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![CH111-2nd Summerterm 2017 Take-Home Acid-Base Problem-Solving Assignment You must show& submit all work for the following problems at the beginning of your lab period on Wednesday 8/217, They will NOT be accepted late. The instructor will not give full credit for any problem that is identical to another persons work or that does not show the logical analysis, even if the numerical result is correct. These problems are worth 2 points. Be sure to show all your work and use proper units, labels and significant figures Remember tables of acid/base dissociation constants are located in Appendix D.1& D2 p 1103-4 in your textbook. 1. Consider the following salts: KCN (CH,NH) Br MgClh a. For each salt, identify the ions produced when each salt is placed in water and the salt completely nizes (Do NOT write the reaction with water). For example Naci ionizes to form [N, and C r] b. Identify each salt solution produced as aciíc, neutral or basic. (hint: p。702-704) 2 Calculate the pH of a buffer that is 0.355 M CH COOH and 0.288 M NaCH COO. 3. Calculate the pH of a buffer that is 0.321 NHs AND 0.123M NH4CL 4. What is the pH of a buffer produced by mixing 150 mL of 0.421 NHs and 175 mL of 0.157 NH,CI? Be sure to first find the concentration of each compound in the mixed solution (MM-MM where va equals the total volume), then apply equilibrium 5 What is the pH of a buffer produced by mixing 275 ml of 0277 M HCOOH AND 300 mL of 0.203 M KCOOH ? Be sure to first find the concentration of each compound in the mixed solution (MM Mav, remember v, total volume), then apply equilibrium.](https://media.cheggcdn.com/media%2F21f%2F21f7282c-aab1-449c-b215-c1841cfdeca3%2Fimage)
Consider the following salts: NH_4Cl NaCHO_2 [or NaHCOO] KCN LiNO_3 (CH_3NH_3) Br MgCl_2 a. For each salt, identify the ions produced when each salt is placed in water and the salt completely ionizes (Do NOT write the reaction with water). For example NaCl ionizes to form [Na^+1, and Cr^-1] b. Identify each salt solution produced as acidic, neutral or basic. Calculate the pH of a buffer that is 0.355 M CH_3COOH and 0.288 M NaCH_3COO. Calculate the pH of a buffer that is 0.321 NH_3 AND 0.123M NH_4CL What is the pH of a buffer produced by mixing 150 mL of 0.421 NH_3 and 175 mL of 0.157 NH_4CI? Be sure to first find the concentration of each compound in the mixed solution (M_1V_1 = M_2V_2 where V_2 equals the total volume), then apply equilibrium. What is the pH of a buffer produced by mixing 275 ml of 0.277 M HCOOH AND 300 mL of 0.203 M KCOOH ? Be sure to first find the concentration of each compound in the mixed solution (M_1V_1 = M_2V_2 remember V_2, total volume), then apply equilibrium.
Expert Answer
Solution:
Ans to Question No 1(a)
NH4Cl: ionizes to form NH4+1 and Cl-1
NaHCOO ionizes to form Na+1 and HCOO-1
KCN ionizes to form K+1 and CN-1
LiNO3 ionizes to form Li+1 and NO3-1
(CH3NH3)Br ionizes to form CH3NH3+1 and Br-1
MgCl2 ionizes to form mg+2 and 2Cl-1
Ans to Question No 1(b)
| salt | Parent acid | Parent base | pH
salt |
| NH4Cl | HCl strong acid | NH4OH weak base | Acidic |
| NaHCOO | HCOOH weak | NaOH strong base | basic |
| KCN | HCN weak | KOH strong base | basic |
| LiNO3 | HNO3 strong | LiOH strong base | neutral |
| (CH3NH3)Br | HBr strong acid | CH3NH2 weak base | Acidic |
| MgCl2 | HCl strong | Mg(OH)2 weak base | acidic |
Ans to Question No 2.
Using Henderson–Hasselbalch equation we get
pH = pKa + log ([A-] / [HA])
pH = 4.74 + log (0.288 / 0.355 ) (The pKa of CH3COOH is 4.74.)
pH = 4.74 – 0.091
= 4.649
Ans to Question No 3:
Using Henderson–Hasselbalch equation we get
pH = pKa + log ([A-] / [HA])
pH = pKa + log [NH3 ] [NH4 +] (The pKa of CH3COOH is 9.24.)
= 9.24 + log (0.321/0.123)
= 9.24 + 0.416
= 9.656
