4.4 Practice Problems#
Label each species in the reactions below as acid, base, conjugate base, or conjugate acid:
Calculate \([\ce{OH-}]\) in a \(\pu{1.4e-3 M}\) \(\ce{HCl}\) solution at \(\pu{25 ^\circ C}\).
Calculate \([\ce{H3O+}]\) in a solution for which \([\ce{OH-}] = \pu{0.25 M}\) at \(\pu{25 ^\circ C}\).
Calculate the concentration of the strong acid, \(\ce{HBr}\), in a solution at \(\pu{25 ^\circ C}\) that has a \(p\ce{H}\) of
\(0.12\)
\(2.46\)
\(6.27\)
A sample of acid rain collected from a pond was shown to have a \(p\ce{H} = 4.65\). What concentration of \(\ce{HNO3}\) is this \(p\ce{H}\) equivalent to?
Calculate the concentration of \(\ce{HCl}\) in a solution at \(\pu{25 ^\circ C}\) that has \(p\ce{H} =\)
\(4.95\)
\(3.45\)
\(2.78\)
An aqueous solution of a strong base has \(p\ce{H} = 8.15\) at \(\pu{25 ^\circ C}\). Calculate the original concentration of the base in the solution if the base is
\(\ce{NaOH}\)
\(\ce{Ba(OH)2}\)
Calculate the \(p\ce{H}\) of an aqueous solution at \(\pu{25 ^\circ C}\) that is \(\pu{0.095 M}\) in hydrocyanic acid (\(\ce{HCN}\)). (\(K_a = \pu{4.9e-10}\))
Calculate the equilibrium \(p\ce{H}\) of \(\pu{0.0075 M}\) \(\ce{HClO}\) (hypochlorous acid, the main ingredient of bleach) solution at \(\pu{25 ^\circ C}\). This equilibrium reaction is
The \(p\ce{H}\) of an aqueous acid solution is \(\pu{6.20}\) at \(\pu{25 ^\circ C}\). Calculate \(K_a\) for this acid if the initial acid concentration is \(\pu{0.010 M}\). Assume the acid to be a weak monoprotic acid.
Using the acetic acid equilibrium reaction as shown below, determine the \(p\ce{H}\) and percent ionization for acetic acid (\(\ce{CH3COOH}\)) solutions at \(\pu{25 ^\circ C}\) with concentrations :
\(\pu{0.15 M}\)
\(\pu{0.015 M}\)
\(\pu{0.0015 M}\)
In the following dissociation reaction of \(\ce{H4SiO4 (aq)}\), calculate the relative abundance of \(\ce{H4SiO4 (aq)}\) to \(\ce{H3SiO4- (aq)}\) at \(p\ce{H} = 8.2\) at \(\pu{25 ^\circ C}\).
Solve the following problems that are related to the carbonate system:
In a natural water whose \(p\ce{H} = 4\) at \(\pu{25 ^\circ C}\), calculate the relative activity of (a) \(\ce{H2CO3^* (aq)}\) to \(\ce{HCO3- (aq)}\) and (b) \(\ce{HCO3- (aq)}\) to \(\ce{CO3^2- (aq)}\).
Determine the \(p\ce{H}\) at which (a) \([\ce{H2CO3^* (aq)}] = [\ce{HCO3- (aq)}]\) and (b) \([\ce{HCO3- (aq)}] = [\ce{CO3^2- (aq)}]\).
A groundwater sample has \(p\ce{H} = 6.84\) and \([\ce{HCO3- (aq)}] = \pu{460 mg L−1}\). Calculate \(P_\ce{CO2 (g)}\) at \(\pu{25 ^\circ C}\). Assume that activity equals concentration.
Calculate \(p\ce{H}\) of rainwater in equilibrium with atmospheric \(\ce{CO2}\).
Calculate the concentration of each carbonate species in solution at \(\pu{25 ^\circ C}\) when \(\ce{C}_T = \pu{e-3 mol L-1}\) and \(p\ce{H} = 5.7\). Explain if your answer is reasonable.
Calculate the acidity and alkalinity of this system at \(\ce{C}_T = \pu{e-3 mol L-1}\) and \(p\ce{H} = 5.7\).
Solve the following problems that are related to the silicate system:
In a natural water whose \(p\ce{H} = 7\) at \(\pu{25 ^\circ C}\), calculate the relative abundance of \(\ce{H4SiO4 (aq)}\) to \(\ce{H3SiO4- (aq)}\).
Determine the \(p\ce{H}\) at which (a) \([\ce{H4SiO4 (aq)}] = [\ce{H3SiO4- (aq)}]\) and (b) \([\ce{H3SiO4- (aq)}] = [\ce{H2SiO4^2- (aq)}]\).
A river water sample has a \(p\ce{H}\) of 6.5 and \(\ce{Si}_T = \pu{10.5 mg L−1}\). Calculate each silica species concentration in this water sample. Note: Use the same method as that used for the carbonate system.
Calculate the concentration of \(\ce{OH-}\) in solution if \(\pu{0.1 mol}\) of \(\ce{NH3}\) is dissolved in \(\pu{1 L}\) of pure water at \(\pu{25 ^\circ C}\). (\(K_b = \pu{10^{-4.7}}\))
What is the original molarity of an aqueous solution of ammonia (\(\ce{NH3}\)) whose \(p\ce{H}\) is \(11.22\) at \(\pu{25 ^\circ C}\)?
\(\ce{Zn(OH)2 (s)}\) is an amphoteric hydroxide. Write balanced ionic equations to show its reaction with
\(\ce{HCl}\)
\(\ce{NaOH}\) (note: the product is \(\ce{Zn(OH)4^2- (aq)}\)).
\(\ce{Cu(OH)2 (s)}\) is an amphoteric compound and dissolves according to the shown after the question. Answer the following questions and assume that the water temperature is \(\pu{25 ^\circ C}\).
Excess copper hydroxide is added to a beaker of water, i.e., solid copper hydroxide is present in the water. The solution \(p\ce{H}\) is adjusted to \(10\) using a base. Calculate \([\ce{Cu(OH)3- (aq)}]\) in the solution at equilibrium.
A strong acid is added to the solution until the \(p\ce{H}\) is reduced to \(4\). Will the amount of \(\ce{Cu(OH)3- (aq)}\) in the beaker increase or decrease? Explain. At this \(p\ce{H}\), calculate \([\ce{Cu(OH)3- (aq)}]\) in the solution.
Calculate the \(p\ce{H}\) of a buffer system made up of \(\pu{0.15 M}\) \(\ce{NH3}\) and \(\pu{0.35 M}\) \(\ce{NH4Cl}\). \(pK_a= 9.26\) for \(\ce{NH4+}/\ce{NH3}\).
What is the \(p\ce{H}\) of the buffer that is made up of \(\pu{0.10 M}\) of \(\ce{Na2HPO4}\) and \(\pu{0.15 M}\) of \(\ce{KH2PO4}\)? \(pK_a\)’s for the dissociation of the weak acid, \(\ce{H3PO4}\) are \(2.15\), \(7.20\), and \(12.35\).
If \(\pu{0.10 M}\) \(\ce{NaOH}\) is added to a buffer solution containing \(\pu{1 M}\) each of \(\ce{CH3COOH}\) and \(\ce{CH3COONa}\), determine the final solution \(p\ce{H}\).
The \(p\ce{H}\) of a bicarbonate-carbonic acid buffer is \(8.0\). Calculate the ratio of the concentration of carbonic acid (\(\ce{H2CO3}\)) to that of the bicarbonate ion (\(\ce{HCO3-}\)).
In a natural water sample that is in equilibrium with atmospheric \(\ce{CO2}\) and an initial \(p\ce{H}\) of \(6.35\), determine the change in \(p\ce{H}\) upon the addition of a strong acid at the following concentrations: (Note: The activity of \(\ce{CO3^2-}\) is negligible.)
\(\pu{e-3 mol}\)
\(\pu{e-4 mol}\)
\(\pu{e-5 mol}\)
A water sample from the Rio Grande River in Texas has \([\ce{Ca^2+}] = \pu{109 mg L-1}\) and \([\ce{SO4^2-}] = \pu{238 mg L-1}\) in addition to other ions. Is this water under-, over-, or saturated with respect to gypsum (\(K_{s0} = 10^{-4.6}\))?