P h meter use and calibration
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A pH meter measures the concentration of hydrogen ions (H+) in a solution using an ion-sensitive electrode. It has a glass electrode and reference electrode in one tube. When measuring pH, a salt bridge forms allowing sodium ions (Na+), not H+, to cross the glass membrane and allow the pH meter to measure the H+ concentration. To calibrate the pH meter, it is placed in high, neutral, and low pH buffer solutions. Litmus paper can also indicate pH but a pH meter provides a more precise measurement. The pH scale ranges from 0-14 with lower numbers indicating more acidity and higher numbers indicating more basicity.
P h meter use and calibration
- 1. pH Meter - Use and Calibration
- 2. What is a pH Meter? • An instrument that measures the H+ion concentration (pH) of a solution using an ion sensitive electrode which will ideally respond to one specific ion, in this case H+ • The pH of a solution is the negative logarithm of the H+ion concentration • A typical modern pH meter has a glass and reference electrode in one tube
- 3. How Does a pH Meter Measure H+ Concentration? The pH meter has two electrodes in one tube, glass and reference electrode. A saturated KCL and HCL solution is contained in a tube which is inside of an outer tube that will have contact with the solution to be measured. This outer tube has a double glass bulb with NA+which makes an ion specific electrode. When measuring the pH of a solution, a salt bridge forms. The NA+ion, not H+, crosses the glass membrane of the pH electrode and allows for a change in free energy which is measured by the pH meter as the concentration of H+.
- 4. Calibrating a pH Meter • Make sure the meter is in pH mode • For a 3 point calibration, use high pH (--), pH 7.0 and low (-.0) solution • Before calibration, rinse probe thoroughly with de-ionized water or a rinse solution • Immerse the end of the probe completely in the calibration solution • Stir the probe gently to create a homogenous sample
- 5. Measuring the pH of a Solution • Always rinse electrodes with de-ionized water prior to placing in a solution for pH measurement • Allow meter to stabilize for 30 seconds or a minute, then read • Remove electrodes and rinse with de-ionized solution • The pH bulb should always be stored wet preferably in pH 4.0 buffer with 1/100 KCl • Other buffers or tap water can be used for storage
- 6. Maintenance of pH Meter • Wipe off exterior of pH meter with a damp cloth after use • The outside of the meter is made of polyester and is not affected by most solvents but is affected by some organic solvents • pH the “power of hydrogen”
- 7. Litmus Paper A Quick Method for Determining pH
- 8. Litmus Paper • Litmus paper is useful to determine the pH of a solution when you do not have a pH meter available • Proper storage of the litmus paper is essential to maintain quality control
- 9. The pH Scale • The pH measures the concentration of H+in a solution • The lower the number, the more acidic the solution • The higher the number, the more basic the solution
- 10. The pH Scale – Another Description