Free Practice Tests
What is an Alkali?
An alkali is a basic hydroxide or
ionic salt of an alkali metal or alkaline earth metal element, which
is soluble in water. Only few alkalis are known, examples, sodium hydroxide (NaOH),
potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2),
calcium carbonate (CaCO3), and
magnesium hydroxide (Mg(OH)2. Ammonia is also classified as an alkali, though it is not a hydroxide
or ionic salt. This is because ammonia is a very soluble base.
What is an Alkaline Solution?
When an alkali is dissolved in water, the solution
formed is known as alkaline solution. Alkaline solutions can be made in the
laboratory by vigorously shaking a solid alkali in water. They are also formed
through natural processes, such as erosion.
Since alkalis are bases that are soluble in water,
they therefore make it possible for the chemical properties of bases to be
utilized for many purposes in the laboratory, industry, and at home, since almost all - chemical
reactions are carried out in solution.
Properties of Alkaline Solution
The following are properties which alkaline solutions exhibit:
1. They have bitter taste.
2. They turn moist red litmus paper blue.
3. They have soapy or slippery feel.
4. Some are corrosive. Examples, NaOH and KOH.
5. A less volatile alkali displaces a more volatile alkali from its salt. Example, NaOH (less volatile) displaces NH3 (more volatile) from NH4Cl.
NaOH(aq) + NH4Cl(aq) → NaCl(aq) + H2O(l) + NH3(g)
6. React with acids to form salts and water only -
7. Conduct electricity (i.e., they are electrolyte).
8. Show pH values above 7.
Uses of Alkalis
1. NaOH is used in the manufacture of paper, soap and ceramics.
2. Ca(OH)2 (slaked lime, or just “lime”) is added to soils or lakes to make them less acidic.
3. Indigestion may be caused by too much HCl in the stomach, and can be remedied by indigestion tablets which contain such base as MgO or CaCO3 to neutralize the acid.
4. A bee sting is acidic, and can be neutralized by a weak alkali such as ammonia solution.
5. Industrial uses include making various chemicals.
Difference Between Alkali and Base?
A lot of times people wrongly apply the words "alkaline" and "base"
interchangeably to mean the same thing. This is not completely correct. Alkalis
are those bases that can dissolve in water, while those that cannot dissolve in
water are not alkalis. This means that all bases are not alkaline, except those
that can dissolve in water. It is therefore wrong to call all bases alkalis.
The Arrhenius Concept of Bases
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