How do indicators measure ph

Litmus Litmus indicator solution turns red in acidic solutions, blue in alkaline solutions, and purple in neutral solutions. Acids turn blue litmus paper red. Alkalis turn red litmus paper blue. Stays red. Turns red. Stays blue. On these ranges, phenolphthalein goes from colorless to pink, methyl red goes from red to yellow, and bromothymol blue goes from yellow to blue. For universal indicators, however, the pH range is much broader and the number of color changes is much greater.

See figures 1 and 2 in the introduction for visual representations. Usually, universal pH indicators are in the paper strip form. Additionally, pH indicators can be found in nature, so therefore their presence in plants and flowers can indicate the pH of the soil from which they grow. Nature contains several natural pH indicators as well: for example, some flower petals especially Roses and Hydrangeas , certain fruits cherries, strawberries and leaves can change color if the pH of the soil changes.

See figure 7. Refer to the table of Universal Indicator Color change figure 1 in the introduction for clarification. The household detergent contained a concentrated solution of sodium bicarbonate, commonly known as baking soda. As shown, the pH paper turns a dark blue: baking soda in solution is basic. Here is a closer look of the pH papers before and after dipping them in the lemon juice and cleaning detergent Figure 10 :.

Here is a simple demonstration that you could try in the lab or at home to get a better sense of how indicator paper works. Make sure to always wear safety glasses and gloves when performing an experiment! She finds 5 brands that she really likes, but since she never took any introductory chemistry classes, she is unsure about which one to purchase.

The first has a pH of 3. Which one should she buy? Answer: The brand that has a pH of 6. You decide to test the pH of your brand new swimming pool on your own. The instruction manual advises to keep it between 7. Shockingly, you realize it's set at 8. Click to enlarge Most of us, chemists or otherwise, have probably come across pH indicators at one point or another. You might not be aware of the large range of different indicators that can be used to identify varying pHs, however, or the reasons behind the colour changes observed.

Firstly, it might seem a little odd that different indicators are even required, considering that universal indicator gives us a broad range of colours across the pH scale. However, universal indicator gives us a range of gradual colour changes, across a range of pH, rather than clearer ones at more specific pH ranges. In these cases, we need to use an indicator that changes colour at a pH very close to the equivalence point — and this is where our different indicators come in.

This makes them useful for different reactions between acids and bases, which have different equivalence points; these are usually carried out as titrations , so the exact amount of one reactant added to the other can be monitored. For example, phenolphthalein has a range of 8. Methyl orange has a range of 3. So, different equivalence points explain why we require more than one type of indicator solution — why, then, do we observe these colour changes in the first place?

In a simplistic sense, it measures how acidic or alkaline a substance is — however, what the pH scale actually is is a logarithmic scale for measuring the concentration of hydrogen ions in a solution.