Study finds iron may not improve fertility

A new study led by Boston University School of Public Health (BUSPH) researchers finds that there is no consistent association between consuming iron and becoming pregnant. The study, published in The Journal of Nutrition, ...

Oncology & Cancer

Scientists remind immune cells whose side they should be on

International group of scientists in the joint study of the laboratory of the Wistar Institute, University of Pittsburgh, and I.M. Sechenov First Moscow State Medical University discovered the change in activity of one of ...

Obstetrics & gynaecology

Healthy babies start with healthy moms

Athletes invest hours practicing before a big game. Runners train for months leading up to a marathon. A mother-to-be should likewise prepare herself for the mental and physical rigor of pregnancy, labor and caring for a ...


Getting your nutrients: From the source or supplements?

(HealthDay)—Americans are making shifts in the supplements they take—fewer multivitamins and vitamins C and E, more fish oil and vitamin D. Many think of supplements as magic bullets, but studies don't always support ...

Medical research

Stopping Parkinson's disease before it starts

An Osaka University-led research team has recently published findings that provide a ray of hope for the millions of Parkinson's disease (PD) sufferers worldwide. Although more common in those aged over sixty, PD can strike ...

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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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