Unit 2 - Acids & Bases Flashcards

Question

Calculations that involve strong acids or bases

Answer 1

You will recall that when a strong acid dissociates in water, the concentration of H3O+ is equal to the concentration of the strong acid. Also, when a strong base dissociates in water, the concentration of OH- is equal to the concentration of the strong base. You must therefore first determine that you are working with a strong acid or base If you know the concentration of a solution, you can calculate the concentrations of the dissociated or ionized species using the mole ratio.

Answer 2

- The self-ionization of water produces a system at equilibrium for which we can write an equilibrium constant for water, Kw. - Kw will be a very small value. This means that the left side of the equilibrium is highly favored. However, we can tell that this equilibrium does in fact exist because pure water will conduct electricity to a very small degree.

Answer 3

Water + water hydronium + hydroxide - This equation represents the auto-ionization of water - the formation of ions by a molecular substance without the addition of another substance. - Since the products of the reaction are hydronium and hydroxide ions, the equation shows that water is an amphoteric substance (i.e., can act as either an acid or a base)

Answer 4

1.0 x 10-7 mol/l. (Therefore, the concentration of hydroxide ions in the same solution must also be 1.0 x 10-7 mol/l). At 25 degrees celsius

Answer 5

Kw, the product of the concentrations of the hydronium ions and the hydroxide ions in water, is called the ion-product constant for water

Answer 6

(H3O+)(OH-) = (1.0 x 10-7) = (1.0 x 10-14)

Answer 7

the concentration of the dissolved acid. Consider [H3O+] in a solution of 0.1 mol/L hydrochloric acid - all the HCl molecules will dissociate in water forming a [H3O+] = 0.1 M - the increased [H3O+] pushes the dissociation reaction between water molecules to the left (Le Chatlier’s Principle) - therefore the [H3O+] that results from the dissociation of water is even less than 1 x 10-7 M. This concentration is negligible compared with the 0.1 M concentration of the HCl

Answer 8

In an acidic solution, [H3O+] is greater than 1.0 x 10-7 M and [OH-] is less than 1.0 x 10-7 M In a neutral solution, both [H3O+] and [OH-] are equal to 1.0 x 10-7 M In a basic solution, [H3O+] is less than 1.0 x 10-7 M and [OH-] is greater than 1.0 x 10-7 M You can use the ion product constant for water, Kw, to determine the concentration of H3O+ or OH- when the concentration of the other ion is known.

Answer 9

You know that nitric acid is a strong acid and barium hydroxide is a strong base. Since both dissociate completely in aqueous solutions, you can use their molar concentrations to determine [H3O+] and [OH-], respectively. You can find the concentration of the other ion using Kw. Note: For a solution of a strong acid,as in H3O+ should be greater than 1.0x10-14 and [OH-] should be less than 1.0 x 10-14 . For a solution of a strong base, [OH-] should be greater than 1.0 x 10-14 and [H3O+] should be less than 1.0 x 10-14 .

Answer 10

The concentration of hydronium ions ranges from about 10 M for a concentrated strong acid to about 10-15 M for a concentrated strong base. - this wide range of concentrations, and the negative powers of 10, are not very convenient to work with - in 1909, a Danish biochemist named Soren Sorensen suggested a method for converting concentrations to positive numbers; this involved the use of logarithms - values that represent the concentrations of hydronium and hydroxide ions in a solution - base 10 logarithms (exponents whose base is 10)

Answer 11

the logarithm of a number is the power to which you must raise 10 to equal that number e.g., the logarithm of 10 is 1 because 101 = 10 the logarithm of 100 is 2 because 102 = 100

Answer 12

pH = -log [H3O+]

Answer 13

- used to compress values that range over several orders of magnitude - pH scale and the Richter scale are both logarithmic scales

Answer 14

- developed by Soren Sorenson in early 1900s to provide a convenient way of showing different levels of acidity and alkalinity.

Answer 15

- at low pH, the concentration of hydronium is high and the concentration of hydroxide is low - as pH increases, hydronium ion concentration decreases and hydroxide ion concentration increases - this relationship is closely related to Kw (more later)

Answer 16

Count only the digits to the right of the decimal point

Answer 17

- the process of decreasing the concentration of a solution

Answer 18

The strength of an acid, or base, is a function of the extent of its reaction with water. The concentration of a solution is a function of the number of moles of solute dissolved per unit of solvent.

Answer 19

- refer to how much of an acid or base is dissolved, to the number of moles of the acid or base in a given volume

Answer 20

- refer to the extent of ionization of the acid or base, indicate how many of the molecules dissociate into ions

Answer 21

- pH meter. Operates on the principle of relative conductivities of solutions - pH paper, pH indicators. Rely on chemical reactions involving special pigments that result in distinctive color changes

Answer 22

A mixture if a weak conjugate acid-base pair that maintains a relatively constant pH when moderate amounts of acid or base are added to it.

Answer 23

- The number of moles of strong acid (H3O+ ) or strong base (OH-) that the buffer can absorb before the ratio of weak acid to conjugate base (or weak base to conjugate acid) differs by more than a factor of 10 - since a buffer may contain different concentrations of its 2 components, its ability to absorb hydroxide will differ from its ability to absorb hydronium - when the ratio of the concentration of the buffer components is close to 1, the buffer capacity is at its maximum - also influenced by the amount of a buffer used - 100 mL of a buffer has 2x the buffering capacity of 50 mL - higher concentrations of the 2 components of a buffer mixture will increase its buffering capacity (i.e., a more concentrated buffer resists pH changes more than a dilute buffer).

Answer 24

- a dramatic change in pH is observed in an unbuffered solution immediately upon the addition of a strong acid or a strong base - for example, a neutral solution of saline whose initial pH is 7.0 will have a pH of 2.0 after the addition of 1 mL of 10 M HCl. S however, blood plasma, whose initial pH is 7.4, will have a pH of 7.2 after the addition of the same amount of HCl

Answer 25

We rely on the carbonic acid/hydrogen carbonate ion buffer to keep our blood plasma at a stable pH of 7.4. A change of more than 0.4 units of pH can cause death. Actually, arterial blood has a pH of 7.4; venous blood pH is slightly lower due to the acidifying effect of higher carbon dioxide concentration.