBSERVE indicator color changes at various pH’s.
-CLASSIFY substances as either acids or bases.
Prelab Activities
Concepts: Review sections in your notes that describes the properties of acids and bases. Consider which food substances that you are familiar with might be acids or bases. Weak acids in foods tend to be sour-tasting. Bases, on the other hand, often taste bitter.
Acids and bases can be arranged on a pH scale according to their strengths. The pH scale runs from 0 to 14. Acidic substances fall in the 0.1 to 6.9 part of the scale. The lower the number, the stronger the acid. Basic substances fall in the 7.1 to 14 part of the scale. The higher the number, the stronger the base. Water, which is neutral (neither acid nor base) has the number 7.0 at the center of the pH scale. An approximate pH-scale number may be assigned to substances you test based on the degree of color change in each substances causes in the indicator as compared to other substances.
Materials (per pair)
Dropper, Water, small plastic cups, pH paper, Substances for testing: lemon juice, vinegar, milk of magnesia, milk, water, a raw egg white, banana, ammonia, baking soda solution.
Procedure (Wear gloves and goggles)
1. Work with a partner. Wear your safety goggles.
2. Take 10 testing strips and make your way around the room testing the pH of the various substances at the lab stations.
3. Use the pH scale to determine pH.
4. Record pH in the data table 1.
Data Record
Table 1
SubstancepH
Table 2
Acid / pH / Base / pH
Analysis
1. Rank the acids from strongest to weakest according to pH in table 2.
2. Rank the bases from strongest to weakest according to pH in table 2.
3. Explain how water is used as the basis for the pH scale.
4. Lye has the chemical formula NaOH. Deduce what kind of substance you would use to neutralize lye.