chem 2

What is the [H+] for a 0.01 M HCl solution?

.01M

What is the Ksp of lead(II) iodide, given that its molar solubility is 1.45 × 10−3 M?

1.22 × 10−8 Ksp = [Pb2+][I−]2, which can be written in terms of molar solubility, s, as Ksp = s(2s)2=4s3=4(1.45×10−3)3 = 1.22 × 10−8.

Which compound is a strong acid?

HNO3

Identify why a weak acid-strong base titration has an equivalence point pH above 7.

The reaction produces a basic salt.

At 25 °C a solution that has a pOH=3 is considered to be _____.

basic

The pH at the equivalence point in a weak base-strong acid titration _____.

less than 7

Calculate the pH of a buffer solution that has an [base]/[acid] ratio of 1.09 if the acid has a pKa of 8.30 at 25 °C.

8.34 Use the equation pH=pKa+log[base][acid] = 8.20 + log(1.09) = 8.34.

Which statement is true for a basic solution at 25 °C?

A basic solution has a pH>7

Which statement is true of strong bases?

A strong base completely dissociates into its component ions in aqueous solution.

What is the Ksp expression of the generic insoluble salt AxBy?

Ksp = [Ay+]x[Bx−]y

What is the conjugate base of H2O?

OH−

Which is the equilibrium equation for the dissolution of lead(II) arsenate? The Ksp expression for lead(II) arsenate is Ksp = [Pb2+]3[AsO43−]2.

Pb3(AsO4)2 (s) ⇌ 3 Pb2+ (aq) + 2 AsO43− (aq)

The pH at the equivalence point of a titration of hydrobromic acid with sodium hydroxide _____.

is equal to 7

The pH at the equivalence point of a titration of hydrochloric acid with sodium hydroxide _____.

is equal to 7

The pH at the equivalence point of a titration of hydrobromic acid with potassium hydroxide _____.

is equal to 7 Hydrobromic acid is a strong acid and potassium hydroxide is a strong base. The equivalence point of a strong acid-strong base titration is always at pH = 7.0. The reason is that the salt, in this case KBr, does not hydrolyze.

At 25 °C a solution that has a pH=7 is considered to be _____.

neutral

An acid and a base that differ by only one _____ are called conjugate acid-base pairs.

proton

At 25 °C a solution that has a pOH<7 is _____.

basic

An acid and a base that differ by only one proton are called _____.

conjugates

There is a point in the titration of a weak acid when the moles of the weak acid are equal to the moles of its conjugate base. This point is known as the _____.

half-equivalence point

The pH at the equivalence point in a weak acid-strong base titration _____.

is greater than 7

A buffer has significant concentrations of both weak acid and conjugate base in equilibrium with each other. weak acid + H2O ⇌ conjugate base + H3O+ When strong acid is added, the equilibrium shifts ____. When strong base is added, the equilibrium shifts

left; right According to Le Châtelier's principle, adding more product will shift the equilibrium left. Adding strong acid is the same as adding H3O+, which is a product of the equilibrium equation. In contrast, removing a product will shift the equilibrium right. Adding strong base is the same as removing H3O+, because the OH− in the strong base reacts with H3O+.

An acid and a base which differ by one _____ are called _____.

proton; conjugate acid-base pairs

Suppose you need a buffer with a pH of 10.9. Which conjugate acid-base pair should you use?

sodium hydrogen carbonate (NaHCO3, pKa = 10.3) and sodium carbonate (Na2CO3) A buffer is most effective within ±1 pH unit of the pKa of the acid. In this case, the pKa is 10.3, so the buffer is effective between 9.3 and 11.3. Since the desired pH of 10.9 falls within this range, this conjugate acid-base pair is a good choice.

Based on its titration curve, identify the analyte in this titration.

strong base (titrated with strong acid)

Calculate the ratio of [sodium formate] to [formic acid] in a buffer solution that has a pH of 3.45. The Ka for formic acid at 25 °C is 1.7 × 10−4.

0.48 pKa=−logKa=−log(1.7×10−4)=3.77 Use the equation pH=pKa+log[base][acid] and solve for [base][acid] [base][acid]=10pH−pKa = 103.45−3.77 = 0.48.

Calculate [KF] in a buffer where [HF] = 0.14 M and pH = 3.90. The Ka for HF at 25 °C is 6.80 × 10−4.

0.76 M pKa=−logKa=−log(6.80×10−4)=3.167Use the equation pH=pKa+log[base][acid] and solve for [base][base]=[acid]⋅10pH−pKa = (0.14 M)103.90−3.167 = 0.75 M.

What is the Ksp of magnesium fluoride if the equilibrium concentrations are [Mg2+] = 2.1 × 10−3 M and [F−] = 4.2 × 10−3 M?

3.7 × 10−8 The Ksp for the dissolution of magnesium fluoride is Ksp = [Mg2+][F−]2. Therefore, Ksp = (2.1 × 10−3)(4.2 × 10−3)2 = 3.7 × 10−8.

Calculate the pH of a buffer containing 0.18 M H2CO3 and 0.25 M NaHCO3. The Ka of H2CO3 at 25 °C is 4.3 × 10−7.

6.51 pKa=−logKa=−log(4.3×10−7)=6.37pH=pKa+log[base][acid]pH = 6.37 + log (0.25/0.18) = 6.51

What is a Brønsted-Lowry acid and base?

A Brønsted-Lowry acid is a proton donor while a Brønsted-Lowry base is a proton acceptor.

What is a Brønsted-Lowry acid?

A Brønsted-Lowry acid is a proton donor.

Which insoluble salt will have a similar solubility in an acidic solution and in a neutral solution?

AgCl

Consider the titration of a weak acid with strong base. Which of the following statements is false about the half-equivalence point?

At the half-equivalence point, the acid is completely neutralized.

Barium forms a variety of insoluble salts, including BaCO3 (Ksp = 5.1 × 10−9), BaSO3 (Ksp = 8.0 × 10−7), BaSO4 (Ksp = 1.1 × 10−10), and BaS2O3 (Ksp = 1.6 × 10−6). Which of these barium salts is the least soluble in water?

BaSO4

Which is the correct equilibrium equation for the dissolution of iron(III) hydroxide? The Ksp expression for iron(III) hydroxide is Ksp=[Fe3+][OH−]3.

Fe(OH)3 (s) ⇌ Fe3+ (aq) + 3 OH− (aq)

Identify the conjugate pair that consists of the acid from the forward reaction and the base from the reverse reaction. H2CO3 + H2O ⇌ HCO3− + H3O+

H2CO3 and HCO3− Conjugates differ by only H+. In the forward reaction, H2CO3 donates H+. In the reverse reaction, HCO3− accepts H+.

Identify the acid in the forward and reverse reactions. NH3 + H2O ⇌ NH4+ + OH−

H2O, NH4+

Identify the conjugate acid-base pair.

H2PO4−, H3PO4

What is the [H3O+] concentration of a 0.0025 M HBr solution?

HBr, hydrobromic acid, is a strong acid which means in dilute solutions it completely dissociates into its component ions of H+ and Br− as shown in the balanced equation HBr → H+ + Br−. For every one mole of HBr, there is one mole of H+ and one mole of Br−. Thus, the concentration of [HBr]=[H+]=[H3O+]=0.0025 M.

Identify the combination that can be used to make a buffer.

HCO2H and NaCO2H

Identify the combination that can be used to make a buffer.

HClO and NaClO

What is the [H+] for a 7.5×10−4 M HI solution?

HI, hydroiodic acid, is a strong acid which dissociates into its component ions of H+ ions and I− ions in solution as shown in the balanced equation HI → H+ + I−. For every one mole of HI, there is one mole of H+ ions and one mole of I− ions. Thus, the concentration of HI is equal to the concentration of H+ ions. [HI]=[H+]=7.5×10−4 M

What is the [OH−] of a 4.2×10−6 M HI solution?

HI, hydroiodic acid, is a strong acid which means in dilute solutions it completely dissociates into its component ions of H+ ions and I− ions as shown in the balanced equation HI → H+ + I−. For every one mole of HI, there is one mole of H+ ions and one mole of I− ions formed. Thus, [HI]=[H+]=[H3O+]=4.2×10−6 M Then, calculate the pH using the formula pH=−log[H3O+]. pH=−log(4.2×10−6 M)=5.4 Next, calculate pOH using the formula 14 = pH + pOH. 14−5.4=8.6 Finally, calculate [OH−] by taking the inverse log of −8.6, thus 10−8.6 =2.4×10−9 M

What is the pOH of a 0.036 M HNO3 solution?

HNO3, nitric acid, is a strong acid which means in dilute solutions it completely dissociates into its component ions of H+ ions and NO3− ions as shown in the balanced equation HNO3 → H+ + NO3−. For every one mole of HNO3, there is one mole of H+ ions and one mole of NO3− ions formed. Thus, the H+ concentration is equal to 0.036 M HNO31L×1 mol of H+1 mol of HNO3=0.036 M [H+] Next, calculate pH by taking the negative log of H+ concentration pH=−log[0.036]=1.4 Finally, calculate pOH by solving the equation pOH=14−pH=12.6

Which statement best describes how a buffer behaves when strong acid or strong base is added?

The pH changes very little when a limited amount of acid or base is added. Buffer solutions are characterized by their ability to resist changes in pH when small amounts of acid or base are added to it.

How will the solubility of AgCl be affected by the addition of a solution of NaCl?

The solubility will decrease.

How will the solubility of ZnS be affected by the addition of a solution of ZnCl2?

The solubility will decrease.

How will the solubility of LiF be affected by the addition of a solution of LiCl?

The solubility will decrease. The dissociation equilibrium reaction for LiF is LiF (s) ⇌ Li+ (aq) + F− (aq). Upon the addition of LiCl, the concentration of Li+ will increase and will therefore shift the equilibrium left toward the formation of more LiF. This will cause a decrease in solubility.

What is the pH of a solution at 25 °C that has a pOH=2.5?

The sum of pH and pOH is equal to 14. Subtract 14−2.5 to find the pH value which is 11.5.

What is the [OH−] concentration for a solution at 25 °C that has a pOH=12.5?

To find the OH− concentration, solve pOH=−log[OH−] by taking the inverse log of −pOH. The inverse log(−12.5)=10−12.5 which equals [OH−]=3.16×10−13 M.

At 25 °C, what is the [H3O+] of a neutral solution?

[H3O+]=1×10−7 M The pH scale is a measure of the H3O+ ions. The greater the concentration of H3O+ ions, the more acidic the solution. When [H3O+]=1×10−7 M, the solution is neutral, and has a pH=7.

At 25 °C a solution that has a [H3O+]=1.0×10−2 M is considered to be _____.

acidic

What is the [H3O+] of a solution at 25 °C with a [OH−] of 9.12×10−5 M?

Solve for the pOH value by taking the negative log of 9.12×10−5 M. The pOH is equal to 4.04. Next, solve for the pH value 14−4.04=9.96=pH Finally, calculate the inverse log of 9.96 to obtain the [H3O+]=1.10×10−10 M.

Which statement best describes how a buffer behaves when strong acid or strong base is added?

The pH changes very little when a limited amount of acid or base is added.

What is the conjugate base of HNO2?

NO2-

What is the conjugate acid of NH3?

NH4+

Which statement is true for a neutral solution at all temperatures?

In a neutral solution, the hydronium ion concentration equals the hydroxide ion concentration ([H3O+]=[OH−]) independent of the temperature. In comparison, the pH of a neutral solution will decrease with increasing temperature. While the pH value decreases with increasing temperature, the solution is still neutral because [H3O+]=[OH−].

What is the pOH of a 2.3×10−9 M KOH solution?

KOH, potassium hydroxide, is a strong base which means in dilute solutions the KOH completely dissociates into its component ions of K+ and OH− as shown in the balanced equation KOH → K+ + OH−. For every one mole of KOH, there is one mole of K+ ions and one mole of OH− ions that are formed as per the coefficients of the balanced chemical equation. The OH− ion concentration is equal to 2.3×10−9 mol of KOH1L×1 mol of OH−1 mol of KOH=2.3×10−9 M OH−. Determine the pOH value by taking the negative log of OH− concentration which is −log[2.3×10−9]=8.6=pOH.