Acid Chemical Characteristics Characteristics Acids In Food

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.

1 Chemical characteristics

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

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.

2 Characteristics

3 Acids in food

4 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.

The Lewis definition can be explained with molecular orbital theory. In general an acid can receive an electron pair in its lowest unoccupied orbital ( LUMO) from the highest occupied orbital ( HOMO) of a base. That is, the HOMO from the base and the LUMO from the acid combine to a bonding molecular orbital. Simpler definitions are often sufficient for many situations. An acid is often said to be a proton donor, that is the Brønsted definition above. In this case, the proton (H⁺) is the actual acid and the acidity of the proton-donating-compound, called an organic acid, is determined by its stability when it donates protons to the solution it is embedded in. So if the organic acid likes letting protons go, it has high acidity because it donates protons with empty molecular orbitals to the solution. This is how organic acids work, here the Brønsted definition is nice for calculations while the Lewis definition is good for understanding.

5 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 (mg KOH/g oil) for biodiesel is preferred to be lower than 3.

6 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

Home > Acid

1 Chemical characteristics

2 Characteristics

3 Acids in food

4 Different definitions of acid/base

5 Acid number

6 Neutralization

7 Common acids

7.1 Strong inorganic acids

7.2 Strong organic acids

7.3 Weak inorganic acids

7.4 Weak organic acids

Topics: Acid, Chemical Characteristics, Characteristics, Acids In Food...