Colorimeter pH Lab

What is the difference in pH between an acid and a base?

The difference in pH between an acid and a base can range anywhere from 0 to 14. The pH of an acid is below 7, and the pH of a base is above 7. This shows a difference in the concentration of the hydrogen ions in a substance. pH is measured by -log[H+], so high hydrogen ion concentration results in a low pH due to the inverse relationship.

What is the relationship between pH & pOH?

pH and pOH are related because they add to fourteen. In other words, pKw= pH + pOH = 14.

How are pH & pOH related to [H+] & [OH-] respectively?

pH and pOH are inversely related to [H+] and [OH-], respectively. pH and pOH are calculated by taking the negative log of the ion concentration, or in other words, taking the inverse of the concentration. This means that a high concentration of ions will result in a low pH or pOH, and a low concentration of ions will result in a high pH or pOH.

What differences did you observe between Universal Indicator and the other indicators?

I observed that the Universal indicator could be used to determine the pH of almost any reaction, while the other indicators were limited in their usefulness. These indicators would be better suited to verify a pH, rather than determine a pH.

If you know a neutralization reaction will occur at a pH of 5 and a different neutralization reaction will occur around a pH of 9, would you choose the same indicator or different indicators? Why?

I would choose different indicators because different indicators would provide more specific results. pH indicators that are specifically targeted for these two pH’s will be more accurate than using the same indicator.

What are indicators?  How do they work?  Do they have limits? (Provide specific examples from your lab.)

An indicator is a chemical compound that changes color when exposed to certain conditions. The indicators interact with H+ and OH- in a system, and give off a certain color as a result of neutralization. Indicators have limits in terms of the range of pH’s that they can qualitatively demonstrate. Universal indicator has the ability to show the entire range of pH from pink to purple, but other specific indicators can only exhibit certain changes. For example, bromothymol blue can only show from yellow to blue.


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