Diseases, Conditions, Syndromes

Parasite needs chemical (lipid/nutrient) in cat intestines for sex

Toxoplasma gondii is a microbial parasite that infect humans and complete its full life cycle only in cats. New research published August 20 in the open-access journal PLOS Biology shows why: the sexual phase of the parasite's ...

Medical research

Scientists discover why brown fat is good for people's health

Rutgers and other scientists have discovered how brown fat, also known as brown adipose tissue, may help protect against obesity and diabetes. Their study in the journal Nature adds to our knowledge about the role of brown ...

Diseases, Conditions, Syndromes

Gut microbiome composition could make diarrhea less likely

Antibiotics are known to upset the balance of bacteria in the intestinal tract. In some cases, antibiotics can cause the bacterium Clostridium difficile (C. difficile) to overgrow wildly, causing diarrhea and, in severe cases, ...

Health

Quinn on Nutrition: Incomplete proteins

Q: Thanks for your very informative column on the nutritional value of beans. One of the things you said was that beans are high in protein. Many years ago I read that beans were an incomplete protein, so you should eat them ...

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Acid

An acid (from the Latin acidus/acēre meaning sour) is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red. Chemicals or substances having the property of an acid are said to be acidic.

Common examples of acids include acetic acid (in vinegar), sulfuric acid (used in car batteries), and tartaric acid (used in baking). As these three examples show, acids can be solutions, liquids, or solids. Gases such as hydrogen chloride can be acids as well. Strong acids and some concentrated weak acids are corrosive, but there are exceptions such as carboranes and boric acid.

There are three common definitions for acids: the Arrhenius definition, the Brønsted-Lowry definition, and the Lewis definition. The Arrhenius definition states that acids are substances which increase the concentration of hydronium ions (H3O+) in solution. The Brønsted-Lowry definition is an expansion: an acid is a substance which can act as a proton donor. Most acids encountered in everyday life are aqueous solutions, or can be dissolved in water, and these two definitions are most relevant. The reason why pHs of acids are less than 7 is that the concentration of hydronium ions is greater than 10−7 moles per liter. Since pH is defined as the negative logarithm of the concentration of hydronium ions, acids thus have pHs of less than 7. By the Brønsted-Lowry definition, any compound which can easily be deprotonated can be considered an acid. Examples include alcohols and amines which contain O-H or N-H fragments.

In chemistry, the Lewis definition of acidity is frequently encountered. Lewis acids are electron-pair acceptors. Examples of Lewis acids include all metal cations, and electron-deficient molecules such as boron trifluoride and aluminium trichloride. Hydronium ions are acids according to all three definitions. Interestingly, although alcohols and amines can be Brønsted-Lowry acids as mentioned above, they can also function as Lewis bases due to the lone pairs of electrons on their oxygen and nitrogen atoms.

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