Chemistry+Method

=Variable=

//Independent// – sample of swimming pool water from three different locations //Dependent// – pH values, number of drops of acid or base before the pH values get out of the buffer region //Controlled// – concentration of acid/ base, volume of swimming pool water, amount of acid/ base in each drop The //controlled group// is the buffer capacity of distilled water.

=Materials=


 * pH probe
 * laptop
 * Logger Pro software
 * at least three 50 ml beakers
 * goggles
 * apron
 * pipette
 * 50 ml distilled water
 * 50 ml 0.1 M of NaOH(aq)
 * 50 ml 0.1 M of HCl(aq)
 * three swimming pool water samples



Figure 1: 50 ml of distilled water, Sodium Hydroxide solution of 0.1 M, and Hydrochloric acid solution of 0.1 M

= = Figure 2: Three samples of swimming pool water from three different locations

=Procedure=

1. Set up the pH probe. Connect the pH probe to the Vernier logger pro interface at channel 1, then connect the interface to the laptop and open the software program of Logger Pro. The data collection table should appear as the number of drops for the independent variable (x-axis) and pH for the dependent variable (y-axis). Set the mode to “Events with entry” from the “clock” icon.

Figure 3: Setting up pH probe

2. Insert the pH sensor to the sample of the swimming pool water. Click “collect”, wait until the pH value stabilizes, click “keep”, and indicate that as drop 0. That’s the initial pH of the swimming pool water sample. ==

Figure 4: inserting pH sensor to the sample of swimming pool water

3. Add one drop of the strong base NaOH and wait till the pH value stabilizes, and then click “keep”. Indicate that as drop 1. ==

Figure 5: Dropping NaOH solution to the sample of swimming pool water

= = 4. Add the second drop of NaOH, wait till pH value stabilizes, click “keep”, and indicate that as drop 2. Keep doing it until the tenth drop. 5. Repeat step 2 and 3 for the other two samples, but before that, wash the pH sensor using distilled water. Make sure the sensor part is rinsed well. 6. Now repeat the same method by using the strong acid HCl to all samples. 7. To get the data for the controlled group, repeat the same method of adding NaOH and HCl to the distilled water.