Chemistry 1.7 Acids and Bases & Chemistry 1.8 Titrations

Which of the following acids has the weakest conjugate base? A) HNO3 B) HF C) H2CO3 D) HClO2

A) HNO3

How can you find the pKa on a titration curve?

At half-equivalence point, pH = pKa

47.0g of nitrous acid, HNO2, is added to 4L of water. What is the resulting pH? (Ka = 4.1x10^-4) A) 3.5 B) 2.0 C) 2.5 D) 3.2

B) 2.0

Which of the following pH values is an acceptable equivalence point for a weak base being titrated by a strong acid? A) 7.7 B) 5.2 C) 11.4 D) 7.0

B) 5.2 The equivalence point is the point during a titration when there are equal equivalents of acid and base in the solution. Since a strong acid will have more effect on the pH than the same amount of a weak base, we predict that the solution's pH will be acidic at the equivalence point.

Consider two solutions: solution A and solution B. Solution A is a 0.1M hydrogen iodide solution and solution B is a 0.1M hydrochloric acid solution. What can you conclude about these two solutions? A) Solution B has twice as many hydrogen ions as solution A B) Both solutions have approximately equal amounts of hydrogen ions C) Solution A has twice as many hydrogen ions as solution B D) Both solutions have high pKa values

B) Both solutions have approximately equal amounts of hydrogen ions

Why is BF3 a lewis acid?

Because it accepts a pair of electrons

Why can water be a bronsted-lowry base?

Because it can accept a proton

Why is H2O a lewis base?

Because it can donate a pair of electrons

Why is HCl an Arrhenius acid?

Because it can produce an H+ion in water

Why is NaOH an Arrhenius base?

Because it can produce an OH- in water

Why is HCl a bronsted-lowry acid?

Because it donates a proton

Which of the following describes a Brønsted-Lowry acid? A) A substance that donates an electron pair B) A substance that accepts an electron pair C) A substance that produces hydroxide ions in an aqueous solution D) A substance that donates a proton

D) A substance that donates a proton

__________ the pH of an acidic solution will __________ the pKa of the acid. A) Increasing . . . decrease B) Increasing . . . increase C) Decreasing . . . increase D) Decreasing . . . not change

D) Decreasing . . . not change pKa is a measure of the strength of an acid (meaning how easily it can dissociate into hydrogen ions and its conjugate base). Altering the pH of the solution will have no effect on the strength, and subsequently pKa, of the acid.

Which of the following is true regarding an acid and its pKa? I. One can increase the strength of an acid by decreasing its pKa value II. pKa increases as the acid dissociation constant decreases III. pKa of an acid cannot be changed by altering the concentration of the acid A) I and II B) I and III C) I, II, and III D) II and III

D) II and III pKa=−log(Ka) Ka is a measure of the equilibrium strength of an acid and is unique for each acid. The higher the value of Ka, the stronger the acid; however, a particular acid's Ka value, and subsequently its strength, can never be changed. The only way you can change the Ka of an acid is by changing the identity of the acid itself. This means that the pKa value of an acid is also always constant; therefore, you cannot decrease an acid's pKa. Using the definition of pKa, we can see that the pKa of an acid increases as you decrease the acid dissociation constant (Ka). A strong acid will have a high Ka and a low pKa. The pKa of an acid can never be altered; therefore, changing the concentration of the acid will not alter the pKa of the acid. It might change the amount of hydrogen ions produced and alter the pH; however, the pKa of the acid will stay constant

Which of the following is the strongest acid? A) HBr B) HI C) HCl D) HF

Hydroiodic acid (HI) is the strongest acid listed. Charge density decreases as the atomic size gets larger, thus stabilizing the charge when a hydrogen is given off. Hydroflouric acid (HF) is a relatively weak acid because electronegative elements hold on to their valence electrons more tightly, and are thus less likely to dissociate.

Bronsted-Lowry Base

Proton acceptor (H2O)

Bronsted-Lowry acid

Proton doner (ex: HCl)

A weak acid is slowly titrated with a strong base. Where on the titration curve would the solution be the most well-buffered? A) The half equivalence point B) When the amount of base added equals the amount of acid in the solution. C) When no base has been added D) The equivalence point

The half equivalence point Explanation: At the half equivalence point, the concentration of acid in the solution is equal to the concentration of the conjugate base in solution. At this point, the graph shows a line that is near horizontal. This means that base or acid could be added and the pH of the solution would change very slowly.