Acid base buffers, titrations and Ksp F23

Which of the following combinations will form a buffer solution? Select all that apply.

• HCOOH and LiCOOH

• NH₃ and NH₄Br

• KOH and KF

• HCl and RbOH

Answer explanation

A buffer is

1) a weak acid (HA) & a salt w/ it's conjugate base (A-).

2) a weak base (B) and a salt w/ it's C.A. (HB+).

What is the pH of a buffer mixture of 0.70 M KCH₃COO and 0.50 M CH₃COOH (K_a = 1.8x10^-5)?

• 0.30

• 4.89

• 4.60

• 4.74

• 0.45

Answer explanation

If you have a buffer, what equation can you use?

The salt and acid don't react! The salt provides a common ion (A-).

Which is the net ionic equation when NaOH(aq) is added to HF(aq) ?

Answer explanation

Don't split a WA for a net ionic reaction (A WA holds onto H⁺).

Do separate SB ions. (SBs are soluble ionic compounds.)

What is the volume of NaOH at the equivalence point if 50.0 mL of 0.100 M HCl is titrated by 0.200 M NaOH. ?

• 25.0 mL

• 50.0 mL

• 1.00x10² mL

• 75.0 mL

Answer explanation

Write the neutralization reaction 1st to see the mole to mole ratio for the acid and base.

Tags

NGSS.HS-PS1-7

When HCOOH(aq) is titrated by RbOH(aq), what is the pH at the equivalence point and why does this occur?

• pH > 7 because there is excess NaOH.

• pH < 7 because an acidic salt forms.

• pH = 7 because a neutral salt forms.

• pH > 7 because a basic salt forms.

Answer explanation

What type of compounds are these? Is the salt formed acidic, basic or neutral?

What is the primary hydrolysis reaction at the equivalence point when HF(aq) is titrated by NaOH(aq)?

• HF + NaOH --> NaF + H₂O(l)

• F^-(aq) + H₂O(l) --> HF(aq) + OH^-(aq)

• HF(aq) + H₂O(l) --> F^-(aq) + H₃O⁺(aq)

• Na⁺(aq) + H₂O(l) --> NaOH + H⁺(aq)

Answer explanation

At the equivalence pt, all that remains is a basic salt and water. The basic ion reacts with water.

Which point on the titration curve corresponds to the point at which the moles of the added strong base are equal to the moles of the weak acid initially present? (The points from lowest pH to highest are P, Q, R, S and T)

• Q

• R

• S

• T

Answer explanation

The moles of weak acid = moles of SB added at the equivalence point.

Which acid base pair produced this titration curve?

• HCI + KOH

• HCI + NH₃

• CH₃COOH + KOH

• CH₃COOH + NH₃

Answer explanation

Look at the shape of the curve and how the pH changes to predict this.

Which type of titration is shown by this titration curve?

• Titration of a strong acid by a strong base 

• Titration of a weak acid by a strong base 

• Titration of a strong base by a strong acid 

• Titration of a weak base by a strong acid

Answer explanation

Look at the change in pH and the pH at the equivalence point to select the best response.

Which curve is produced by the addition of a strong acid to a strong base?

• A

• B

• C

• D

Answer explanation

Predict the change in pH for this mixture. Which solution is initially in the flask?

Tags

NGSS.HS-PS1-2