The Alkaline solutions Are formed when an alkali is dissolved in water. An alkaline solution can be synthesized in the laboratory and can also be formed in natural processes such as erosion.
Examples of alkaline solutions include sodium hydroxide, potassium hydroxide, magnesium hydroxide and calcium carbonate. Each of these solutions has different applications in different industries (What is an Alkali?, S.F.).
An alkaline solution may be sodium hydroxide
Manufacturers commonly use alkaline solutions in products such as biofuels, soaps, medicines, detergents and cleaning products, as well as In many food preparations and specialized applications. As cleaning agents alkaline solutions can dissolve fats, oils and proteins (ADAMS, 2015).
Bases and alkalis to understand alkaline solutions
Base, in chemistry, refers to any substance that in the aqueous solution is slippery to the touch, tastes bitter, changes the color of the indicators (for example, converts the litmus paper from red to blue as illustrated in Figure 1), reacts With acids to form salts and promotes certain chemical reactions.
Examples of bases are the hydroxides of the alkali and alkaline earth metals (sodium, calcium, etc.) and the aqueous solutions of ammonia or its organic derivatives (amines). Such substances produce hydroxide ions (OH-) (Britannica, Base chemical compound, 2010). There are different types of classifications for both acids and bases:
Figure 1: The indicator paper used to determine the pH of a liquid. The paper turns blue when a solution is a base.
According to Arrhenius's theory, bases are substances that dissociate in water to produce electrically charged atoms or molecules, called hydroxide ions (OH-) (Britannica, Arrhenius theory, 1998).
The Brønsted-Lowry theory, also called the proton theory of acids and bases, introduced independently in 1923 by the Danish chemist Johannes Nicolaus Brønsted and the English chemist Thomas Martin Lowry, indicates that any compound that can accept one proton (H +) from another Compound is a base. For example in the reaction:
Ammonia would be a base since it accepts protons of hydrochloric acid (Britannica, Brønsted-Lowry theory, 1998).
The Lewis Theory of Acids and Bases introduced in 1923 states that a base is considered to be any compound possessing a pair of available non-shared electrons and is capable of binding to a substance that is capable of accepting them (Lewis acid).
Nitrogen from ammonia and oxygen in water are examples of Lewis bases (Britannica, Lewis theory, 1998).
The terms"basic solution"and"alkaline solution"are often used interchangeably, particularly outside the context of chemistry.
Alkalis are generally defined as a subset of the bases. It is a basic hydroxide or an ionic salt of an alkali metal or alkaline earth metal element, which is soluble in water forming an alkaline solution.
Only few alkalis are known, such as sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca (OH) 2 ), Calcium carbonate (CaCO 3 ) And magnesium hydroxide (Mg (OH) 2 ). Alkalis exclude bases such as NH 3 Or solutions such as ammonium hydroxide, since they are not formed by alkali or alkaline earth metals.
Alkaline solutions and their relationship to pH
Hydrogen potential, also known as pH scale, measures the alkalinity or acidity level of a solution. The scale varies from zero to 14, acid being a pH less than 7 and basic a pH greater than 7.
The midpoint 7 represents a neutral pH. A neutral solution is neither acid nor alkaline. The pH scale is obtained as a function of the concentration of H + in the solution.
The pH scale is logarithmic and as a result, each integer pH value below 7 is ten times more acidic than the next higher value. For example, pH 4 is ten times more acidic than pH 5 and 100 times (10 times 10) more acid than pH 6.
The same is true for pH values greater than 7, each of which is ten times more alkaline (another form of saying basic) than the next lower integer value. For example, pH 10 is ten times more alkaline than pH 9 and 100 times (10 times 10) more alkaline than pH 8 (pH Scale, S.F.).
Figure 2: pH scale.
Similarly, a scale of pOH is obtained as a function of the OH concentration and is inversely related to the pH scale (pH, pOH, and the pH scale, S.F.).
A characteristic property of alkaline solutions is that, by producing OH- ions, the pH of a solution increases to values greater than 7 (or decrease the pOH to values less than 7).
Properties
The following are properties of alkaline solutions:
- They taste bitter.
- The litmus paper changes to blue.
- They have a soapy or slippery feel to the touch.
- Some are corrosive. Examples, NaOH and KOH.
- A less volatile alkali displaces a more volatile alkali of its salt. Example, NaOH (less volatile) displaces NH 3 (More volatile) from NH 4 Cl.
NaOH (aq) + NH 4 Cl (aq) → NaCl (aq) + H 2 O (1) + NH 3 (G)
- React with acids to form salts and water (neutralization reaction).
- They conduct electricity (ie they are electrolytes).
- They show pH values above 7.
Applications
Since alkalis are bases that are soluble in water, they make it possible for the chemical properties of the bases to be used for many purposes in the laboratory, industry and at home, since almost all chemical reactions are carried out in solution .
- NaOH is used in the manufacture of paper, soap and ceramics.
- Add Ca (OH) 2 (slaked lime or simply"lime") to soils or lakes to make them less acidic.
- Indigestion is usually caused by excess HCl in the stomach and may be remedied by indigestion tablets containing a base such as MgO or CaCO3 to neutralize the acid.
- Industrial uses include the manufacture of various chemicals.
- They are used in oxide-reduction reactions to establish the basic medium where the reaction occurs.
References
- ADAMS, A. (2015, June 17). What is an Alkaline Solution? Taken from livestrong.com.
- Britannica, T. E. (1998, December 21). Arrhenius theory. Taken from britannica.com.
- Britannica, T. E. (1998, July 20). Brønsted-Lowry theory. Taken from britannica.com.
- Britannica, T. E. (1998, July 20). Lewis theory. Retrieved from britannica.com.
- Britannica, T. E. (2010, April 27). Base chemical compound. Taken from britannica.com.
- PH Scale. (S.F.). Retrieved fromchemistry.elmhurst.edu.
- PH, pOH, and the pH scale. (S.F.). Taken from khanacademy.org.
- What is an Alkali? (S.F.). Taken from freechemistryonline.com.