HW1 Ans

# HW1 Ans - Water l Solubility of Ethanol in Water Explain...

This preview shows pages 1–3. Sign up to view the full content.

Water l. Solubility of Ethanol in Water Explain why ethanol (CHBCH2OFI) is more soluble in water than is ethane (CH3CH3). Answer Ethanol is polar; ethane is not. The ethanol -OH group can hydrogen-bond with water. 2. Calculation of pH from Hydrogen Ion Coneentration What is the pH of a solution that has an H+ concentration of (a) I.75 x 10-5 mol/L; (b) 6.50 x 10-10 moVL; (c) 1.0 x l0-4 mol/L; (d) 1.50 x 10-5 mol/L? Answer Using pH = -log [H*]: (a) -log (1.?5 x 10-5) : 4.76; (b) -log (6.50 x 10-10) 9.19;(c) -log (1.0 x 10-a; 4.6' (d) -log (1.50 x 10-5) 4.82. 3. Calculation of Hydrogen Ion Concentration from pH What is the H* concentration of a solution with pH of (a) 3.82; (b) 6.52; (c) 11.11? Answer Using [H+] - IO-PH: [H*] :10-3'82:1.51 x 10-4M;(b) 1g-6'sz =3.02 x l0-7u; (c) 10-rr'rr :7.76 x 1o-12 rrl. H 4. Acidity of Gastric HCI In a hospital laboratory a 10.0 mL sample of gastric juice, obtained several rr hours after a meal, was titrated with 0.1 rrr NaOH to neutrality;7.2 mL of NaOH was required. The pa- tient's stomach contained no ingested food or drink, thus assume that no buffers were present. What was the pH of the gastric juice? Answer Multiplying volume (L) by molar concentration (mol/L) gives the number of moles in that volume of solution. If r is the concentration of gastric HCI (mol,/L), (0.010 L)x: (0.0072 L)(0.1 moVL) n 0.072 tr.l gastric HCI Given that pH and that HCI is a strong acid, pH: -log (7.2x 10-2;:1.1 5. Calculation of the pH of a Strong Acid or Base (a) Write out the acid dissociation reaction for hydrochloric acid. (b) Calculate the pH of a solution of 5,0 x 10-a lt HCl. (c) Write out the acid dissociation for sodium hydroxide. (d) Calculate the pH of a solution of 7.0 x 10-5 lr NaOH. s-13

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
S-14 Chapter 2 ttlater Answer (a) HCI -.- H+ + Cl- (b) HCI is a strong acid and firlly dissociates into H+ and Cl-. Thus, [H*] : [Cl-] = tHCll. pH : -log -log (5.0 x 10-4 u) 3.3 (two significant figures) (c) NaOH -.- Na+ + OH- (d) is a strong base; dissociation in aqueous solution is essentially complete, so lNa+1 :[OH-1 :[NaOH]. PH+POH:14 pOH: -log [OH-] pH t4 + log 14 + log (7.0 x 10-5) 9.8 (two signilicant Calculation of pH from Concentration of Strong Acid Calculate the pH of a solution prepared by diluting 3.0 mL of 2.5 w HCI to a final volume of 100 mL with HzO. Answer Because HCI is a strong acid, it dissociates completely to H* + Cl-. Therefore, 3.0 mL x 2.5 M HCI 7.5 meq of H*. In 100 mL of solution, this is 0.075 ru H+. pH: -log : -log (0.075) : -(-1.1) : 1.1 (twosignilicantfigures) Measurement of Acetyleholine Levels by pH Changes The concentration of acetylcholine (a neurotransmitter) in a sample can be determined from the pH changes that accompany its hydrolysis. When the sample is incubated with the enz],rne acetylcholinesterase, acetylcholine is quantitatively converted into choline and acetic acid, which dissociates to yield acetate and a hydrogen ion: 6. t. o 9H' cH.-C-o-cH2-cH2-*rf-cH. I'o- -l Acetylcholine CH' ?"' HO-CH2-CH2-*T-CH3 + CH, Choline : CH3-C-O- + 11* tl o Acetate 'J In a typical analysis, 15 mL of an aqueous solution containing an unknown amount Qf bcetylcholine had a pH of 7.65. When incubated with acetylcholinesterase, the pH of the solution decr64sed to 6.87. As- suming that there was-no buffer in the assay mixture, determine the number of moles of acetylcholihe in the 15 mL sample.
This is the end of the preview. Sign up to access the rest of the document.

## This note was uploaded on 10/22/2009 for the course CHEM 140A taught by Professor Whiteshell during the Spring '04 term at UCSD.

### Page1 / 13

HW1 Ans - Water l Solubility of Ethanol in Water Explain...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online