Chemistry Quarter IV Review - Answers Formulas and Possibly Necessary Data Δtf = Kf m Δtb = Kb m m = mol solute / mass solvent(kg) C = n V m = nm - log[h3o + ] = ph - log[oh - ] = poh [H3O + ] = 10 =ph [OH - ] = 10 - poh 14 = poh + ph Kw = [H3O + ][OH - ] Kw = 1.0x10-14 Chapter 13 Review Questions: 1. Write the dissociation equation for the dissolution of the following in water and then determine the number of moles of each ion produced as well as the total number of moles of ions produced. a. 2.5 mol of sodium sulfate H2O Na2SO4(s) - - - - > 2 Na 2+ (aq) + SO4 2- (aq) 2.5 mol 5.0 mol 2.5 mol Total produced: 7.5 mol b. 1.75 mol of strontium hydroxide H2O Sr(OH)2(s) - - - - - - > Sr 2+ (aq) + 2 OH - (aq)
1.75 mol 1.75 mol 3.50 mol Total produced: 5.25 mol 2. What is a nonvolatile substance? Does adding a non- volatile substance to a solvent increase or decrease the boiling point? Increase or decrease the freezing point? Non- volatile substances do not easily change state. As you add a non- volatile substance the freezing point will decrease and the boiling point will increase. 3. What is the new freezing point of a 1.5 m solution of sucrose in water? (Kf = - 1.86C /m) Δtf = Kf m Δtf = (- 1.86 C/m)(1.5m) Δtf = - 2.79 C 4. What concentration of ethylene glycol is needed to raise the boiling point of water to 102 C? (K b = +0.51C /m) Δtb = Kb m (102 C - 100 C) = (0.51 C/m)m (2.0 C) = (0.51 C/m)m 3.92156m = m 3.9m 5. What is the boiling- point elevation of a solution made from 15.0 g of a nonelectrolyte solute and 250.0 g of water? The molar mass of the solute is 50.0 g and K b = 0.51 C/m. n = m/m = (15.0g)/(50.0g) = 0.3 mol m = n/m = 0.3 mol/0.250kg = 1.2m Δtb = Kb m Δtb = (0.51 C/m)(1.2m) Δtb = 0.612 C Δtb =0.61 C Chapter 14 Review Questions (this is your actual chapter 14 review. It will be quite valuable for this exam). 6. Name five characteristics of acids: Page 442 in the textbook. 7. Name five characteristics of bases: Page 445 in the textbook. Strong acids you need to remember: HCl, HI, HBr, H2SO4, HNO3, H2CO3 Weak acids you need to remember: H3PO4, CH3COOH, HF There are two different definitions of acids and bases that we talked about this chapter: 1. Arrhenius acids and bases 2. Bronsted- Lowry acids and bases Arrhenius believed that acids and bases had to be dissolved in water. He also believed that acids released H + (aq) and this would form H3O + (aq) in solution. For bases, he said that OH - (aq) must be released. However, this explanation could not explain acids and bases fully. For example:
- NH3 (ammonia), is a base So is Na2CO3. However, it does not have a OH - (hydroxide) to release. - CH4 would have been predicted to release at least one hydrogen, making an acidic solution. This is not the case when CH4 is added to water. Bronsted- Lowry acids and bases are defined slightly differently: Bronsted- Lowry Acids are proton (hydrogen) donors Bronsted- Lowry Bases are proton (hydrogen) acceptors In Bronsted- Lowry acid and base reactions every acid has a conjugate base pair and every base has a conjugate acid pair. Multiple Choice Type questions: 8. Which of the following is a Bronsted- Lowry base? a. HCl b. HSO4 - because of the negative it can accept a proton c. H3O + d. H3PO4 9. In the following reaction, which of the options is a conjugate acid- base pair? a. H2C2O4(aq) and CH3NH2(aq) b. H2C2O4(aq) and CH3NH3 + (aq) c. CH3NH2(aq) and CH3NH3 + (aq) d. HC2O4 - (aq) and CH3NH3 + (aq) Written Questions: 10. a) H2SO4(aq) is a polyprotic acid (more specifically a diprotic acid). Provide all of the correct equations for the dissociation of sulfuric acid when placed in water. Remember to include all necessary charges and states of matter. H2SO4(aq) + H2O(l) à H3O + (aq) + HSO4 - (aq) HSO4 - (aq) + H2O(l) à H3O + (aq) + SO4 2- (aq) b) Which reaction happens more frequently in real life? The first one or the second one? The first reaction for a polyprotic acid will always happen more readily (often) when compared to the second one.
11. Using your knowledge of Bronsted- Lowry theory, is HSO4 - (aq) an acid, a base, or both? Explain. HSO4 - (aq) is both a Bronsted- Lowry acid and a Bronsted- Lowry base. It contains a proton (hydrogen) that can be donated to create hydronium and the sulfate ion (see question 17). However, it also contains a negative charge, allowing it to accept a proton to create sulfuric acid. Objects that act as both an acid and a base are called (the word starts with an a) Acid Nomenclature: Hydrogen ide à hydro ic acid Hydrogen ate à ic acid Hydrogen ite à ous acid Hydrogen hypo ite à hypo ous acid 12. Complete the following chart for the given acids: Formula Nitric acid HNO3(aq) Name HCN(aq) HClO(aq) Hydrogen nitrite HBr(aq) H3PO4(aq) Hydrocyanic acid Hypochlorous acid Nitrous acid Hydrobromic acid Phosphoric acid 13. What is a binary acid? What is an oxyacid? Give two examples of each. Oxyacid is an acid that is a compound of hydrogen, oxygen, and a third element, usually a nonmetal. (HNO3(aq), CH3COOH(aq)) Binary acids are acids that contain only two different elements: hydrogen and one of the more electronegative elements. (HCl(aq), HF(aq)) Determining Acid Base Strength: 14. What characteristic of an acid or base molecule determines whether or not it will be a strong acid/base or a weak acid/base. (Hint: think dissolving). Strong acids and strong bases dissociate easily. This produces more hydronium or hydroxide than if the molecule does not dissociate easily. 15. Complete the following table. Note: All of the states in the following table are (aq), unless it is water (H2O), then the state will be liquid (l)
Acid Base Con. Acid Con. Base Equation 9 HNO2 H2O H3O + NO2 - HNO2 + H2O- > NO2 - + H3O + 10 H2O F- HF OH- H2O + F - - > HF + OH- 11 NH3 HCN NH4 + CN - NH3 + HCN - > NH4 + + CN - 12 HClO3 OH- H2O ClO3 - HClO3 + OH- - > H2O + ClO3-13 H2O S 2- HS - OH - S 2- + H2O - > OH - + HS - 14 HCO2H OH - H2O CO2H - HCO2H + OH - - > H2O + CO2H - Chapter 15 Review Questions: 23. What is the end point of a titration? The end point of a titration is when the color of the acid base indicator changes. The equivalence point of a titration is when the two substances are present in equivalent amounts. In a perfect situation, the end point and the equivalence point will be the same. 24. Draw an acid base curve for the titration of: Reference the follow link for more information on Acid/Base titration curves: http://www.chemguide.co.uk/physical/acidbaseeqia/phcurves.html a) a strong acid with a weak base b) a strong base with a weak acid c) weak base with a strong acid d) weak acid with a strong base e) strong acid with a strong base f) strong base with a strong acid 25. Complete the following five multiple choice questions: i) What is the [OH- ] of a solution whose ph = 5.43? a. 1.0x10-7 M b. 3.7x10-6 c. 2.7x10-9 M d. 8.57 M ii) In an aqueous solution, [H3O + ][OH- ] =. a. 1.0x10-14 M b. 1.0x10-7 M c. 1.0x10 14 M d. 7.0 M iii) In an acidic solution, which of the following is true? a. [H3O + ] = [OH- ] b. [H3O + ] < [OH- ] c. [H3O + ] < 1.0x10-7 M d. [H3O + ] > [OH- ] iv) Consider a 2.0x10-4 M solution of HCl(aq). What is the [OH- ] concentration of this solution? a. 5.0x10-11 M b. 2.0x10-4 M c. 10.30 M d. 1.0x10-14 M 26. If you would like more practice of these questions, check out the following link: http://www.sciencegeek.net/apchemistry/aptaters/phcalculations.htm