Chem Discussion #8 Chapter 6 and 7 KEY

Transcription

1 Chem Discussion #8 Chapter 6 and 7 KEY Things you should know when you leave Discussion today: Acid Base Reactions xidation Reduction Reactions xidation is loss of electrons (acts as a reducing agent) Reduction is gain of electrons (acts as a oxidizing agent) 1. Balance and Answer the following about the oxidation reduction reaction given below Half Reaction: Zn(s) Zn + (aq) +e Zn(s) + Cu + (aq) Zn + (aq)+ Cu(s) Identify if your half reaction is oxidation: Half Reaction: Cu + (aq) + e Cu(s) Identify if your half reaction is reduction: xidized Reactant: Zn(s) Reduced Reactant: Cu + (aq) xidizing Agent: Cu + (aq) Reducing Agent: Zn(s) How many es of the electrons are transferred per e of reaction? s. Complete the following reaction: Cu(s) + Fe + Fe(s) + Cu + a) How many es of the electrons are transferred per e of reaction? 6 s. Give a definition and an example for BrønstedLowry acid: proton donor. Give a definition and an example for Lewis base: Lewis base provides electron pair so the bond can form

2 5. Ammonia, NH, is a useful household cleaner, fertilizer, and antimicrobial compound. a) If NH acts as an acid in water, write the balanced chemical equation. Label the BrønstedLowry acid and its conjugates. NH (aq) + H (l) NH (aq) + H + (aq) b) If NH acts as a base in water, write the balanced chemical equation. Label the BrønstedLowry acid and its conjugates. NH (aq) + H (l) NH + (aq) + H (aq) c) A small amount of aluminum nitrate is added to the products of the acid/base reaction in (b) and a precipitate forms. Write the balanced, netionic equation for the precipitation. Al + (aq) + H (aq)al(h) (s) d) Ammonia is the conjugate acid in the reaction of the strong base amide, NH with water. Write the acid/base reaction of amide, NH, with water and label the BrønstedLowry acid reactant in this reaction. NH (aq) + H (l) NH (aq) + H (aq) 6. Consider the four acid/base reactions below. In the reaction NH(aq) + HC(aq) NH + (aq) + HC (aq ) the conjugate base is HC In the reaction CHC (aq) + H(l) CHCH(aq) + H (aq), the conjugate acid is CH CH. In the reaction Fe + (aq) + 6 H(l) [Fe(H)6] + (aq), the Lewis acid is Fe +. No conjugates Lewis base is H : 7. List all strong acids you know. Why do we call them strong? HCl, HBr, HI, HN, H S, HCl HCl, HBr, HI, HN, H S, HCl a) How many hydronium ions are in 1.5L of 0.0M solution of HCl? HCl N H ions Cl L A ions

3 8. The 0.10 e of sulfuric acid in 50.0 ml of water produces the concentration of the hydronium ion to be.5 M. If you know that sulfuric acid is a strong acid and consider that acids always donate one proton at a time according to the following reactions: H S (aq)+ H (l) H + (aq) + HS (aq) HS (aq) + H (l) H + (aq) + S (aq) Is HS acting as a strong acid or a weak acid? Prove your answer..5h.5 M H + = ; total number of es of H + (aq) is:.5h 50.0mL 0. 15s 0. S From the first reaction: 0. = 0.1 HS (aq) S From the second reaction:.s 0.1MH S 0 If both acids reacted as a strong acid we will have 0.s of H + (aq) but from the concentration we can see.5h that we only have 50.0mL 0. 15s. That means that HS is a strong acid because it does not react 100% Different approach: 0. S H S.00MH S =.00M [HS ] 0.050L.00H S From first reaction assuming H S (aq) is a strong acid: S.00MH From the second reaction assuming HS is a strong acid :.00HS S.00MH Total concentration of H + will be M if both acids act as strong acids. That means that HS is a strong acid because it does not react 100%

4 9. I add 5.00 es of solid NaN to 500. ml of a 1.00 M Pb(N ) solution, which does not change the volume. I then pour in 500. ml of hydrochloric acid that is M. I let the solution come to equilibrium. (Remember that nitric acid and hydrochloric acid are both strong acids) +500mLof MHCl HCL L 0.5HCl 0.5Cl 0.5H 5.00 N 5.00 Na Pb N Initially 500mL 6.00 N 0.5H 0.75 Pb + Final a. What is the final ar concentration of H + ion in solution?(answer:0.5m) 0.5HCL Cl 0.500L 0.5HCl 0. 5H ; [ b. What is final ar concentration of Cl ion? [Cl]= 0M ; [Pb + ]= 0.75M Pb + (aq) + Cl (aq) PbCl (s) H ]=0.5/=0.5M Pb + (aq) + Cl (aq) PbCl (s) All of it ppt [Cl]= 0M (LR) 1Pb 0.5CL 0.15Pb used Cl left 0 left c. [Pb + ]= 0.75M d. What is the final ar concentration of the nitrate ion??(answer: 6.00M) 10. When the two compounds below are mixed, circle the one that behaves as a Lewis base a) H :(LB) NH + (LA) b) :NH (LB) H (LA) c) C (LB) H (LA) d) BF :NH (LB) 11. Give an example of neutralization reaction: NH (aq) + HCl(l) NH (aq) + H (l)

5 1. We are going to cool 8g of water from 10. C down to 0.0 C (specific heat of water is. J/(K g)). During this process of cooling what is true? a. Heat is absorbed by the water or Heat is released by the water (choose one) b. q system< 0, q system> 0, q system= 0 (choose one) c. q surroundings < 0, q surroundings> 0, q surroundings= 0 (choose one) d. What is q system in Joules? (Answer:1.kJ) e. What is q surroundings Joules? q surroundings=mc T=1.kJ 1. Define enthalpy of fusion Δ fush : energy needed when 1 of solid is transferred into 1 liquid 1. We are going to freeze 8g of water at 0.0 C down to 0.0 C ice (Δ fush= 6.00 kj/; melting). During this process circle all that apply: a) There is a net gain in the number of Hbonds or There is a net loss in the number of Hbonds b) Heat is absorbed by the water or Heat is released by the water c) Process is exothermic or Process is endothermic d) q system< 0, q system> 0, q system= 0 (choose one) e) q surroundings < 0, q surroundings> 0, q surroundings= 0 (choose one) f) What is a temperature change of the system? no T change 1 ( 6.00kJ) g) Calculate q system in Joules??(Answer:9.kJ) q system=n water ( Δ fush)= 8g 18g h) What is q surroundings in Joules? q surroundings = q system=9.kj 15. ( at home)calculate the heat (q) in joules that is involved in cooling 8g of liquid water starting at 10. C to ice at 0. C.?(Answer:11kJ) Practice problems: 16. Calculate the energy needed, in kj, to heat 6 g of water from 50 o C to 100 o C and then to completely vaporize it to steam at 100 o C. The specific heat of water is.18 J/(K g) and its enthalpy change of vaporization is 0.7 kj/. (Answer:89kJ) J 0.7kJ 1000J q= 6gH 50K.18 6gH 88. 9kJ K g 18gH 1kJ 17. If. kj of energy is add to 1.0 kg of water (C =.18 J/(gK)), initially at 5 o C. a) What is the final temperature of the water (in K)??(Answer:08) T=75 needed to get to boiling it will require q heating=1000 g J/(gK)=1800J=1.8kJ q heating=1000g kg T.18 J/(gK)=000J; T=10.0K T=T finalt initial= T final5 T final=5+7.15=08k 5

6 b) The same amount of energy was added to.0 kg of an unknown substance and its temperature increased by 6 C. What is the specific heat of the unknown substance (in J/(gK))?(Answer:.5) q heating=000g kg 6K c( J/(g K))=000J; c=.5 J/(g K) 18. You are given L of a 0.05 M HCl solution. You are also given a 0.5M solution of barium hydroxide. What volume (in L) of the Ba(H) (aq) solution is required to completely react with the HCl solution, with no HCl or Ba(H) remaining in solution?(answer:100ml) 0.05HCl 1Ba ( H) Ba( H) LHCl 0. HCl Cl H 0.5Ba ( H) 19. If of 0.5 M solution of the unknown acid HA produces 0.05M concentration of the hydronium ion what is the percent of the acid reacted? Is the unknown acid a strong or weak electrolyte? 0.05MH 100% 10.% 0.5Macid 0. How many grams of Ba(H) is needed to be mixed with 0 ml of water to produce 0.05M solution of hydroxide. (Answer: 0.85g) 0.05H 1Ba ( H) 171gBa ( H) 0.0LH g H H 1Ba ( H) 1. Calculate the sodium ion concentration when 70. ml of.0 M sodium carbonate is added to 0. ml of 1.0 M sodium nitrate.(answer:.5m).0na C Na 1.0NaN 1Na 70mlNaC 0mlNaN 1Na C 1NaN =0.50 Na + (aq) [Na + (aq) ]= 0.5/0.=.5M a) To the sodium carbonate and sodium nitrate solution, you add 0.0 es of solid BaCl. What is the final concentration of each of the ions in the solution? Assume the solid BaCl does not change the volume. (Answer:0.0, 0, 0.10 ) Ba + (aq) + C (aq) Ba C(s)ppt Start: 0.0(L.R.) 0.1(excess).0Na C 1C ( 70mLNaC ) 1Na C [Na + (aq) ]= 0.5/0.=.5M [Ba + ]=0M [C ]=0.01/0.=0.1M [N 1.0NaN 1N ]=(0mlNaN ) / M 1NaN 6

7 H=7.8 =0. A 0. sample of an acid HA is added to 500. ml of water and only 0.01% of the acid reacts. How many es of HA, A, H +, and H are present at the end of the reaction? % 5 10 reacted 100% HA = 0. =0. 5 A = 10 H + = + = In preparation for next week material not part of exam.. During the chemical reaction thermometer in a beaker showed the increase in temperature by 10. C. Choose all that apply: q sys < 0 q sur > 0 T sys = 0 T sur > 0 We know nothing about work.. Reaction takes place in the balloon. During the reaction balloon expands. Choose all that apply: q sys, q sur are not defined w < 0 T sys = 0 T sur not defined 5. A combustion reaction takes place in the balloon. During the reaction balloon expands. Choose all that apply: q sys < 0 q sur > 0 w < 0 T sys = 0 T sur > 0 7