Chemistry Homework

Lab 8: Chemical Reactions I

Pre-lab Questions

1. Name the chemical that makes up teeth.

1. How does plaque harm teeth?

1. How does fluoride promote dental health?

1. Write two solubility rules that are used in this lab.

Experiment: Battle of the Mouth Rinses

Some mouth rinses contain fluoride, usually in the form of sodium fluoride, which is soluble in water. In this lab, you will determine which one of two mouth rinses would be better at preventing cavities by replacing lost minerals with fluoride. You will do this by determining which rinse contains fluoride.

Procedure

**Take photographs of your experiment set up and your results. Submit them with your laboratory report.**

1. Label the two test tubes with a permanent marker as A and B.

HINT: Make sure to write down which rinse is A and which is B.

1. Pour 10 mL of Rinse A into the test tube marked A.

2. Pour 10 mL of Rinse B into the test tube marked B.

HINT: If using the same graduated cylinder to measure your rinses, wash the cylinders WELL between pours to prevent cross-contamination.

1. Pour 3 mL of 1 M Ca(C2H3O2)2 solution into each of the test tubes. Gently stir each test tube with a stir rod to mix. Be sure to clean your stir rod each time before placing it in a solution.

CAUTION: Mixing should be done gently to prevent glass breakage and injury.

1. Observe and record initial observations immediately after adding calcium acetate to the test tubes.

2. Observe the reactions for at least 10 minutes to ensure it is finished. HINT: A positive test is indicated by a cloudy appearance of the solution. The precipitate formed can be more easily seen if the test tube is held up to the light. The precipitate will eventually settle to the bottom of the test tube.

3. Let the test tubes sit for an hour. After an hour, record final observations.

4. Record all observations in the Data section.

5. To clean up, you can rinse the small amount of precipitate down the drain.

Data

• Observations of NaF and Ca(C2H3O2)2 (see sequence of pictures below)

• Observations of Rinse A and Ca(C2H3O2)2

• Observations of Rinse B and Ca(C2H3O2)2

Post-lab Questions

1. Take photographs of your experiment set up and your results. Submit them with your laboratory report.

1. Did either of the mouth rinses contain fluoride? How did you know?

1. Which mouth rinse would be better at fighting cavities? Why?

1. Based on the solubility rules learned in this lab, could you use potassium nitrate to test for fluoride in mouth rinses? Explain your answer.

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