Acid Base Equilibria Flashcards

Describe an acidic buffer solution.

An acidic buffer solution is made from a weak acid and a salt of that weak acid.
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Describe an acidic buffer solution.	An acidic buffer solution is made from a weak acid and a salt of that weak acid.
How do buffer solutions work?	In a buffer solution, there is a higher concentration of the salt ion than in the pure acid or base. This allows the ratio of the conjugate acid/base to stay constant, keeping the pH fairly constant.
What happens when small amounts of acid are added to a buffer solution?	The equilibrium will shift to the left, removing nearly all the H+ ions added, due to the high concentration of the salt ion in the buffer.
What happens when small amounts of alkali are added to a buffer solution?	The OH- ions will react with H+ ions to form water, causing the equilibrium to shift to the right and produce more H+ ions.
Describe the process of calculating the pH of buffer solutions.	The pH of buffer solutions can be calculated using the weak acid dissociation expression and considering the initial concentration of the acid and salt. The salt content can be added through a salt solution or by partially neutralizing a weak acid with alkali.
What is the purpose of assuming the [A-] concentration in buffer solutions?	Assuming the [A-] concentration allows us to rearrange the weak acid dissociation expression and calculate the pH of the buffer solution.
Define a buffer solution.	A buffer solution is a solution that resists changes in pH when small amounts of acid or base are added to it. It is made by combining a weak acid and its conjugate base or a weak base and its conjugate acid.
How can a buffer solution be made by adding a solid salt?	A buffer solution can be made by adding a solid salt, such as sodium ethanoate, to a solution of a weak acid, such as ethanoic acid. The salt dissociates to provide the conjugate base, which helps maintain the pH of the solution.
Describe the process of making a buffer solution by adding sodium hydroxide to partially neutralize a weak acid.	To make a buffer solution by adding sodium hydroxide, the weak acid is partially neutralized by reacting it with sodium hydroxide. The moles of the weak acid in excess and the moles of the conjugate base formed are used to calculate the pH of the resulting buffer solution.
Describe the process of calculating change in pH of a buffer on addition of a small amount of acid or alkali.	When a small amount of alkali is added to a buffer, the moles of the buffer acid decrease by the number of moles of alkali added, while the moles of salt increase by the same amount. The pH can then be recalculated with the new values. The same principle applies when a small amount of acid is added, but in this case, the moles of the buffer salt decrease and the moles of buffer acid increase.
How can the pH of a buffer solution be calculated after the addition of a small amount of NaOH?	The moles of acid and salt in the buffer solution before and after the addition of NaOH are determined. The moles of acid decrease by the amount of NaOH added, while the moles of salt increase. The pH can then be calculated using the new values.
What happens to the pH a buffer solution when it is diluted with water?	Diluting a buffer solution with water does not change its pH. This is because the ratio of [HA]/[A-] in the buffer equation remains constant as both the concentrations of salt and acid are diluted by the same proportion.
Describe the process of constructing a pH curve.	Transfer 25cm³ of acid to a conical flask with a volumetric pipette. Measure the initial pH of the acid with a pH meter. Add alkali in small amounts, stirring the mixture to equalize the pH. Measure and record the pH. Repeat the process with smaller volumes of alkali when approaching the endpoint.
What is the purpose of calibrating a pH meter?	Calibrating a pH meter is necessary because pH meters can lose accuracy on storage.
Define the equivalence point in a titration curve.	The equivalence point in a titration curve is the point at which the stoichiometrically equivalent amounts of acid and base have reacted.
Describe the general shape of a titration curve for a weak acid and a strong base.	At the start, the pH rises quickly and then levels off. The flattened part is called the buffer region and is formed because a buffer solution is made.
How can the accuracy of pH probes be improved?	The accuracy of pH probes can be improved by maintaining a constant temperature.
Describe the difference between a weak acid and a weak base.	A weak acid is an acid that does not completely dissociate in water, while a weak base is a base that does not completely ionize in water.
Define pH.	pH is a measure of the acidity or alkalinity of a solution. It is a logarithmic scale that ranges from 0 to 14, with 7 being neutral, values below 7 indicating acidity, and values above 7 indicating alkalinity.
What is the purpose of choosing an indicator in a titration?	The purpose of choosing an indicator in a titration is to visually determine the endpoint of the reaction, which is when the color of the indicator changes and indicates that the reaction is complete.
How do indicators work in a titration?	Indicators can be considered as weak acids. They have a different color in their acidic form (Hln) compared to their conjugate base form (In). The color change of the indicator corresponds to a specific pH range, allowing for the determination of the endpoint of the titration.
Describe the relationship between pH and the equilibrium of an indicator in an acid solution.	In an acid solution, the presence of H+ ions pushes the equilibrium of the indicator towards the reactants. This results in the indicator having a specific color, known as the acidic color.
Describe how to calculate the concentration of a weak acid given its pH.	To calculate the concentration of a weak acid with a given pH, we can use the K2 expression and the known Ka value. First, we take the negative logarithm of the given pH to find [H+]. Then, we substitute [H+] into the K2 expression and solve for [HA].
Define a Bronsted-Lowry base.	A Bronsted-Lowry base is a substance that can accept a proton.
What is the equation for calculating pH?	pH = - log [H+]
How do you calculate the pH of strong acids?	The concentration of hydrogen ions in a monoprotic strong acid will be the same as the concentration of the acid.
Describe the ionic product for water.	In all aqueous solutions and pure water, the equilibrium H2O (I) H+ (aq) + OH- (aq) occurs.
What is the value of Kw for all aqueous solutions at 25°C?	Kw = 1x10-14 mol2dm-6
What is the pH of pure water at 25°C?	pH = 7
Describe how to calculate the pH of a strong base.	To calculate the pH of a strong base, we need to work out the concentration of the hydroxide ion and assume complete dissociation. Then, we can use the Kw expression to find [H+(aq)]. Finally, we take the negative logarithm of [H+(aq)] to obtain the pH value.
Define complete dissociation for strong bases.	Complete dissociation refers to the process in which strong bases completely break apart into their ions when dissolved in water.
Describe the dissociation expression for weak acids.	The dissociation expression for weak acids can be represented as HA (aq) -> H+ (aq) + A- (aq), where HA is the undissociated acid and H+ and A- are the dissociated ions.
What is the pKa value and how is it related to Ka?	The pKa value is the negative logarithm of the Ka value. It is used to express the acidity of a weak acid. The larger the pKa value, the weaker the acid.
How can the pH of a weak acid be calculated?	To calculate the pH of a weak acid, we can make two assumptions: 1) [H+] is equal to the concentration of the dissociated ions [H+(aa)] and 2) the initial concentration of the undissociated acid [HA] remains constant. Then, we can use the K2 expression and take the negative logarithm of [H+] to find the pH value.
Describe the Bronsted-Lowry definition of acid.	A Bronsted-Lowry acid is a substance that can donate a proton.
Describe pH calculations involving neutralisation reactions.	pH calculations involving neutralisation reactions can be complex, especially when determining the pH of a partially neutralised acid or a solution with excess alkali. The method used depends on whether the acid is strong or weak in the partially neutralised case.
Define strong acid and strong base neutralisations.	Strong acid and strong base neutralisations involve the reaction between a strong acid and a strong base to form water and a salt. The pH of the resulting mixture can be calculated by determining the concentration of excess H+ or OH- ions.
How do you calculate the new concentration of excess H+ ions in a strong acid and strong base neutralisation?	To calculate the new concentration of excess H+ ions in a strong acid and strong base neutralisation, divide the moles of excess H+ ions by the total volume of the solution (in dm³).
Describe the process of determining which ion is in excess in a strong acid and strong base neutralisation.	To determine which ion is in excess in a strong acid and strong base neutralisation, calculate the concentration of excess H+ and OH- ions separately. The ion with the higher concentration is the one in excess.
Do strong diprotic acids and bases affect pH calculations differently?	Yes, strong diprotic acids and bases, such as H2SO4 and Ba(OH)2, can affect pH calculations differently. The number of moles of H+ or OH- ions produced will be twice the number of moles of the diprotic acid or base used.
Describe the process of calculating the new concentration of excess HA in a weak acid and strong base neutralization.	The new concentration of excess HA can be calculated by subtracting the moles of OH- from the initial moles of HA and dividing by the total volume.
What is the formula to calculate the concentration of salt formed [A-] in a weak acid and strong base neutralization?	The concentration of salt formed [A-] can be calculated by dividing the moles of OH- added by the total volume.
Define pH and how it is calculated in a weak acid and strong base neutralization.	pH is a measure of the acidity or alkalinity of a solution. In a weak acid and strong base neutralization, pH can be calculated using the formula pH = -log[H+].
Describe the process of calculating the pH of a resulting mixture in a specific example of weak acid and strong base neutralization.	In the given example, the pH of the resulting mixture can be calculated by rearranging the equation Ka=[H+][A-] to get [H+], and then substituting the values to find the pH.
How can the pH of a weak acid at half equivalence be simplified?	At half equivalence, the assumption can be made that [HA] = [A-]. Therefore, [H+(aq)] = K2 and pH = pKa.
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