What is a base?
-a substance that reacts with an acid to form a salt and water only.
-hydroxides and oxides of metals.
So, what is an alkali?
-a soluble base that produces hydroxide ions (OH-) when dissolved in water.
Important fact
ALL alkalis are BASES BUT NOT all bases are ALKALIS.
Reason?
-because alkali is a base that is soluble in water.
Like acids, there are strong alkalis and weak alkalis.
So, what does it mean to be an strong alkali??
-alkalis that ionise / dissociates completely in water to produce hydroxide ions (OH-). The properties and reactions are due to these hydroxide ions.
Then, what does it mean to be an weak alkali?
-alkalis that ionise / dissociates incompletely / partially in water to produce few hydroxide ions. The reactions are reversible.
From the above explanation, we can conclude that :
Strength of alkali depends of its degree of ionization/dissociation
What are the properties of bases and alkalis?
Bases :
react with acids to form salt and water only.
2. react with ammonium salts to form salt, ammonia and water only.
Alkalis :
bitter taste and soapy feel
2. turn red litmus paper blue.
3. change the colours of the indicators
4.react with a solution of one metal salt to give metal hydroxide and another metal salt.
Fun fact!
What happens when an acid reacts with a base??
Answer : Acids are neutralised by the base!
So, what is neutralisation??
-reaction between an aqueous acid solution and an aqueous alkali solution, the hydrogen ions from the acid combine with the hydroxide ions from the alkali to form water.
-at the same time, heat is given out during the process.
I bet you guys are also interested to know what are some of the uses of bases and alkalis!
Uses :
Ammonia solution:
(a) in window cleaning solutions
(b)in fertilizers
Calcium oxide:
(a) in neutralising acidic solution
(b)to make iron, concrete and cement
Magnesium hydroxide:
(a)in toothpaste to neutralise acid on teeth
(b)in antacids, to relieve digestion
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