K2O - basic
Al(OH)3 - amphoteric
Si(OH)4 - acidic
CaO - basic
(b) Classify each of the following compounds as either "acidic", "basic", or "amphoteric" (able to act as either an acid or a base).
i)K2O =
ii) Al(OH)3 =
iii) Si(OH)4 =
iv) CaO =
Al(OH)3 - amphoteric
Si(OH)4 - acidic
CaO - basic
b)K2O = basic
Al(OH)3 = amphoteric
Si(OH)4 = acidic
CaO = basic
First, let's calculate the moles of glycolic acid and KOH used:
Moles of glycolic acid: 0.2 M x 0.05 L = 0.01 moles
Moles of KOH: 0.25 M x 0.005 L = 0.00125 moles
Since KOH is a strong base, it will completely dissociate into its ions, providing hydroxide ions (OH-) to react with the glycolic acid. The balanced chemical equation for this reaction is:
HOCOOH (glycolic acid) + OH- (from KOH) → HOCOO- (glycolate ion) + H2O
From the balanced equation, we can see that the stoichiometric ratio is 1:1 between glycolic acid and OH-. Therefore, all 0.01 moles of glycolic acid will react with 0.01 moles of OH-.
Now, let's calculate the concentration of OH- ions after the reaction:
OH- concentration after reaction = (0.00125 moles OH-) / (0.05 L + 0.005 L) = 0.025 M
Since pKa is given for the glycolic acid, we can use the Henderson-Hasselbalch equation to calculate the pH:
pH = pKa + log([A-]/[HA])
Since the volume changed due to adding KOH, we need to recalculate the concentrations of glycolic acid and glycolate ion.
Concentration of glycolic acid after reaction:
Initial concentration - reacting moles / total volume = (0.2 M x 0.05 L - 0.01 moles) / (0.05 L + 0.005 L) = 0.18 M
Concentration of glycolate ion:
Reaction moles / total volume = 0.01 moles / (0.05 L + 0.005 L) = 0.2 M
Plugging the values into the Henderson-Hasselbalch equation:
pH = 3.83 + log(0.2 M / 0.18 M)
Solving this equation will give you the pH of the solution after adding KOH.
(b) Let's classify each compound as acidic, basic, or amphoteric:
i) K2O (potassium oxide) - This compound is basic because it consists of a metal (potassium) and oxygen. Metal oxides typically react with water to form bases.
ii) Al(OH)3 (aluminum hydroxide) - This compound is amphoteric because it can act as both an acid and a base. It can donate protons (act as an acid) by losing hydroxide ions, or accept protons (act as a base) by gaining hydroxide ions.
iii) Si(OH)4 (silicic acid or orthosilicic acid) - This compound is acidic. It contains hydrogen atoms bonded to oxygen, indicating its potential to donate protons (act as an acid).
iv) CaO (calcium oxide) - This compound is basic as it is an oxide of a metal (calcium). Metal oxides are generally basic and can react with water to form bases.