What makes acids acidic

Anything with a pH above 7 is basic. One of the earliest tests to determine acids from bases was the litmus test. A chemical patch turned red for acids, blue for bases. Today chemists can also use pH indicator paper, which turns every color of the rainbow to indicate how strong or weak an acid or base is.

By Lida Tunesi November 13, at am. A hydrogen atom consists of a proton positively charged particle , around which an electron negatively charged particle orbits.

To gauge whether something is an acid or base, and how strong it is, chemists employ the pH scale. The strongest acids are at the lowest end of the scale. The strongest bases sit at the highest end. Examples are often organic compounds, which while they have many hydrogens in their chemical structure, very few of these can break away in solution.

Acetic acid HC 2 H 3 O 2 is a weak acid, as only the hydrogen at the front of the equation that can dissociate, and it is not hugely energetically favourable for it to do so. The pH scale, with a list of substances at each pH. Acids at the top, bases at the bottom. Image credit below. I do like the fact that "pH" has an actual chemical and mathematical meaning, rather than just being a random set of letters.

The views expressed are those of the author s and are not necessarily those of Scientific American. A biochemist with a love of microbiology, the Lab Rat enjoys exploring, reading about and writing about bacteria. Having finally managed to tear herself away from university, she now works for a small company in Cambridge where she turns data into manageable words and awesome graphs. Follow S. Gould on Twitter. Already a subscriber?

The following equation is a good place to start:. We begin with two water molecules, and move some hydrogen atoms around. One water molecule gains a hydrogen and therefore takes on a positive charge, while the other water molecule loses a hydrogen atom and therefore becomes negatively charged. OH - is called a hydroxyl ion and it makes things basic. However, in water, there is a balance between hydroniums and hydroxyls so they cancel each others' charges. Pure water is neither acidic or basic; it is neutral.

So how does something become acidic or basic? That happens when the hydroniums and the hydroxyls are out of balance. If there are more positively charged hydroniums than negatively charged hydroxyls, then the substance is acidic. If there are more negatively charged hydroxyls than positively charged hydroniums, then the substance becomes basic. Watch out for that, and ask for clarification! Moreover, the hydrogen ion and hydroxide ion concentrations in everyday solutions can vary over that entire range.

In order to deal with these large numbers more easily, scientists use a logarithmic scale, the pH scale. Each one-unit change in the pH scale corresponds to a ten-fold change in hydrogen ion concentration. The pH scale is theoretically open-ended but most pH values are in the range from 0 to It's a lot easier to use a logarithmic scale instead of always having to write down all those zeros! By the way, notice how one hundred million million is a one with fourteen zeros after it?

It is not coincidence, it is logarithms! What the equation means is just what we said before: for each 1-unit change in pH, the hydrogen ion concentration changes ten-fold.

Pure water has a neutral pH of 7. The pH of a liquid or solution is often an important piece of information in science. Measuring pH can be done simply and quickly using pH test paper , pH indicator sticks , or a pH meter. To measure pH, a piece of pH test paper or an indicator stick is dipped into the liquid. Each color on the key represents a different pH. An example of a used pH indicator stick and the corresponding color key is shown below in Figure 1. They consist of a probe that is dipped in a solution, and a digital readout.

Table 2 below discusses what types of pH measuring devices are best for different science project applications, and offers a quick link to purchasing different pH test papers and indicator sticks.