Acidic

For alternative meanings see acid (disambiguation).

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Acids and Bases:

Acid-base reaction theories

pH

Self-ionization of water

Buffers

Systematic_naming

Redox reactions

Electrochemistry

Strong acids

Weak acids

Weak bases

Strong bases

An acid (represented by the generic formula AH) is typically a water-soluble, sour-tasting chemical compound. An acid always has a pH of less than 7. It is a molecule or ion that contains hydrogen or that is able to give up a proton to a base, or accept an unshared pair of electrons from a base. An acid reacts with a base in a neutralization reaction to form a salt.

Chemical Characteristics

In water, there is the following reaction:

<math>\mbox{AH} +\mbox{H}_2\mbox{O} \leftrightarrow \mbox{A}^- + \mbox{H}_3\mbox{O}^+<math>

There is a distinction between weak acids and strong acids. For a strong acid, no AH remains in solution:

<math>\mbox{AH} +\mbox{H}_2\mbox{O} \rightarrow \mbox{A}^- + \mbox{H}_3\mbox{O}^+<math>

That is why the acidity constant is only defined for weak acids:

<math>Ka = {[A^-]\cdot[\mbox{H}_3\mbox{O}^+] \over [AH]}<math>

Some of the stronger acids include the hydrohalic acids - HCl, HBr, and HI - and the oxyacids, which tend to contain central atoms in high oxidation states surrounded by oxygen - including HNO₃, H₂SO₄, HClO₄.

Acidic (chemistry), the opposite to basic, reacting with basics to form salts. Acidic (geology), of rock: containing more than 65% of silica.

Characteristics

Acids are generally:

• Taste: sour when dissolved in water
• Touch: strong acids have a stinging feeling
• Reactivity: acids react violently with many metals
• Electrical Conductivity: acids are electrolytes

Acids in Food

• acetic acid or ethanoic acid: found in vinegar and tomato sauce
• ascorbic acid(vitamin C): found in fruits
• citric acid: found in citrus fruits
• carbonic acid: found in carbonated beverages
• lactic acid: found in dairy products such as yoghurt and sour milk
• pectic acid: found in fruits and some vegetables
• tannic acid: found in tea
• tartaric acid: found in grapes
• oxalic acid: found in spinach

Different Definitions of Acid/Base

The word acid comes from the Latin acidus meaning sour. Chemically though the term acid has a more specific meaning.

The Swedish chemist Svante Arrhenius defined an acid to be a substance that gave up hydrogen ions (H+) when dissolved in water, while bases are substances that give up hydroxide ions (OH-). Notice that this definition limits acids and bases to substances that can dissolve in water. Later on, Bronsted and Lowry defined an acid to be a proton donor and a base to be a proton acceptor. In this definition, even substances that are insoluble in water can be acids and bases. The most general definition of acids and bases is the Lewis definition. A Lewis acid is an electron acceptor, while a Lewis base is an electron donor. Acid/base systems are different from redox reactions in that there is no change in oxidation state.

Acid number

This is used to quantify oxidation. It is the quantity of base, expressed in milligrams of potassium hydroxide, that is required to neutralize the acidic constituents in 1 g of sample.

AN = (V_eq-b_eq)×N×56.1/W_oil ).

V_eq is the amount of titrant (ml) consumed by crude oil sample and 1ml spiking solution at the equivalent point, and b_eqbeq is the amount of titrant (ml) consumed by 1ml spiking solution at the equivalent point.

The molarity concentration of titrant (N) is calculated as such: N = 1000×W_KHP/(204.23×V_eq).

In which, W_KHP is the amount (g) of KHP in 50ml of KHP standard solution, and Veq is the amount of titrant (ml) consumed by 50ml KHP standard solution at the equivalent point.

Acid number (mgKOH/g oil) for biodiesel is preferred to be lower than 3.

Neutralization

Neutralization is a type of reaction between an acid and a base. The products include salt and water. So, it is also called a water forming reaction <math>acid + base \rarr water + salt <math> Example: <math>HCl + Na (OH) \rarr H_2O + NaCl<math>