When we look for answers in GlobalLab, we base our conclusions on data we all submit. But when we use probes and sensors, and since each of us uses our own instruments to collect data, how can we know whether our findings can be compared? How do we know our instruments even measure their target, in this case pH, or measure with comparable accuracy? What can be done so we can trust each other’s findings? For pH measurements scientists use a procedure called the calibration of pH probes. We check how accurately our probes and sensors measure pH by first measuring so-called ‘standard solutions,’ those with pH values we already know, since we either prepared them ourselves or purchased them from chemical catalogs.

What if you measure the pH of a chilled solution that you just removed from the refrigerator, and somewhere else, others measured the pH of the same solution but at room temperature on a warm day? Does the temperature of a solution affect its pH? If so, what does this mean for our investigations into pH? Should we measure pH when the solutions are at the same temperature?

Litmus, methyl orange, and phenolphthalein are well-known and broadly used acid-base indicators. But did you know that some plants can also be used as indicators?

Plants can sometimes reveal pH. This is because some plant can live only in soils with narrow and specific ranges of pH. We’ll explore whether we can tell the pH of the soil just by the plants that grow there.

Fresh milk right from the cow has a pH value that is almost neutral. Gradually, however, milk becomes sour, even when it is stored in a refrigerator. In this investigation we will see if we can tell how many days old the milk is simply by measuring its pH. We will also investigate the microorganisms at work in its change in acidity.

Sometimes people preserve fruits by adding water, sugar, and some spice to make a fruit preserve, and then putting the preserve in a tightly sealed jar. But when fruit preserves are stored in a warm place, they start fermenting, which is a chemical breakdown by microorganisms like bacteria, and they get sour. What does this process have in common with the souring of milk?

Every citrus fruit contains organic acids, such as citric acid and ascorbic acid, also known as vitamin C. Yet limes or lemons taste quite acidic while oranges or mandarins are on the sweet side. Which among citrus fruits is the "world champion" in acidity? Is there a correlation between acid taste and pH-levels? Are there variations in pH for the same citrus fruit grown in various countries, regions or climate zones. Those questions will be explored in this activity.

Berries differ by the amounts of sugar and organic acids, such as citric acid and ascorbic acid (vitamin C). Which type of berry is the most acidic? Is it true that the more sour a berry, the lower is its pH? Working together in this investigation, we will find out.

Animals are distributors of seeds. They eat fruits and expel seeds, enabling new plants to grow far from the mother plant. The sweeter and riper the fruit, the more attractive it is to animals. But are seeds ready for germination when their fruits are most ripe? Let’s find out, using apples.

What is acid rain? Where does it come from? Can acid rain affect the environment? In this investigation, we will monitor the pH of rain and snow, overlaid with wind speed and direction, to get a sense of where acid rain comes from.

Let’s check the acidity of the water in our river, pond or lake. Do pH levels change over the course of a day? Is there a relationship between acidity and eutrophication, when a body of water loses its oxygen and becomes a marsh?

To avoid problems with your teeth or your health in general, the pH of tap water you drink should be close to neutral. But what is the actual pH of the tap water you drink? Does the pH of tap water change over the course of the day? Does it change day by day? Or after a large rainfall or snowstorm?

Many people drink bottled water with and without carbonation. Let's compare the acidity of carbonated soda and water without carbonation. Let’s also see if the pH of soda changes if the bottle is left open for a long time.

What happens to unfinished soda? Many soft drinks are easy to tell apart by their tastes; they all are made from different recipes. But what they have in common is the presence of carbon dioxide. Compare the original acidity of soda with what happens to pH levels as the soda loses its carbonation and goes “flat”.

Soil is a complex ecosystem that is home to many organisms, which determine its fertility. The pH of soil affects the development of organisms that inhabit it and the solubility of minerals. Working together, we can map soil pH and, at the same time, find out if the color of the soil indicates its acidity.

Everyone can recall the dry mouth we experienced before a big exam or performance. Yet when we’re alone, especially before lunch, the saliva in our mouths is very different. We’ll compare the acidity of saliva before and after meals, when alone, and in stressful situations.