Buffer Solutions and pH Calculations

[CH3COOH] = 0.100 M, [CH3COO-] = 0.100 M, [H3O+] ≈ 0

The change in concentration of CH3COOH is negative because it is being consumed in the reaction. The change in concentration of CH3COO− is positive because it is being produced in the reaction.

The initial concentration of H3O+ is approximately 0 because the buffer solution is prepared from a weak acid and its conjugate base. The weak acid will only partially dissociate, resulting in a very low concentration of H3O+.

<p>Ka = [H3O+][CH3COO-]/[CH3COOH]</p> Signup and view all the answers

<p>The value of Ka determines the equilibrium concentrations of CH3COOH, CH3COO-, and H3O+ in the buffer solution. The concentration of H3O+ can be determined using the equilibrium constant expression. The pH of the buffer solution is then calculated using the formula pH = -log[H3O+].</p> Signup and view all the answers

<p>The approximation is valid because the dissociation of weak acids is limited, leading to small values of x. This allows us to simplify the equilibrium concentrations to their initial concentrations.</p> Signup and view all the answers

<p>Checking the validity of the approximation ensures that the calculated value of pH is accurate. If the approximation is not valid, then a more accurate calculation must be performed, which may involve the use of the quadratic formula.</p> Signup and view all the answers

<p>pH = -log[H3O+]</p> Signup and view all the answers

<p>Buffer solutions resist changes in pH by neutralizing the added acid or base. This is achieved through the presence of a weak acid and its conjugate base (or a weak base and its conjugate acid). The weak acid/base reacts with any added base/acid, shifting the equilibrium to minimize changes in hydrogen ion (H+) concentration and thus maintain the pH.</p> Signup and view all the answers

<p>The common ion effect occurs when adding a salt containing the conjugate base of the weak acid to the buffer solution, increasing the concentration of the conjugate base. This shifts the equilibrium of the weak acid/base reaction to the left, suppressing the ionization of the weak acid and resulting in a higher pH.</p> Signup and view all the answers

<p>When a base (OH-) is added to a buffer, it reacts with the weak acid (HA) in the equilibrium, forming the conjugate base (A-) and water. This causes the equilibrium to shift to the right, consuming the added OH- and minimizing the pH change. When an acid (H3O+) is added, it reacts with the conjugate base (A-) in the equilibrium, reforming the weak acid (HA) and water, shifting the equilibrium to the left. This neutralizes the H3O+ and prevents the pH from decreasing significantly.</p> Signup and view all the answers

<p>The solution acts as a buffer because it contains appreciable amounts of both the weak acid (acetic acid) and its conjugate base (acetate ion, from sodium acetate). This allows it to neutralize added acid or base by shifting the equilibrium of the acetic acid dissociation reaction to counteract the added stress and keep the pH relatively stable.</p> Signup and view all the answers

<p>Adding a small amount of strong acid to a buffer solution will cause a small decrease in pH, but the change will be much less drastic than if the same amount of acid were added to pure water. This is because the buffer will react with the added acid, neutralizing it and minimizing the change in H+ concentration. In pure water, the addition of acid will significantly increase the H+ concentration, leading to a substantial reduction in pH.</p> Signup and view all the answers

<p>To prepare a buffer with a pH of 4.5 using a weak acid with a pKa of 4.0, you would need to adjust the ratio of the weak acid to its conjugate base. Since the desired pH is slightly higher than the pKa, you would need a slightly higher concentration of the conjugate base than the weak acid. This could be achieved by adding a salt containing the conjugate base to the solution. Maintaining a pH of 4.5 might be needed for various reasons, including optimizing the activity of certain enzymes, ensuring stability of a chemical reaction, or controlling the solubility of a compound.</p> Signup and view all the answers

<p>A buffer solution becomes less effective as the concentration of the weak acid or its conjugate base decreases because it has a lower capacity to neutralize added acid or base. With fewer molecules of the weak acid and its conjugate base available, the equilibrium shifts less effectively to counteract the added stress. This results in a greater change in pH with the addition of the same amount of acid or base.</p> Signup and view all the answers

<p>The pKa of a weak acid is the pH at which the concentrations of the weak acid and its conjugate base are equal. When the pH of a buffer solution is close to the pKa of the weak acid, the buffer is most effective at resisting changes in pH. This is because a small change in pH will only slightly shift the equilibrium between the weak acid and its conjugate base. However, when the pH of the buffer is significantly different from the pKa, the buffer becomes less effective because the equilibrium is more heavily shifted towards one form or the other, making it less able to neutralize added acid or base.</p> Signup and view all the answers

<p>A buffer solution resists changes in pH when acids or bases are added.</p> Signup and view all the answers

<p>The Henderson-Hasselbalch equation allows for the calculation of pH in basic buffers by relating the concentrations of the weak base and its conjugate acid.</p> Signup and view all the answers

<p>To calculate the pKa, use the relationship: pKa + pKb = 14.</p> Signup and view all the answers

<p>A basic buffer system consists of a weak base and a soluble salt of its conjugate acid.</p> Signup and view all the answers

<p>In the equation, [B] represents the concentration of the weak base and [HB+] represents the concentration of the conjugate acid.</p> Signup and view all the answers

<p>The pH of the buffer may change slightly, but the buffer resists significant changes.</p> Signup and view all the answers

<p>'X is small' approximation suggests that the changes in concentration due to the addition of acid or base are negligible compared to initial concentrations.</p> Signup and view all the answers

<p>Weak acids and bases provide a mechanism for reversible reactions that can adjust the pH without allowing drastic changes.</p> Signup and view all the answers

<p>The pH is approximately 4.76.</p> Signup and view all the answers

<p>The 'x is small' approximation allows for the simplification of the equilibrium expressions by assuming that the change in concentrations is negligible.</p> Signup and view all the answers

<p>pKa can be calculated using the formula pKa = -log(Ka).</p> Signup and view all the answers

<p>The pH is approximately 4.19.</p> Signup and view all the answers

<p>Both acid and salt concentrations should be over 100x to 1000x larger than the value of Ka.</p> Signup and view all the answers

<p>The initial values are the concentrations of the weak acid [HA] and its conjugate base [A−].</p> Signup and view all the answers

<p>Ka represents the acidity constant of the weak acid, indicating its strength in dissociating into ions.</p> Signup and view all the answers

<p>The Henderson-Hasselbalch equation simplifies the process of calculating the pH of a buffer solution based on its components.</p> Signup and view all the answers

<p>Perform a stoichiometric calculation for the reaction between the added acid and the buffer's base component.</p> Signup and view all the answers

<p>Adding a base causes it to react with the acid component of the buffer, increasing the concentration of the base component.</p> Signup and view all the answers

<p>Buffer capacity refers to the amount of acid or base that can be added to a buffer without causing a significant change in pH.</p> Signup and view all the answers

<p>The pKa value should be closest to the desired pH of the buffer to ensure effective buffering.</p> Signup and view all the answers

<p>In buffers for added acid, the concentration of [base] should be greater than that of [acid].</p> Signup and view all the answers

<p>A buffer is effective when its pH falls within the range defined by the pKa of the acid and the buffer's effective limits.</p> Signup and view all the answers

<p>The required ratio can be calculated using the Henderson-Hasselbalch equation, which gives approximately 2.3:1.</p> Signup and view all the answers

<p>Formic acid (HCHO2) with pKa 3.74 is the best choice for a buffer at pH 4.25.</p> Signup and view all the answers

A phenomenon where the solubility of a salt is reduced due to the presence of a common ion.

A solution that resists changes in pH upon the addition of small amounts of acid or base.

An equation used to calculate the pH of a buffer from the pKa and concentrations of acid/base.

The negative logarithm of the acid dissociation constant (Ka), indicating the strength of an acid.

The concentrations of acid and conjugate base before any reaction occurs.

The concentrations of species in a solution when the system has reached balance and no net change occurs.

Assumption that changes in concentrations (x) are negligible compared to initial concentrations in equilibrium calculations.

Process of determining the pH level of a buffer solution using its components and the Henderson-Hasselbalch equation.

A principle stating that a system in equilibrium will adjust to counteract changes.

The balance between weak acids and their conjugate bases in solution.

Buffers neutralize added bases by reacting with weak acid molecules.

Buffers neutralize added acids using the conjugate base anion.

The ability of a buffer to maintain pH during acid/base addition.

An table used to track Initial, Change, and Equilibrium concentrations in reactions.

Determining new pH after adding acid or base requires stoichiometry & equilibrium calculations.

The amount of acid or base a buffer can absorb without a significant pH change.

The optimal pH range in which a buffer can effectively neutralize acids or bases.

Select an acid with a pKa closest to the desired buffer pH for optimal buffering.

When acid is added, it reacts with the base component in the buffer to form more weak acid.

When base is introduced, it reacts with the weak acid component to form more base component.

A measure of the strength of an acid in solution, indicating its ability to donate protons.

Represents the concentration of hydronium ions in a solution, determining its acidity.

A numeric scale used to specify the acidity or basicity of an aqueous solution.

The adjustments in the concentrations of reactants and products when equilibrium is reached.

Checking if the assumptions made in calculations are reasonable, especially x's size.

Inserting values for variables into equations to solve for unknowns.

A solution made from a weak base and its conjugate acid.

A substance that partially ionizes in solution to accept protons.

Species formed when a weak base gains a proton.

The pKa of an acid plus the pKb of its conjugate base equals 14.

Assuming initial concentrations equal equilibrium concentrations for buffers.

Buffers resist but can still change pH when acids or bases are added.