Set

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Acid

An acid (from the Latin acidus/acēre meaning sour) is a chemical substance whose aqueous solutions are characterized by a sour taste, the ability to turn blue litmus red, and the ability to react with bases and certain metals (like calcium) to form salts. An aqueous solution of an acid has a pH of less than 7 and is colloquially also referred to as 'acid' (as in 'dissolved in acid'), while the strict definition refers only to the solute. An acid usually contains a hydrogen atom bonded to a chemical structure that is still energetically favorable after loss of H⁺ (a positive hydrogen ion or proton). A lower pH means a higher acidity, and thus a higher concentration of positive hydrogen ions in the solution. Chemicals or substances having the property of an acid are said to be acidic.

There are three common definitions for acids: the Arrhenius definition, the Brønsted-Lowry definition, and the Lewis definition. The Arrhenius definition defines acids as substances which increase the concentration of hydrogen ions (H⁺), or more accurately, hydronium ions (H₃O⁺), when dissolved in water. The Brønsted-Lowry definition is an expansion to include solvents other than water: an acid is a substance which can act as a proton donor. By this definition, any compound which can be deprotonated can be considered an acid. Examples include alcohols and amines which contain O-H or N-H fragments. A Lewis acid is a substance that can accept a pair of electrons to form a covalent bond. Examples of Lewis acids include all metal cations, and electron-deficient molecules such as boron trifluoride and aluminium trichloride.

Arabs

Arabs (/ˈærəbz/; Arabic: عرب‎, ‘arab) are a major panethnic group whose native language is Arabic, comprising the majority of the Arab world. They primarily inhabit Western Asia, North Africa, and parts of the Horn of Africa. Before the spread of Islam, Arab referred to any of the largely nomadic Semitic tribes inhabiting the northern and central Arabian Peninsula. In modern usage Arab refers to a heterogeneous collection of Arabic-speaking peoples in the Middle East and North Africa. The ties that bind Arabs are linguistic, cultural, and political, and to a lesser extent genetic, with Arabized Arabs displaying genetic admixture from the Arabian peninsula as well as indigenous elements. As such, Arab identity is based on one or more of genealogical, linguistic or cultural grounds, although with competing identities often taking a more prominent role, based on considerations including regional, national, clan, kin, sect, and tribe affiliations and relationships. Not all people who could be considered Arab identify as such. If the Arab panethnicity is regarded as a single population, then it constitutes the world's second largest group of people after the Han Chinese.

Com

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