Serial Activity Class Copy

In this activity you will perform serial dilutions on both acid and base . This will give you experience with the technique, serve as calculation review as well as introduce you to acids, bases and indicators! Serial dilution is the stepwise dilution of a solution. It results in a very precise and very dilute solution. Generally, each step of the dilution is kept as constant factor, often 10-fold.

This process has many applications in chemistry, but is often used in labs. A microbiologist might prepare a serial dilution of a bacterial colony so as to be able to count a reasonable amount of cells and calculate back to the initial in the sample.

Goal: Correctly calculate and prepare serial dilutions on 1.0 M HCl and 1.0 M NaOH solutions to create a pH indicator RAINBOW! Safety: ● Wear goggles ● Notify instructor of any spills or breakages ● Always add acid to water

Prelab: On student working copy.

Materials: Pipettes, small beaker, well plate, indicator Directions: Part 1: Perform a series of dilutions on 1.0 M HCl solution.

1. You will use 12 wells on the tray. Be sure to keep track of where you make each solution on the map that has been started for you. 2. Obtain a small bottle of 1.0 M HCl from the chemical supply station, a handful of pipettes and a well plate. 3. Obtain a beaker containing distilled water and a pipette - save whatever you do not use for the next class. 4. Place 10 drops of 1.0 M HCl into the first well. Close the bottle and return it to the chemical station. 5. NOTE: Use a clean pipette every time you obtain a drop of acid solution! (It seems a little wasteful but the solutions can be easily contaminated.) 6. Into the second well, make a ten-fold dilution by mixing one drop of 1.0M into 9 drops of distilled water. Record the concentration of the resulting solution on your map. Use your acid pipette to gently stir the solution, then place it aside on a paper towel as waste. Save your water pipette to use for the entire procedure. 7. Into the third well, make a ten-fold dilution by mixing one drop of the solution from well #2 into 9 drops of distilled water. Record the concentration of the resulting solution on you map. 8. Repeat this process for a total of 6 wells. (this includes your initial 1.0M solution, you should have 6 wells with solution at this point) 9. Throw away all of your HCl pipettes.

Part 2: Perform a serial dilution on 1.0 M NaOH solution.

Repeat steps 1-8 replacing the HCl with NaOH.

Part 3: The rainbow.

1. When you are done with your dilutions and have recorded the correct on your map call over your instructor. 2. Test your serial dilutions for the chemistry rainbow!

Part 4: Neutralization Neutralization is the process where an acid and a base react to produce neutral water and an ionic salt.

HCl (aq) + NaOH (aq) → H2O (l) + NaCl (aq)

+ - The net ionic equation looks like this: H (aq) + OH (aq) → H2O (l)

For this section, follow the steps provided within the questions on your working student copy.

CLEAN UP: 1. Return all supplies to chemical supply station. 2. Carefully pour the contents of the well plate down the drain. 3. Wash well with soap and water. 4. Dry completely and return well plate to supply station. 5. Wash your hands.

Serial Dilution Activity Name ______

In this activity you will perform serial dilutions on both acid and base solutions. This will give you experience with the technique, serve as solution calculation review as well as introduce you to acids, bases and indicators! Serial dilution is the stepwise dilution of a solution. It results in a very precise and very dilute solution. Generally, each step of the dilution is kept as constant factor, often 10-fold.

This process has many applications in chemistry, but is often used in microbiology labs. A microbiologist might prepare a serial dilution of a bacterial colony so as to be able to count a reasonable amount of cells and calculate back to the initial concentration in the sample.

Prelab: 1. Karissa obtains a 1.0 M solution of hydrochloric acid. She performs a 10-fold dilution by adding 1.0 mL of this solution to 9.0 mL of distilled water. What is the concentration of the resulting solution?

2. She performs another 10-fold dilution on the solution produced in question #1. What is the concentration of the resulting solution? Also, how much of the solution from question #1 is left over?

MAP: Part 1 and 2:

Well #1 1.0 M HCl

Part 3:

1. Write the symbol for a hydronium ion ______, hydrogen ion ______and hydroxide ion ______

2. pH is a mathematical representation of the hydrogen ion concentration. What do you think is happening to the pH as you perform serial dilutions in Part 1? In Part 2?

3. Calculate the pH for each of the wells on your map above.

Part 4: Neutralization. 1. Predict what will happen, at a micro and macro level, if you mix the entire contents of your first HCl well that contains 9 drops of 1.0 M HCl with HALF of the contents of your first NaOH well that contains 9 drops of 1.0 M NaOH PREDICT: Micro Macro

2. Now, mix the entire contents of your first HCl well with half (about 4 drops) of the first NaOH well. Record your observations:

Is the solution neutralized? What is the approximate pH? ______, ______

3. Now, mix in the NaOH drops remaining in the first NaOH well into your HCl/NaOH mix. Record your observations:

Is the solution neutralized? What is the approximate pH? ______, ______

4. We can use stoichiometry to determine how much acid or base we will need to neutralize a solution. a. How many milliliters of 0.450 M HCl are required to neutralize 12 mL of 0.233 M NaOH?

b. How many liters of 1.78 M NaOH are required to neutralize 2.4 L of 1.00 M HCl?