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Question 1 10 /^10 pts
CHEM 104 chemistry ii Exam 2 Portage Learning
Questions and Verified Answers, 100% Pass
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Due No due date Points 100 Questions 10 Time Limit 120 Minutes
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Click this link to access the Periodic Table. (https://previous.nursingabc.com/upload/images/Help_file_picture/Periodic_Table.pdf) This may be helpful throughout the exam. Identify each of the compounds below as ACID, BASE or SALT on the basis of their formula and explain your answer. (1) HMnO 4 (2) CaCr 2 O 7 (3) LiOH Your Answer:
- acid - ionizable H+ means acid, permanganic acid
- salt - because neutral and produced from calcium hydroxide (base) and hydrogen dichromate (acid)
- base - because the OH, contains metal Li
Question 2 10 /^10 pts
Click this link to access the Periodic Table. (https://previous.nursingabc.com/upload/images/Help_file_picture/Periodic_Table.pdf) This may be helpful throughout the exam. For the Brønsted-Lowry acid base reactions shown below, list the stronger acid, stronger base, weaker acid and weaker base in the answer blanks provided: HS-^ + HCN CN-^ + H 2 S Stronger acid: Stronger base: Weaker acid: Weaker base: Your Answer: HS - weaker base HCN
- weaker acid CN - stronger base H2S - stronger acid HMnO 4 (MnO 4 ) group (Cr 2 O 7 ) LiOH group Acid Contains H + Polyatomic group Salt Contains Metal (Ca) + Polyatomic Base Contains Metal (Li) + OH Polyatomic
Stronger acid is:
Question 4 8 /^10 pts
Click this link to access the Periodic Table. (https://previous.nursingabc.com/upload/images/Help_file_picture/Periodic_Table.pdf) This may be helpful throughout the exam. Show the calculation of the [H+] and pH of a 0.00350 M solution of the strong acid H 2 SO 4. Your Answer: Explanation: Formula of conjugate base of the stronger acid: Your Answer: Stronger acid is: AsH Explanation: the size of As is bigger among N, P and As and as size increases bonding with H+ becomes less strong as small atoms forms stronger bonds with H+ as hybridization is stronger between atoms of the same size. so AS-H bond dissociation enthalpy decreaes hense acidity increases. AsH3 ---> AsH2- (conjugate base) Stronger acid is: AsH 3 Explanation: As is the largest atom (of N, P or As) which makes the H-As bond weakest and most likely to form H+ Formula of conjugate base of stronger acid: conjugate base of AsH 3 is AsH 2 -
Question 5 10 /^10 pts
Click this link to access the Periodic Table. (https://previous.nursingabc.com/upload/images/Help_file_picture/Periodic_Table.pdf) This may be helpful throughout the exam. In the titration of 0.300 grams of Al(OH) 3 in the presence of bromothymol blue indicator, the blue solution turns yellow after 26.4 mL of HCl of unknown concentration is added. Show the calculation of the molarity of the HCl solution. Your Answer: moles of Al(OH)3 = 0.3 / 78 = 3.85 x 10^-3moles of Al(OH)3 Al(OH)3 + 3 HCl --> AlCl3 + 3 H2O 1 mol Al(OH)3 ---> 3 mol HCl [H+] = 2 x [H 2 SO 4 ] = 0.00700 M 2. pH = - log (0.00700) =
0.00350 M
Now, pH = - log [H+] = - log (0.00350) = 2. concentratio of H+ = [H+] = 0.00350 M and pH of the solution is 2.45 or
Failed to multiple the concentrations of protons by 2; minus 3 points.
Question 6 9 /^10 pts
Click this link to access the Periodic Table. (https://previous.nursingabc.com/upload/images/Help_file_picture/Periodic_Table.pdf) This may be helpful throughout the exam. Show the calculation of the [OH-], pH and % ionization for 0.457 M ammonia (NH 3 ) NH 3 + H 2 O (^) (liq) NH +^ + OH-^ K = 1.8 x 10 - 4 a 5 Your Answer: Ka = (OH-) ^2/ 0.475 = 1.8 x 10^(-5) [OH- ] = 0.0029M POH = - log [OH-] = 2.54 pH= 14 - POH = 11. 3.85 x 10^- 3 Al(OH)3 ---- > ?moles HCl moles of HCL = 3.85 x 10^ - 3 x 3 = 0. volume of HCl = 26.4 mL = 0.0264 L Molarity = moles/ volume = 0.01154/ 0. = 0.437 M of HCl solution ( H Cl is the acid and Al (OH) 3 is the base) Ma x mLa / 1000 x Sa / Sb = gb / MWb Ma x 26.4 / 1000 x 1 / 3 = 0.300 / 78. MHCl = 0.437 M
Question 8 10 /^10 pts
Click this link to access the Periodic Table. (https://previous.nursingabc.com/upload/images/Help_file_picture/Periodic_Table.pdf) This may be helpful throughout the exam. Show calculation of the pH of a buffer prepared by mixing 0.080 M NaC 2 H 3 O 2 and 0.060 M HC 2 H 3 O 2. HC 2 H 3 O 2 H+^ + C 2 H 3 O - 2 Ka = 1.8 x 10 -^5 Your Answer: using the Henderson Hasselbalch equation: pH = PKa + log (base-/acid) Predict and explain whether a solution of NH 4 Cl is acidic, basic or neutral. Your Answer: NH4Cl is a salt of a weak base NH4OH and a strong acid HCl. When NH4Cl is dissolved in H2O the following reaction will be present in the solution: NH4Cl + 2H2O --> NH4OH + HCl Since HCl is a strong acid it is mainly present as H+ and Cl- ions. And NH4OH does not ionize fully because H+ ions are in excess over OH- ions. This will make the solution acidic. NH 4 Cl: Acidic since NH 4 hydrolyzes to form a weak base (NH 4 OH) and H 3 O+
- = - log (1.8 x 10^ (-5) + log (0.08/ 0.06) 4.
H2O (liq) < --------------- > NH4+ + OH-
pOH = - log [OH-] = - log (2.70 x 10 -^5 ) = 4. pH = 14 - pOH = 14 - 4.57 = 9.
= [OH-]
(0.210) x = 2.70 x 10 -^5 1.8 x 10 -^5 = (0.140) (x) x = (1.8 x 10 -^5 ) (0.210) / (0.140) (0.140 + x) (x) (0.210 - x)
[NH 3 ] NH 3 + H 2 O^ (liq) NH 4 + + OH^ - The OH- reacts with H+ and decreases [OH-] and shifts equilibrium to the products/ right. [NH4+] will increase by 0.0100M and NH3 will decrease by the same. The new concentratiosn are as follows: [NH4+] = 0.150 + 0.0100 = 0.160M [NH3] = 0.200 - 0.0100= 0.190M then [H+] = [NH3]/[NH4+] x Ka --> 0.190/0.160 x 1.8x10^(-5) = 2.1375 x 10^ (-5) Ph = - log [H+] =- log [ 2.1375 x 10 ^(-5) ph =
Incorrect application of buffer equation; solved for [H+] and not [OH-]. Minus 4 points.
Your Answer:
Quiz Score: 93 out of 100 The location of the equivalence point is at approximately pH 8.5, indicates that this is a weak acid with a strong base. The indicator should be phenolphthalein. The rapid rise occurse approsimately between pH 7 and pH 10. The indicator chosen should change color within pH7 - pH10 which corresponds to phenolphthalein. The other indicators are not in this range and not selected. The equivalence point at pH > 7, shows that this is a weak acid / strong base titration. The rapid rise occurs approximately between pH 7 and pH 11. The indicator should change color within that range so we should choose Phenolphthalein.
