An acid is a substance that releases hydrogen ion (H) when it disassociates and therefore increases the hydrogen ion concentration of a water solution. A base is a substance that accepts hydrogen ions and therefore decrease the H+ concentration of a solution. Hydroxide ions (OH) readily accept hydrogen ions. Because substance have a different concentration of hydrogen ion (H*) the pH scale was devised to measure these differences. The pH scale ranges from 1 to 14. A neutral substance has an equal number of hydrogen ions (H*) and hydroxide ions (OH) and is therefore neither acidic nor basic. All neutral substances have a pH of 7. Any substance with a pH from just below 7 to 1 are considered acidic. The stronger the acidity, the lower the pH number. Any substances with a measured pH from above 7 to 14 are considered basis (alkaline). The stronger the base, the higher the pH number. Procedure 1.Your instructor will place a sample of each substance to be tested at every table. You must share these samples with the other groups at your table. 2. Dip either the Red/Blue Litmus Paper, the Hydrion Paper, or the pH Meter into the appropriate solution. Note red litmus paper will turn blue if a compound is basic, and blue litmus paper will turn red if the compound is acidic. If the red or blue litmus paper does not change color the pH of the substance is neutral. 3. Make sure you use a new piece of Litmus Paper and Hydrion Paper for each solution. 4. Make sure you rinse off your pH Meter with water after recording the pH for every solution. 5. When you are finish with the lab, make sure all the solutions are back in their original location on the table and securely closed. Throw all used Litmus Paper and Hydrion Paper in the garbage. Rinse of the pH Meter and turn it off. 9. In this lab, you used several methods to test the pH of solutions. Which of these methods was most precise? Explain. 10. Which of the pH methods was most subjective? Explain. 11. How is the accuracy of the pH meter assured?