From the sour taste of lemon to the cleaning power of soap, these substances play a vital role in many fields, from food and health to industry and nature.
Define chemical suppliers, acid, and base
Acids and bases are classified according to their performance in solution.
When acid is dissolved in water, it will release hydrogen ions (H+), thus showing its unique properties, such as being able to react with metals.
Alkali will accept hydrogen ions or release hydroxyl ions (OH), which usually makes people feel greasy and bitter.
There are three main theories to define and describe the difference between chemical suppliers' acid and base:
Arrhenius theory-put forward by Svante Arrhenius in 1884, this theory defines acid as "a substance in rich water or aqueous solution, which can increase the concentration of hydrogen ions (H) in water", while alkali increases the concentration of hydroxyl ions (OH). It is limited to aqueous solution environment, and does not consider the acid-base behavior in non-aqueous solution systems. Bronst-Lohr theory-proposed by Johannes Bronst and Thomas Lohr in 1923, this theory is based on the basis of Arrhenius theory, and defines acid as the donor of proton (H) and alkali as the acceptor of proton. It is suitable for reactions in aqueous and non-aqueous solutions, and includes conjugated acid-base pairs.
Lewis theory-put forward by Gilbert N. Lewis in 1923, defines chemical species as the acceptor of electron pairs and alkali as the donor of electron pairs. It can explain the acid-base interaction without the existence of hydrogen ions, so it is very useful for understanding complex reactions, including those in organic and inorganic chemistry.
How to distinguish acid from alkali
The main feature that distinguishes chemical suppliers' acids from bases lies in their respective pH values. The pH value of an acid is lower than 7, while that of an alkali is higher than 7. This difference can be detected by using a pH meter or an indicator (such as litmus paper).
Litmus test paper is the most commonly used qualitative indicator to distinguish acid from alkali. If it is immersed in an acidic solution, the blue litmus test paper will turn red. On the contrary, if it is immersed in an alkaline solution, the red litmus test paper will turn blue. However, the sensitive range of litmus test paper is limited to the pH value between 4.5 and 8.3.
Other commonly used indicators for detecting chemical suppliers' acids and bases in the laboratory include:
Thymol blue (first change)-turns red in acidic solution and yellow in alkaline solution. Its pH range is 1.2-2.8.
Methyl orange-this indicator turns red in acidic solution and yellow in alkaline solution. Its pH range is 3.2-4.4.
Bromthymol green turns yellow in acidic solution and blue in alkaline solution. Its pH range is 3.8-5.4.
Methyl Red-This indicator has a pH range of 4.8-6.0. It turns yellow when the solution is chemical suppliers acidic, and turns red when it is alkaline or an alkaline solution.
Bromthymol Blue-This indicator has a pH range of 6.0-7.6. It turns yellow when mixed with an acidic solution and blue when mixed with an alkaline solution.
Taste is another remarkable feature of acids and bases. Although we don't recommend tasting tests for strong inorganic acids and bases because they are toxic, you can do such tests for weak organic acids and bases.
For example, you can taste vinegar, which is acetic acid. You can also try baking soda, namely sodium bicarbonate, which is an alkali. Generally speaking, acidic substances taste sour while alkaline substances taste bitter.
As far as the chemical formula is concerned, chemical suppliers' acid exists as a unique component with a hydrogen atom, which will form ions when dissolved in water. Meanwhile, most bases have a hydroxyl (-OH) structure.
Examples of some acids include:
Citric acid-HNO3
Boric acid-H3BO3
Hydrochloric acid-HCl
Sulfuric acid-H2SO4
Meanwhile, some examples of bases include:
Calcium hydroxide-Ca(OH)2
Magnesium hydroxide-Mg(OH)2
Sodium hydroxide-NaOH