(a) What is the pH of 50 mL of a 0.2M glycolic acid aqueous solution after adding 5 mL of 0.25 M KOH? The pKa of glycolic acis is 3.83 at 25 Celsius.
(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 =
K2O - basic
Al(OH)3 - amphoteric
Si(OH)4 - acidic
CaO - basic
what about a?
a) 2.9844
a) 2.9844
b)K2O = basic
Al(OH)3 = amphoteric
Si(OH)4 = acidic
CaO = basic
(a) To calculate the pH of the solution after adding KOH, we need to determine the amount of glycolic acid and KOH that will react and the resulting concentration of the ions present.
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.