Posted: September 10th, 2022

 Measure and understand pH of different solutions

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I hope you can around 3-5 hours after to send me the questions. Because these Questions every easy. Maybe just few minutes you can finish these e Questions.
Objectives:
pH lab
 Measure and understand pH of different solutions
 Understand the importance of pH to living systems
Introduction:
Polar molecules that dissolve in water can form solutions that are acidic, neutral, or basic. Acids are
compounds that contain hydrogen and can dissolve in water to release hydrogen ions (H+) into solution. Some
simulations use H+ and some H3O+ (they are same thing for our purposes, chemistry, what
are you going to do?) For example, hydrochloric acid (HCl) dissolves in water as two ions:
HClinH2O H++Cl-
Bases are substances that dissolve in water to release more hydroxide ions (OH-) into solution. For example, a
common base is sodium hydroxide (NaOH) ie drain cleaner:
NaOH in H2O Na+ + OH-
The amount of acid (H+) ions in a solution is measured using the pH scale. The pH scale reads from 0 to 14.
The value 7 is given to neutral solutions, which have equal amounts of acid (H+) and base (OH-). The values
below 7 are acid (more and more H+) and the values above 7 (less and less H+) are basic. Both strong acids (i.e.
pH 1) and strong bases (i.e. pH 14) can burn skin, but weaker acids (i.e. pH 5) and weaker bases (i.e. pH 8) are
used in foods and common chemicals.
Living organisms can only survive within very small ranges of pH values near neutral. To keep the pH levels
within the living range, organisms regulate their pH by using buffers. Buffers are solutions that resist or prevent
Name ________________________
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changes in pH. Therefore, a buffer can keep a constant pH while different acids or bases are added to it. In the
human body, the blood has a buffer system to maintain pH levels in homeostasis near 7.4.
Go to the Phet pH lab:
https://phet.colorado.edu/en/simulation/ph-scale
Click on the simulation, then click on “Macro.”
To start, click on the black triangle that is next to the word, water.
Then choose drain cleaner. Then, to test the pH of the drain cleaner, click and drag the green circle that is
attached to the pH scale and put it into the solution of drain cleaner. The pH should read 13.0. Next, check the
pH of the solutions and fill in the table below.
Complete the chart by writing down the pH of the solutions that you test in this lab:
Solution
pH
Is it Acid/Neutral/Base?
Hand soap
Blood
Milk
Coffee
Orange Juice
Soda pop
Battery acid
1. Put drain cleaner back in the container. Then, add water to it by clicking on the blue knob next to
the water faucet. What happens as you add water to the drain cleaner?
2. Why does the pH change?
Now, go back to the main screen and click on “Micro.”
pH is a measure of hydrogen ions (H+) and hydroxyl ions (OH-). In this simulation, H+ is sometimes
written as a hydronium ion (H3O+); this is an H+ ion combined with a water molecule. When H30+ ions
are present, the pH of the solution is more acidic (a lower number), and when OH- ions are present,
the pH is basic and a higher number.
For these next 3 questions, answer whether there are more H3O+ (ie H+), OH- ions, or are they equal.
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3. Click and drag the green circle into water.
a) What happens to the ions? (more H3O+, more OH-, or are they equal?
b) What happens to the ions in drain cleaner?
c) What happens to the ions in vomit?
4. According to what we have learned in this simulation, why is water neutral?
5. What is the chemical definition of an acid?
6. What is the chemical definition of a base?
7. Why do you care about pH – how is it important to living organisms.
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