What makes something acidic or basic? It all comes down to hydrogen. When we measure the acidity of alkalinity, we use the pH scale, which literally stands for the "potential of hydrogen." When we dissolve acids in water, we create excess hydrogen ions that are positively charged (H+). These hydrogen ions bind to water (H2O) to create hydronium (H3O+). The more hydronium present in the solution, the more acidic it is.

Conversely, when we dissolve bases in water, we create excess negatively charged hydroxyls (OH-). The more hydroxyls present in the solution, the more basic it is. Pure water has the exact same amount of hydronium as hydroxyls, making it neutral on the pH scale.

The pH scale can be considered a positive and negative integer number line. On the number line, zero is the "middle" of the number line, and negative and positive numbers emanate from it. The farther away from zero, the more positive or negative the number is. This is similar to how we use the pH scale. A significant difference is that we use the pH value of seven instead of zero as the neutral number. The scale goes from one to fourteen. Any number less than seven is acidic; any more than seven is basic. The further away from seven on the pH scale, the "stronger" and more reactive it is. The scale is also logarithmic, so a solution with a pH of four is ten times more acidic than pH five and a hundred times more acidic than a pH of six.

When I played volleyball, the scoring system was not what it is today. Nowadays, rally scoring is used, which means that the serving and receiving team can score on every play. The old scoring method used when I played was "side out," which meant only the serving team could score. If the receiving team won the rally, they did not receive a point but earned the right to

serve. While rally scoring dramatically sped up the game and made it more exciting, it meant a bad serve was a point for the other team. I have seen plenty of games lost on a missed serve, which is heartbreaking. In the side-out version, a bad serve only gives the serve to the other team and does not result in a point.

In Acid and Bases Volleyball, one team will be acid, and one will be base. They will play volleyball with the intent of getting their score to either one or fourteen. The score starts at seven since that is neutral. As they play, they make the solution more acidic or basic as they win and lose points to each other. With a small change, we can harness all the fun of volleyball to demonstrate how pH scales work!

Materials:

• A large play area

• A volleyball net

• One red volleyball and one blue volleyball

• A whiteboard to keep score of the game

• Dry Erase markers

  o Preferably one black, blue, and red

• Optional

  o Red jerseys o Blue jerseys

• Minimum Number of Students Needed:

  While you could play this game with as few as two people, it is more fun with an entire class.

Prior Knowledge: This lesson could be used to introduce acids and bases to your class or serve as a review of the pH scale.

Age: Upper elementary and middle school