Download Buffer Solutions and pH Maintenance and more Exams Chemistry in PDF only on Docsity!
Buffer - correct answer ✅Something that minimizes impact of the external force (in acid-base systems, force = pH) Acid-Base Buffer - correct answer ✅A solution that will minimize changes in pH upon the addition of acid or base What is a buffer made of? - correct answer ✅An acidic and a basic component - a conjugate acid-base pair (weak acid and conjugate base or weak base and conjugate acid) How do buffers work? - correct answer ✅Through the common ion effect Common Ion Effect - correct answer ✅Occurs when a given ion is added to an equilibrium mixture that already contains that ion, and the position of equilibrium shifts away from forming it What does adding a common ion do? - correct answer ✅It decreases the percent dissociation of the acid and therefore increases the pH, making the solution less acidid Buffer Components - correct answer ✅Large quantities of acid and its conjugate base that consume small quantities of acid or base by shifting equilibrium, and therefore adjusting pH only slightly
What happens to a buffer when a small amount of strong acid or strong base are added to it? - correct answer ✅The pH changes very slightly Henderson-Hasselbach Equation - correct answer ✅pH = pKa + log([base]/[acid]) Buffer Characteristics - correct answer ✅1. Buffer Capacity
- Buffer Range Buffer Capacity - correct answer ✅Strength of the buffer, ability to maintain pH after the addition of acid or base - depends on absolute and relative concentrations of components Absolute Concentration - correct answer ✅The higher the concentration of the buffer, the higher the capacity Relative Concentration - correct answer ✅The closer the concentrations of the buffer components are to each other, the greater the capacity
greater than the amount of H3O+ or OH- added
- The buffer-component concentration ratio determines the pH; the ratio and the pH are related by HH equation Titration - correct answer ✅A laboratory exercise helping understand acid-base properties, but the titration curve can also help provide information about buffer Acid-Base Indicator - correct answer ✅Typically a weak acid (Hln) which will have a different color compared to its conjugate base (ln-) If [Hln]/[ln-] is 10/1 or bigger - correct answer ✅You will see the color of Hln If [Hln]/[ln-] is 1/10 or smaller - correct answer ✅You will see the color of ln- Equivalence Point of a Titration (strong acid/base) - correct answer ✅Occurs when the number of moles of added OH- equals the number of moles of H3O+ originally present
End Point of a Titration (strong acid/base) - correct answer ✅Occurs when the indicator, which was added before the titration, changes color. Indicator is chosen with a color change close to the pH of the equivalence point - the visible end point signals the invisible equivalence point Types of Titration Curves - correct answer ✅1. Strong Acid-Strong Base
- Weak Acid-Strong Base
- Weak Base-Strong Acid
- Polyprotic Acid Strong Acid-Strong Base Curve Features - correct answer ✅1. Curve starts at a low initial pH (it is a strong acid being titrated with a strong base)
- pH rise happens gradually - pH jump between 6 and 8
- Slow increase after jump
- Equivalence point = +/- 7.
- End Point What does a strong base-strong acid titration look like? - correct answer ✅The opposite of a strong acid-strong base titration because now a strong acid is being added to a strong base so initial pH is high
- Multiple buffer regions and equivalence points
- pH of midpoint of buffer region is the pKa of the acid
- Second pKa is higher than 7 because formed species can act as a base Amino Acids - correct answer ✅Contain a weak base and a weak acid, act as a polyprotic acid, exist in charged forms that depend on the pH of the solution and determine the overall charge of a protein, which can affect a protein's function Summary of Section 19.2 - correct answer ✅1. Acid-base indicator is a weak acid that has a different colored conjugate base
- Strong acid/strong base titration starts at a low pH, rises slowly, then shoots up near eq. point (7)
- Weak acid/strong base titration pH starts higher, rises slowly in the buffer region, then rises quickly near eq. point (greater than 7)
- Weak base/strong acid titration curve has an inverse shape of the weak acid/strong base titration, the pH decreasing to the eq point (less than 7)
- Polyprotic acids have 2 or more acidic protons
- Amino acids exist in charged forms that depend on the pH of the solution and determine the overall charge of a protein, which can affect a protein's function Ionic Compounds - correct answer ✅A metal cation and a nonmetal anion - for binary ionic compounds, the difference in electronegativity should be more than 2. 2 Groups of Ionic Compounds - correct answer ✅1. Soluble and slightly soluble
- Insoluble Solubility-Product Constant - correct answer ✅Ksp - When a solution becomes saturated, Qc keeps a constant value - it is called Ksp. At a saturated point, the ionic compound will no longer dissociate Ion-Product Expression - correct answer ✅Qsp - For a slightly soluble compound
How can you tell if a precipitate will form? - correct answer ✅Need to compare Qsp and Ksp Qsp = Ksp - correct answer ✅Solution is saturated and no precipitate will form, solution is at equilibrium Qsp > Ksp - correct answer ✅Precipitate will form until the remaining solution reaches saturation Qsp < Ksp - correct answer ✅No precipitate will form since the solution is not saturated, not yet at equilibrium How to Separate Ions - correct answer ✅1. Selective Precipitation
- Simultaneous Equilibria Selective Precipitation - correct answer ✅Precipitating ion is added to the solution until Qsp of the more soluble compound is almost equal to its Ksp, the less soluble compound will precipitate in as large a quantity as possible, leaving behind the ion of the more soluble compound Simultaneous Equilibriua - correct answer ✅Addition of a strong acid - the equilibrium will shift to the left so the less soluble sulfide will precipitate
Addition of a strong base - the equilibrium will shift to the right so more soluble sulfide will precipitate Complex Ion - correct answer ✅Consists of a central metal ion covalently bonded to two or more anions or molecules, called ligands Ligands - correct answer ✅A molecule or anion bonded to a central metal ion in a complex ion What will the addition of a ligand do to the solubility? - correct answer ✅It will increase the solubility of slightly soluble compounds, if that ligand will form a complex ion with a metal cation Amphoteric Hydroxides and Complex Ions - correct answer ✅Can interact with both acids and bases, dissolve in acid and base due to reactions that involve complex ions What happens to the solubility when an acid is added? - correct answer ✅The solubility increases Summary of Section 19.3 - correct answer ✅1. Adding a common ion lowers a compound's solubility
and/or work are absorbed or released - accounts for energy conservation and conversion but not info about direction Enthalpy (H) - correct answer ✅Thermodynamic parameter that is directly related to energy changes at constant pressure, sign of delta H does not predict direction of the reaction ΔH < 0 - correct answer ✅Exothermic process (system is releasing energy) ΔH > 0 - correct answer ✅Endothermic process (system is absorbing energy) Freedom of Motion in States of Matter - correct answer ✅1. Phase change: Solid --> liquid --> gas
- Dissolving a salt: Crystalline solid + liquid --> ions in solution
- Chemical change: Crystalline solid --> gases + ions in solution What is a KEY factor in predicting the direction of spontaneous processes? - correct answer ✅A change in freedom of motion in a system
Microstate - correct answer ✅When looking at a system as a whole the combination of quantized energies is called a microstate and the total energy of the system is spread out through microstate at any point in time What happens to a system with fewer microstates? - correct answer ✅It has a lower entropy What happens to a system with more microstates? - correct answer ✅It has a higher entropy Entropy - correct answer ✅A state function meaning that it depends only on the present state of the system, but not how the system got there - degree of disorder Reversible Process - correct answer ✅Occurs in such tiny increments that the system remains at equilibrium, and the direction of the change can be reversed by microscopic reversal of conditions Second Law of Thermodynamics - correct answer ✅The entropy of an isolated system can only increase over time What happens to the entropy of an isolated system over time? - correct answer ✅It can only increase over time
What happens with entropy when dissolving gas in water? - correct answer ✅Gas already has a pretty high entropy, entropy of a solution of gas in a liquid (solid) is smaller than the entropy of the gas itself Trends in Entropy - correct answer ✅1. Within a group, entropy increases
- For different forms of an element, entropy is higher in the form that allows more freedom of motion
- More complicated the chemical formula of the compound, the higher the entropy Exothermic Reaction - correct answer ✅Heat is released by the system and absorbed by the surroundings (qsys < 0, qsurr > 0, ΔSsurr > 0) Endothermic Reaction - correct answer ✅Heat is absorbed by the system and released by the surroundings (qsys > 0, qsurr < 0, ΔSsurr < 0) What happens with spontaneity when a system reaches equilibrium? - correct answer ✅Neither the forward or the reverse reaction is spontaneous, so no net reaction in either direction
Gibbs Free Energy (G) - correct answer ✅Combines the enthalpy and entropy of a system ΔG < 0 - correct answer ✅Spontaneous Reaction ΔG > 0 - correct answer ✅Non-spontaneous Reaction ΔG = 0 - correct answer ✅Process at equilibrium When is a reaction spontaneous at all temperatures? - correct answer ✅If ΔH < 0 and ΔS > 0 --> ΔG < 0 for all T When is a reaction nonspontaneous at all temperatures? - correct answer ✅If ΔH > 0 and ΔS < 0 --> ΔG > 0 for all T When will a reaction become spontaneous as temperature increases? - correct answer ✅If ΔH > 0 and ΔS > 0 --> ΔG becomes more negative as T increases When will a reaction become spontaneous as temperature decreases? - correct answer ✅If ΔH < 0 and ΔS < 0 --> ΔG becomes more negative as T increases
