Based on Bronsted –Lowry Theory, acid is a substance that can donate a proton (H+) to another substance while a base is a substance that can accept a proton (H+) from another substance.
The pH is defined as the negative logarithm of the hydrogen ion, H+ or H3O+ concentration. The hydrogen ion, H+ or [H+] in a solution is measured using a pH scale method.
Salt hydrolysis is the reaction of an anion (-ve ion) or cation (+ve ion) of a salt or both with water.
Buffer solution is a solution which has the ability to maintain its pH when a small amount of strong acid or strong base is added to the solution.
In determining whether a solution is acidic or basic, the pH of the solution is measured. If :
i) The pH is less than 7 (pH < 7), the solution is acidic.
ii) The pH is equal to 7 (pH = 7), the solution is neutral.
iii) The pH is greater than 7 (pH > 7), the solution is basic.
From the result obtained, it can be concluded that hydrochloric acid, HCl and boric acid, H3BO3 are both acidic with pH less than 7 whereas both ammonia, NH3, and sodium hydroxide, NaOH, are basic with pH greater than 7.
sodium carbonate, Na2CO3, is a salt formed from carbonic acid (weak acid) and sodium hydroxide (strong base). Sodium carbonate dissociates completely into sodium ions and carbonate ions. Carbonate ion acts as Bronsted-Lowry base by accepting a proton from water while sodium ion does not react with water because the formation of sodium hydroxide has dissociated completely to Na+ and OH-[1]. The production of OH- from the hydrolysis of CO3 ions causes the solution to be basic.
As for ammonium sulphate, (NH4)2SO4, it is a salt formed from sulphuric acid (strong acid) and ammonia (weak base). Ammonium sulphate dissociates completely into ammonium ions and sulphate ions. Ammonium ion acts as Bronsted-Lowry acid by donating a proton to water molecules whilst sulphate does not give a reaction towards water molecule. The production of H3O+ from the hydrolysis of NH4 causes the solution to be acidic.
Sodium chloride, NaCl, on the other hand is formed from hydrochloric acid (strong acid) and sodium hydroxide (strong base). NaCl dissociates completely into sodium ions and chlorine ions. There is no production of H+ or OH-. Hence, the solution is neutral where both ions will not be hydrolysed by water.
However, the results obtained for Na2CO3 and NaCl does not satisfy the theory due to error in reading the pH meter. The value recorded may be caused by the unstabilized pH value displayed or the solution is not well mixed giving uncertain value of reading.
Hydrochloric acid was added one drop at a time to a buffer solution with pH is 4.70 and to deionized water which is neutral. Both result obtained shows that the pH is slowly becoming more acidic after each addition of hydrochloric acid. But, the pH in buffer solution after adding in each 1.0 M of HCl is likely to have slightly changes with the pH of the buffer solution whereas adding in 1.0 M HCl in deionized water gave a maximize changes to the pH value.
Sodium hydroxide was added one drop at a time to a buffer solution with pH is 4.51 and into deionized water with pH is 7.02. The values outcome presented that the pH is slowly becoming more basic after each addition of 1.0 M NaOH. Addition of 1.0 M NaOH produces the same changes as well as like the addition of 1.0 M HCl to the buffer solution with a minimize change in its pH value. But, the pH obtained when 1.0 M NaOH is added to the deionized water gave a greater change to the pH value.
Buffer solution contains both an acidic and a basic component. Therefore, it will resist changes in pH. When a small amount of acid is added, the H+ ions will be consumed by the acetate ion, CH3COO- to form CH3COOH. As a result, there will be only small change in pH. When a small amount of base is added, the OH- ions will be neutralized by the acid CH3COOH to form CH3COO- and water[3]. Hence, there will be small change in pH value.
Carbon dioxide is an acidic oxide[4] where when it reacts with water, it will form an acid.
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