What is acid base indicator

Chemists or chemistry texts often use the hydrogen ion, H + to show a hydrogen ion released into water solution. In a way, there is no such thing as a hydrogen ion or proton without anything else. The majority of hydrogen atoms are only a single proton and a single electron. If you remove the electron to make it an ion, the only thing that is left is a proton. Protons just don't exist naked like that in water solution. Remember that water is a very polar material. There is a strong partial negative charge on the side of the oxygen atom and a strong partial positive charge on the hydrogen side. Any loose hydrogen ion, having a positive charge, would quickly find itself near the oxygen of a water molecule. At close range from the charge attraction, the hydrogen ion would find a pair (its choice of two pairs) of unshared electrons around the oxygen that would be capable of filling the its outer shell. Each hydrogen ion unites with a water molecule to produce a hydronium ion . (H3 O) + . the real species that acts as acid. The hydroxide ion in solution does not combine with a water molecule in any similar fashion. As we write reactions of acids and bases, it is usually most convenient to ignore the hydronium ion in favor of writing just a hydrogen ion, H + .


For the properties of acids and bases we will use the Arrhenius definitions.

Acids release a hydrogen ion into water (aqueous) solution . You will usually see the formula for an acid with the ionizable hydrogen at the beginning, such as HCl, hydrochloric acid, or H(C2 H3 O2 ), acetic acid.

Acids neutralize bases in a neutralization reaction . An acid and a base combine to make a salt and water. A salt is any ionic compound that could be made with the anion of an acid and the cation of a base. The hydrogen ion of the acid and the hydroxide ion of the base unite to form water.

Acids corrode active metals . Even gold, the least active metal, is attacked by an acid, a mixture of acids called 'aqua regia,' or 'royal liquid.' When an acid reacts with a metal, it produces a compound with the cation of the metal and the anion of the acid and hydrogen gas.

Acids turn blue litmus to red . Litmus is one of a large number of organic compounds that change colors when a solution changes acidity at a particular point. Litmus is the oldest known pH indicator. It is red in acid and blue in base. The phrase, 'litmus test,' indicates that litmus has been around a long time in the English language. Litmus does not change color exactly at the neutral point between acid and base, but very close to it. Litmus is often impregnated onto paper to make 'litmus paper.'

Acids taste sour . TASTING LAB ACIDS IS NOT PERMITTED BY ANY SCHOOL. The word 'sauer' in German means acid and is pronounced almost exactly the same way as 'sour' in English. (Sauerkraut is sour cabbage, cabbage preserved in its own fermented lactic acid. http://en.wikipedia.org/wiki/Sauerkraut http://www.wildfermentation.com/resources.php?page=sauerkraut ) Stomach acid is hydrochloric acid. Although tasting stomach acid is not pleasant, it has the sour taste of acid. Acetic acid is the acid ingredient in vinegar. Citrus fruits such as lemons, grapefruit, oranges, and limes have citric acid in the juice. Sour milk, sour cream, yogurt, kimchi, and cottage cheese have lactic acid from the fermentation of the sugar lactose.


Bases release a hydroxide ion into water solution . (Or, in the Lowry - Brшnsted model, cause a hydroxide ion to be released into water solution by accepting a hydrogen ion in water.)

Bases neutralize acids in a neutralization reaction . The word - reaction is: Acid plus base makes water plus a salt.

Where 'Y' is the anion of acid 'HY,' and 'X' is the cation of base 'XOH,' and 'XY' is the salt in the product, the reaction is: HY + XOH

"> HOH

+ XY

Bases denature protein . This accounts for the "slippery" feeling on hands when exposed to base. Strong bases that dissolve in water well, such as sodium or potassium lye are very dangerous because a great amount of the structural material of human beings is made of protein. Serious damage to flesh can be avoided by careful use of strong bases.

Bases turn red litmus to blue . This is not to say that litmus is the only acid - base indicator, but that it is likely the oldest one.

Bases taste bitter . There are very few food materials that are alkaline, but those that are taste bitter. It is even more important that care be taken in tasting bases. Again, NO SCHOOL PERMITS TASTING OF LAB CHEMICALS. Tasting of bases is more dangerous than tasting acids due to the property of stronger bases to denature protein.


The common acids that are almost one hundred percent ionized are:

The acids on this short list are called strong acids . because the amount of acid quality of a solution depends upon the concentration of ionized hydrogens. Muriatic acid is the name given to an industrial grade of hydrochloric acid that is often used in the finishing of concrete. Less concentated hydrochloric acid can be found in the human stomach. Strong acids are completely ionized in water. You are not likely to see much HBr or HI in the lab because they are expensive. You are not likely to see perchloric acid in a school setting because it can explode if not treated carefully. Other acids are incompletely ionized, existing mostly as the unionized form. Incompletely ionized acids are called weak acids . because there is a smaller concentration of ionized hydrogens available in the solution. Do not confuse this terminology with the concentration of acids. The differences in concentration of the entire acid will be termed dilute or concentrated .

Likewise, there is a short list of strong bases, ones that completely ionize into hydroxide ions and a conjugate acid. All of the bases of Group I and Group II metals except for beryllium are strong bases . Again, like the strong acids, the strong bases are completely ionized in water solution. Lithium, rubidium and cesium hydroxides are not often used in the lab because they are expensive. The bases of Group II metals, magnesium, calcium, barium, and strontium are strong, but all of these bases have somewhat limited solubility. Barium hydroxide has a high enough solubility to really call it the only dibasic strong base. Magnesium hydroxide has a particularly small solubility. Potassium and sodium hydroxides both have the common name of lye . Soda lye (NaOH) and potash lye (KOH) are common names to distinguish the two compounds.

The bases of Group I metals are all monobasic . The bases of Group II metals are all dibasic . Aluminum hydroxide, Al(OH) 3 is tribasic . Any material with two or more ionizable hydroxyl groups would be called polybasic . Most of the alkaline organic compounds (and some inorganic materials) have an amino group -(NH2 ) rather than an ionizable hydroxyl group. The amino group attracts a proton (hydrogen ion) to become -(NH3 ) + . (The dash before the (NH3 ) + or (NH2 ) indicates a single bonding electron, so this is attached to something else by a covalent bond.) By the Lowry- Brшnsted definition, an amino group definitely acts as a base, and the effect of removing hydrogen ions from water molecules is the same as adding hydroxide ions to the solution.

Memorize the strong acids and strong bases. All other acids or bases are weak.


It is important to notice that just because a compound has a hydrogen or an -OH group as a part of the structure does not mean that it can be an acid or a base. The hydrogens of methane, CH4 . are all very covalently attached to the carbon atom, and the hydrogens do not ionize, so methane is not an acid. Glycerin (or glycerol) has three -OH groups in its structure, but the -OH groups do not separate as an ion, so glycerin is not a base.

Source: www.chemtutor.com

Category: Forex

Similar articles: