Assignment 9: 15.9- 16.3

Calculate the pH of the solution upon the addition of 10.0 mL of 1.00 M HCl to the original buffer. Express the pH to two decimal places.

pH = 4.66

Calculate the pH of the solution upon the addition of 0.015 mol of NaOH to the original buffer. Express the pH to two decimal places.

pH = 4.88

What is the pH after 0.150 mol of HCl is added to the buffer from Part A? Assume no volume change on the addition of the acid. Express the pH numerically to three decimal places.

pH = 6.165

What is the pH of a buffer prepared by adding 0.405 mol of the weak acid HA to 0.609 mol of NaA in 2.00 L of solution? The dissociation constant Ka of HA is 5.66×10−7. Express the pH numerically to three decimal places.

pH = 6.424

What is the pH after 0.195 mol of NaOH is added to the buffer from Part A? Assume no volume change on the addition of the base. Express the pH numerically to three decimal places.

pH = 6.830

Calculate the pH of the solution made by adding 0.50 mol of HOBr and 0.30 mol of KOBr to 1.00 L of water. The value of Ka for HOBr is 2.0×10−9. Express your answer numerically using two decimal places.

pH = 8.48

What is the effective pH range of a buffer (relative to the pKa of the weak acid component)?

pKa±1

Write chemical equations for second ionization step of phosphoric acid. Express your answer as a chemical equation. Identify all of the phases in your answer.

H2PO4−(aq)+H2O(l)⇌HPO42−(aq)+H3O+(aq)

Write chemical equations for first ionization step of phosphoric acid. Express your answer as a chemical equation. Identify all of the phases in your answer.

H3PO4(aq)+H2O(l)⇌H2PO4−(aq)+H3O+(aq)

Which of the pairs below would be the best choice for a pH 5 buffer? HF/NaF, K a (HF) = 3.5 × 10-4 HC2H3O2/KC2H3O2, K a (HC2H3O2) = 1.8 × 10-5 NH3/NH4Cl, K b (NH3) = 1.8 × 10-5

HC2H3O2/KC2H3O2 is best.

Write chemical equations for third ionization step of phosphoric acid. Express your answer as a chemical equation. Identify all of the phases in your answer.

HPO42−(aq)+H2O(l)⇌PO43−(aq)+H3O+(aq)

Rank the following compounds in order of decreasing acid strength using periodic trends. Rank the acids from strongest to weakest. To rank items as equivalent, overlap them.

Strongest to Weakest Acid: HBr, HCl, H2O, LiH

You need to produce a buffer solution that has a pH of 5.33. You already have a solution that contains 10. mmol (millimoles) of acetic acid. How many millimoles of acetate (the conjugate base of acetic acid) will you need to add to this solution? The pKa of acetic acid is 4.74. Express your answer numerically in millimoles.

39 mmol acetate

Which buffer component would you add to change the pH of the buffer to 4.72?

A-

Using the Arrhenius concept of acids and bases, identify the Arrhenius acid and base in each of the following reactions: 2KOH(aq)+H2SO4(aq)→K2SO4(aq)+2H2O(l) NH3(g)+HCl(g)→NH4Cl(s) Drag the appropriate items to their respective bins.

Arrhenius acid = H2SO4 Arrhenius base = KOH Neither= NH3, HCl

Using the Brønsted-Lowry concept of acids and bases, identify the Brønsted-Lowry acid and base in each of the following reactions: HSO4−(aq)+H2O(l)→H2SO4(aq)+OH−(aq) CH3NH2(g)+BBr3(g)→CH3NH2BBr3(s) Drag the appropriate items to their respective bins.

Bronsted- Lowry acid= H2O Bronsted- Lowry base= HSO4- Neither= CH3NH2, BBr3

Using the Lewis concept of acids and bases, identify the Lewis acid and base in each of the following reactions: Al(NO3)3(s)+6H2O(l)→Al(H2O)63+(aq)+3NO3−(aq) (CH3)2NH(g)+HF(g)→(CH3)2NH2F(s) Drag the appropriate items to their respective bins.

Lewis Acid= Al(NO3)3, HF Lewis Base= (CH3)2NH, H2O Neither = none

Without consulting the table of acid-dissociation constants, match the following acids to the given Ka1 values. Drag the appropriate items to their respective bins.

Ka1= 1.7x10^-7 H2S Ka1= 1.7x10^-2 H2SO3 Ka1= very large H2SO4

Write corresponding equilibrium expressions for first ionization step of phosphoric acid.

Ka1=[H3O+][H2PO−4]/[H3PO4]

Write corresponding equilibrium expressions for second ionization step of phosphoric acid.

Ka2=[H3O+]/ [HPO2−4][H2PO−4]

Write corresponding equilibrium expressions for third ionization step of phosphoric acid.

Ka3=[H3O+][PO3−4]/ [HPO2−4]

Calculate the concentration of H+ ions in a 0.010 M aqueous solution of sulfuric acid. Express your answer to three decimal places and include the appropriate units.

[H+] = 0.015 M

Ka1=1.0×10−4;Ka2=1.0×10−6 Express your answers using two significant figures separated by commas.

[H3O+]1, [H3O+]2 = 3.1×10−3,1.0×10−6

Consider a 0.10 M solution of a weak polyprotic acid (H2A) with the possible values of Ka1 and Ka2 given below. Calculate the contributions to [H3O+] from each ionization step. Ka1=1.0×10−4;Ka2=5.0×10−5 Express your answers using two significant figures separated by commas.

[H3O+]1, [H3O+]2 = 3.1×10−3,4.8×10−5

Ka1=1.0×10−4;Ka2=1.0×10−5 Express your answers using two significant figures separated by commas.

[H3O+]1, [H3O+]2 = 3.1×10−3,9.9×10−6

A buffer contains the weak acid HA and its conjugate base A−. The weak acid has a pKa of 4.82 and the buffer has a pH of 4.25. Which statement is true of the relative concentrations of the weak acid and conjugate base in the buffer?

[HA] > [A−]

Calculate the concentration of HSO4− ions in a 0.010 M aqueous solution of sulfuric acid. Express your answer to two significant figures and include the appropriate units.

[HSO4−] = 5.5×10−3 M

Calculate the concentration of SO42− ions in a 0.010 M aqueous solution of sulfuric acid. Express your answer to four decimal places and include the appropriate units.

[SO42−] = 0.0045 M

Which solution is a buffer?

a solution that is 0.100 M in HNO2 and 0.100 M in NaNO2

A 1.0 L buffer solution is 0.12 M in HNO2 and 0.060 M in KNO2. Which action destroys the buffer?

adding 0.060 mol of HNO3