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ACIDITIES

Specialty Definition: Acid

(From Wikipedia, the free Encyclopedia)

An acid (from Latin acidus, meaning sour or tart) is a chemical compound generally defined by its reactions with complementary chemicals, designated bases (see Acid-base reaction theories). An acid tends to give a proton and can be represented by the generic formula AH. In water, there is the following reaction:

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

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

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.

Acidity is typically measured using the pH scale.

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

• citric acid: found in citrus fruits
• lactic acid: found in dairy products such as yogurt and sour milk
• carbonic acid: found in carbonated beverages
• acetic acid: found in vinegar

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.

Other meanings

• "Acid" is also a slang word referring to LSD.
• "Acid" is also the sound that a Roland TB-303 music synthesizer makes, and is where the terms Acid Jazz and Acid House originate. A very important term in electronic music, often confused with the LSD meaning.
• ACID is an acronym that expands to four essential properties of a database management system.

  Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Acid."

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ACID

(From Wikipedia, the free Encyclopedia)

In databases, ACID stands for Atomicity, Consistency, Isolation, and Durability. They are considered to be the key transaction processing features of a database management system, or DBMS. Without them, the integrity of the database cannot be guaranteed.

In the context of databases, a single logical operation on the data is called a transaction. A transfer of funds from one account to another is considered a transaction, for example, even though it might consist of multiple tasks (debiting one account and crediting another). The ACID properties guarantee that such transactions are processed reliably.

• Atomicity refers to the ability of the DBMS to guarantee that either all of the tasks of a transaction are performed or none of them are. The transfer of funds can be completed or it can fail for a multitude of reasons, but atomicity guarantees that one account won't be debited if the other is not credited as well.

• Consistency refers to the database being in a legal state when the transaction begins and when it ends. This means that a transaction can't break the rules, or integrity constraints, of the database. If an integrity constraint states that all accounts must have a positive balance, then any transaction violating this rule will be aborted.

• Isolation refers to the ability of the application to make operations in a transaction appear isolated from all other operations. This means that no operation outside the transaction can ever see the data in an intermediate state; a bank manager can see the transferred funds on one account or the other, but never on both -- even if he ran his query while the transfer was still being processed. More formally, isolation means the transaction history is serializable.

• Durability refers to the guarantee that once the user has been notified of success, the transaction will persist, and not be undone. This means it will survive system failure, and that the database system has checked the integrity constraints and won't need to abort the transaction. Typically, all transactions are written into a log that can be played back to recreate the system to the its state right before the failure. A transaction can only be deemed committed after it is safely in the log.

Implementing the ACID properties correctly is not simple. Processing a transaction often requires a number of small changes to be made, including updating indexes that are used by the system to speed up searches. This sequence of operations is subject to failure for a number of reasons; for instance, the system may have no room left on its disk drives.

ACID suggests that the database be able to perform all of these operations at once. In fact this is difficult to arrange. There are two popular families of techniques: Write ahead logging and Shadow paging. In both cases, lockss must be acquired on all information that is read and updated. In write ahead logging, atomicity is guaranteed by ensuring that all REDO and UNDO information is written to a log before it is written to the database. In shadowing, updates are applied to a copy of the database, and the new copy is activated when the transaction commits. The copy refers to unchanged parts of the old version of the database, rather than being an entire duplicate.

In distributed transactions, two-phase commit is typically applied to ensure that each participant on the transaction agree on whether the transaction should be committed or not.

Care must be taken when running transactions in parallel. Two phase locking is typically applied to guarantee full isolation.

The ACID concept is described in ISO/IEC 10026-1:1992 Section 4.

Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "ACID."

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