Fluent Essays

Name: ________ __ _________________________ CHEM 1212 Module 11 Reading Guide Titrations There are four regions on a titration curve. 1. The initial pH of the solution. pH is found using the concentration of a ____________ acid or base, or the initial concentration and the ____________ for a weak species. 2. The segment of the curve between the initial pH and the ____________ point. For a weak acid, this region is buffering and the center point can be used to find ____________. The Henderson-Hasselbalch equation can be used if the ratio of the ____________ to the weak acid is between 0.10 and 10 and the difference between concentration and Ka is sufficient to make the ‘x is small’ approximation valid. 3. The equivalence point. At this point, sufficient titrant has been added to ____________ with the initial acid or base. 4. The segment of the curve after the equivalence point. pH in this region is calculated using the excess ____________ added. You have to subtract the volume of titrant that reacted up to the ____________ point. The equivalence point of a titration between a ____________ acid and strong base is 7.0 because the salt produced is ____________. The equivalence point of a weak acid or base will not be at 7 because these species do not create the same amount of H+ or OH- as the strong species of the same concentration. In weak acid–strong base titration curves, the weaker the acid, the ____________ the initial pH of the titration. Acids with ____________ Ka values also exhibit a more pronounced initial pH change when base is first added. Weak acids titrated with strong bases display a less abrupt pH change near the equivalence point than ____________ titrated with strong bases. The ____________ the Ka of the acid, the more “elongated” the titration curve. Weak base–strong acid titrations are conceptually similar to the weak acid–strong base titrations. The main difference is that the initial pH is basic and the pH at the equivalence point is acidic. The pH at the half-equivalence point is equal to the pKa of the conjugate acid of the weak base being titrated. The titration curves of ____________ acids are similar in shape to those of monoprotic weak acids, but they contain more than one equivalence point.  ____________ that are used in acid–base titrations produce visible color changes that mark the ____________ point of the titration. An appropriate indicator can be used to show the visible end point of the titration, which is near the ____________ point of the titration. An appropriate indicator for a particular titration must change color over a range that either overlaps with or is close to the ____________ point. Practice Problems For the titration of 25.00 mL of 0.100 M CH3CO2H with 0.100 M NaOH. The reaction can be represented as: CH3CO2H + OH− ⟶ CH3CO2− + H2O (a) What is the initial pH before any amount of the NaOH solution has been added? Ka = 1.8 × 10−5 for CH3CO2H. (b) Find the pH after 12.50 mL of the NaOH solution have been added. (c) Find the pH after 25.00 mL of the NaOH solution has been added. (d) Find the pH after 37.50 mL of the NaOH solution has been added. Precipitation In a ____________ system, species in different phases interact with one another. The ____________, Ksp , of a slightly soluble ionic compound can be related to its measured ____________ provided the dissolution process involves only dissociation and solvation (instead of extra side reactions). The solid compound is conventionally written on the ____________ side of the equilibrium double-arrow and the ____________ are written on the right side. Ksp is equal to the product of that compound’s ion concentrations in a ____________ solution, each raised to the power of its ____________ in the balanced chemical equation. Solids do not appear in equilibrium expressions because their concentrations are considered ____________. Molar solubility is the number of ____________ of a substance that are dissolved in 1 liter of saturated solution. Although the solubility product constant of a compound is related to the solubility of that compound, the two terms are not mathematically equal and should not be used interchangeably. Generally speaking, a ____________ value of Ksp means a lower solubility, just as a small Ka value means a ____________ acid. The situations in which the relative solubility of two compounds can be directly compared by using their Ksp values are restricted to cases where their reaction stoichiometries are ____________. The common-ion effect ____________ the solubility of an ionic compound that is dissolved in a solution containing a common ion. The mathematical product of ion molarities is ____________ in an equilibrium mixture regardless of the source of the ions, so an increase in one ion’s concentration must be balanced by a proportional ____________ in the other. The pH of a solution will affect the ____________ of an ionic compound that has a basic anion, which includes anions that are ____________ bases of weak acids. The addition of another base will ____________ the solubility of these compounds. The solubility of compounds with a neutral anion is not enhanced in ____________ solution. A solute with finite solubility can yield a ____________ solution when it is added to a solvent in an amount exceeding its solubility, resulting in a heterogeneous mixture of the saturated solution and the excess, undissolved solute. The calculation of Q and the comparison of the resulting value to the ____________ of a substance will tell you if a solution is ____________, saturated, or supersaturated. A solution at ____________ has Q = K and is saturated with the ____________ of dissolution and precipitation equal to each other. If Q is greater than K, the solution is supersaturated and will undergo ____________ at a faster rate than dissolution until it reaches ____________. If Q is less than K, the solution is ____________ and no ____________ is observed. More compound will dissolve until the solution is ____________. When several ions are present in a solution, one or more ions can be selectively precipitated and removed from solution based on the different ____________ of the ions. This is true even if the ions forming the insoluble salt come from two different soluble salts that are then mixed together. If you are separating two ions that make insoluble products with a specific counter ion, they will need to have a significant difference in solubility for this to be effective. The ____________ soluble compound will precipitate first. Practice Problems Calculate the molar solubility of Li3PO4, Ksp = 2.37 × 10−11 in pure water. Calculate the molar solubility of Li3PO4, Ksp = 2.37 × 10−11, in a solution containing 8.0 × 10−3 M LiCl. Compare your answer to that found in the previous question. Text segments from Flowers, P. et. al.(n.d.). Precipitation and Dissolution. In Chemistry: Atoms First 2e. org/books/chemistry-atoms-first-2e/pages/15-1-precipitation-and-dissolution ; White, J. et al. Interactive General Chemistry. MacMillan, NY. 2019.; Chemistry LibreTexts, Libretexts, [online] Available from: https://chem.libretexts.org/Ancillary_Materials/Demos_Techniques_and_Experiments/General_Lab_Techniques/Titration/Titration_of_a_Weak_Acid_with_a_Strong_Base Reading guide style Adapted from Ionic equations Study Guide by Montgomery College is licensed under CC BY 4.0 Document not to be reposted on the internet without express permission.