- Bases react with acids to form a salt and water only (neutralization).
- Bases react with ammonium salts to produce ammonia gas, water and salt.
Category: Acids and Bases
List down the three acidic chemical properties.
- Acids react with reactive metals to form hydrogen and salt.
- Acids react with carbonates to form a salt, carbon dioxide and water.
- Acids react with bases to form a salt and water only (neutralization).
Acid-Base Titration
Define “tribasic weak acid”.
“Tribasic” means one mole of the acid will dissociate in water to produce 3 moles of hydrogen ions.
“weak acid” means that the acid molecules dissociate partially when dissolved in water to produce a low concentration of hydrogen ions.
What is a buffer solution?
A buffer is an aqueous solution that can resist significant changes in pH levels upon the addition of a small amount of acid or alkali.
There are two types of buffer solutions: acidic buffer and alkaline buffer.
Acidic buffer
Acid buffer solutions have a pH less than 7. It is generally made from a weak acid and one of its salts. Commonly used acidic buffer solutions are a mixture of ethanoic acid (a weak acid) and sodium ethanoate in solution (a weak basic salt), which have a pH of 4.76 when mixed in equal molar concentrations.
Alkaline buffer
Alkaline buffer solutions have a pH greater than 7 and are made from a weak base and one of its salts. A very commonly used example of an alkaline buffer solution is a mixture of ammonia (weak alkali) and ammonium chloride solution (a weak acidic salt). If these were mixed in equal molar proportions, the solution would have a pH of 9.25.
How do buffers work?
Buffers work by neutralizing any added acid (H+ ions) or base (OH- ions), by producing a weak acid or a weak alkali, respectively, hence maintaining the required pH.
For example, a buffer made up of the weak base ammonia, NH3 and its conjugate acid, NH4+. When HCl (strong acid) is added to this buffer system, the extra H+ ions added to the system are consumed by the NH3 to form NH4+, which is a weak acid. Now, because all the extra H+ ions are locked up and have formed a weaker acid, NH4+, thus the pH of the system does not change significantly. Similarly, when NaOH (strong base) is added to this buffer system, the NH4+ ion donates a proton to the base to become ammonia and water, which is a weak alkali, thus neutralizing the base without any significant pH change.
H2O (l) + NH3 (g) ⇌ OH– (aq) + NH4+ (aq)
Example:
Answer is A. The mixture of ammonia and ammonium chloride solution acts as an alkaline buffer solution, maintaining the pH at about 10.
Explain why it is not advisable for farmers to add slaked lime and ammonium-based fertilizers to their crop soil at the same time.
When both substances are added at the same time, they will react to produce a salt, ammonia gas and water.
Slaked lime will be used up in the reaction, hence the acidity of the soil will not be reduced.
Fertilizers will be used up in the reaction. Ammonia gas produced will escape to the surroundings, so nitrogen element, which is needed by the plants for healthy growth, will not be absorbed by the plants.