Question

For the dissociation reaction of a weak acid in water, HA(aq) + H2O(l) ⇌ H3O+(aq) + A−(aq) the equilibrium constant is the acid-dissociation constant, Ka, and takes the form Ka = [H3O+][A−]/[HA] Weak bases accept a proton from water to give the conjugate acid and OH− ions: B(aq) + H2O(l) ⇌ BH+(aq) + OH−(aq) The equilibrium constant Kb is called the base-dissociation constant and can be found by the formula Kb = [BH+][OH−]/[B] When solving equilibrium-based expressions, it is often helpful to keep track of changing concentrations through what is often called an I.C.E table, where I stands for Initial Concentration, C stands for Change, and E stands for Equilibrium Concentration. To create such a table, write the reaction across the top creating the columns, and the rows I.C.E on the left-hand side. Initial (M) .. Change (M) .. Equilibrium (M) .. A + B → AB part a) Aspirin (acetylsalicylic acid, C9H8O4) is a weak monoprotic acid. To determine its acid-dissociation constant, a student dissolved 2.00 g of aspirin in 0.600 L of water and measured the pH. What was the Ka value calculated by the student if the pH of the solution was 2.60? Express your answer numerically using two significant figures. part b) A 0.100 M solution of ethylamine (C2H5NH2) has a pH of 11.87. Calculate the Kb for ethylamine. Express your answer numerically using two significant figures.

          For the dissociation reaction of a weak acid in water,
HA(aq) + H2O(l) ⇌ H3O+(aq) + A−(aq)
the equilibrium constant is the acid-dissociation
constant, Ka, and takes the form
Ka = [H3O+][A−]/[HA]
Weak bases accept a proton from water to give the conjugate acid
and OH− ions: B(aq) + H2O(l) ⇌ BH+(aq) + OH−(aq)
The equilibrium constant Kb is called
the base-dissociation constant and can be found
by the formula Kb = [BH+][OH−]/[B]
When solving equilibrium-based expressions, it is often helpful
to keep track of changing concentrations through what is often
called an I.C.E table, where I stands for Initial Concentration,
C stands for Change, and E stands for Equilibrium Concentration.
To create such a table, write the reaction across the top creating
the columns, and the rows I.C.E on the left-hand side.
Initial (M) .. Change (M) .. Equilibrium (M) ..
A + B → AB

part a) 
Aspirin (acetylsalicylic acid, C9H8O4) is a weak monoprotic
acid. To determine its acid-dissociation constant, a student
dissolved 2.00 g of aspirin in 0.600 L of water
and measured the pH. What was the Ka value
calculated by the student if the pH of the solution was
2.60?
Express your answer numerically using two significant
figures.

part b) 
A 0.100 M solution of ethylamine (C2H5NH2) has
a pH of 11.87. Calculate the Kb for
ethylamine.
Express your answer numerically using two significant
figures.

Added by Patricia A.

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