It is important to measure the pH of the water, i.e. its acidity or alkalinity level. The water is absorbed by the plants and animals on which we depend and we drink it ourselves. This data provides us with various information and allows us to understand if the water is potentially contaminated. For this reason, measuring its pH is a fundamental precaution to ensure public health.
Steps
Method 1 of 3: Use a pH meter
Step 1. Calibrate the probe following the manufacturer's instructions
You need to do this by testing a substance with a known pH. This way you can adjust the tool accordingly. If you are about to measure the pH of the water outside the laboratory, you must proceed with the calibration several hours before taking the instrument to the test site.
Rinse the probe with clean water before using it. Dry it with a clean tissue
Step 2. Collect a water sample with a clean container
- The sample must be sufficient to cover the electrode tip.
- Let the water settle for a moment so the temperature can stabilize.
- Measure its temperature with a thermometer.
Step 3. Set the instrument according to the sample temperature
The sensitivity of the probe is influenced by the water temperature, so the results you get may not be accurate if you do not enter this information.
Step 4. Put the probe in the water
Wait for the meter to reach equilibrium, which occurs when the readings begin to be constant.
Step 5. Read the pH value detected by the device
The pH meter should give you a value between 0 and 14. If the water is pure, the figure should be close to 7. Write down your readings.
Method 2 of 3: Using Litmus Papers
Step 1. Distinguish an indicator from a litmus paper
To get an accurate reading of the pH of a solution, you should use an indicator, which is not to be confused with litmus paper. Both are used to test acids and bases, but have important differences.
- The pH indicator strips contain a series of bars that change color once they come into contact with the solution sample. The reaction that an acid or base triggers on the bars changes according to its strength. Once the indicator strip has changed color, you can compare it to the reference examples contained in the kit.
- Litmus paper is a strip of paper that contains an acid or base (alkaline). The most common are the red ones (which contain an acid that reacts with the bases) and the blue ones (which contain a base that reacts with acids). The red stripes turn blue if they come into contact with an alkaline substance, and the blue ones turn red if they touch an acid. Litmus papers are great for quickly and easily testing a substance, but cheaper papers don't always provide an accurate answer as to the strength of a solution.
Step 2. Collect a water sample in a clean container
It must be enough to completely cover the strip.
Step 3. Immerse the indicator paper in the water
It only takes a few seconds of contact. The various bars on the map will begin to change color in a few moments.
Step 4. Compare the end of the strip with the color table that is included in the kit package
The color (or colors) of the table should match the one (or ones) you can see on the strip. The table shows a legend with which you can trace the pH levels.
Method 3 of 3: Understanding the pH
Step 1. Learn the definition of acid and base
Acidity and alkalinity (the term used to describe the bases) are defined by the ability of a substance to lose or accept hydrogen ions. An acid is a substance that loses (in some way we can say that it “donates”) the hydrogen ions; a base is a substance that accepts extra hydrogen ions.
Step 2. Understand the pH scale
This is a value that is used to measure the alkalinity or acidity level of a water soluble substance. Water normally contains an equal number of hydroxide ions (OH-) and hydroxonium (H30 +). When an acidic or basic substance is dissolved in it, the ratio of hydroxides to hydroxones changes.
- The pH scale is usually defined in a range between 0 and 14 (although there are substances that go outside this range). Neutral substances have a pH close to 7, acidic ones below 7 and basic ones above 7.
- The pH scale is logarithmic, which means that each integer range equals a strength of alkalinity or acidity ten times higher or lower. For example, a substance with pH 2 is ten times more acidic than one with pH 3 and 100 times more acidic than one with pH 4. The same goes for bases.
Step 3. Know why it is important to test the pH of the water
The pure one should have a pH equal to 7, although the tap one is slightly acidic (pH between 6 and 5, 5). Very acidic water (with a low pH) is more able to dissolve toxic chemicals. These can contaminate the water and make it unsuitable for human consumption.
