# pH and pH meter - Ohio University

pH pH is a unit of measure which describes the degree of acidity or alkalinity (basic) of a solution. It is measured on a scale of 0 to 14. The formal definition of pH is the negative logarithm of the hydrogen ion activity. pH = -log[H+] pH value

The pH value of a substance is directly related to the ratio of the hydrogen ion and hydroxyl ion concentrations. If the H+ concentration is higher than OHthe material is acidic. If the OH- concentration is higher than H+ the material is basic. 7 is neutral, < is acidic, >7 is basic The pH scale The pH scale corresponds to the

concentration of hydrogen ions. If you take the exponent of the H3O+ concentrations and remove the negative sign you have the pH of the solution. For example pure water H+ ion concentration is 1 x 10^-7 M, therefore the pH would then be 7. pH The addition of acid to water increases the

concentration of hydrogen ions and reduces the concentration of hydroxyl ions The addition of a base would increase the concentration of hydroxyl ions and decrease the concentration of hydrogen ions Acids and Bases An acid can be defined as a proton donor, a chemical that increases the

concentration of hydrogen ions in solution. A base can be defined as a proton acceptor, a chemical that reduces the concentration of hydrogen ions in solution. pH Measurement A pH measurement system consists of three parts: a pH measuring electrode, a reference electrode, and a high input meter.

The pH measuring electrode is a hydrogen ion sensitive glass bulb. The reference electrode output does not vary with the activity of the hydrogen ion. pH Meter A sample is placed in a cup and the glass probe at the end of the retractable arm is placed in it. The probe is connected to the main box.

There are two electrodes inside the probe that measure voltage. One is contained in liquid with fixed pH. The other measures the acidity of the sample through the amount of H+ ions. pH Meter A voltmeter in the probe measures the difference between the voltages of the two electrodes.

The meter then translates the voltage difference into pH and displays it on the screen. Before taking a pH measurement the meter must be calibrated using a solution of known pH. Temperature and Buffers Temperature compensation is contained within the instrument because pH electrodes are

temperature sensitive. Temperature compensation only corrects for the change in the output of the electrode, not for the change in the actual solution. Buffers are solutions that have constant pH values and the ability to resist changes in pH. They are used to calibrate the pH meter.

## Recently Viewed Presentations

• UPDATE IN PLACE:A Poison Apple? Jim Gray, 1981 "..for performance reasons, most disc-based systems have . been seduced into updating the data in place." 30 years of hardware i
• Portions of this presentation were created with Thyra Rauch. ... Validate understanding of tasks and context. Improved UX = more satisfied users. Less training needed. ... Avoid leading or giving clues. Encourage to elaborate. Probe don't demand.
• Used high-resolution, cloud-resolving model to simulate two different types of storm systems at a regional scale: warm summer thunderstorms in southeastern China and cool, windy frontal systems on the Great Plains of Oklahoma.
• Guidelines for Homework 6 Getting Started Homework 6 requires that you complete Homework 5. All of HW5 must run on the GridFarm. HW6 may run elsewhere (like your desktop).
• What is ACP saying about measures? Fill critical gaps in quality measurement. Obtain . stakeholder input . into the measure development process. Focus on outcomes-based measures, patient and family experience measures, care coordination measures, and measures of population health and...
• (See detailed procedures on pages 21-22 of the Trainer Manual.) (The next slide concludes the activity). Note to Trainer: You may want to ask anyone in ill-health to not participate due to the closeness of the final step of the...
• Lecture 15. Pattern Classification (I): Statistical Formulation
• Write an essay in which you explain how Paul Bogard builds an argument to persuade his audience that natural darkness should be preserved. In your essay, analyze how Bogard uses one or more of the features in the directions that...