Homework 2

ENV3001 Homework 2 1. (12 points) Identify each of the following situations as being “ethical” or “not ethical” (write a capital “E” or “N” in front of the letter of each statement, respectively). ( ) a) Students studying together to help each other learn ( ) b) One student copying homework from another ( ) c) One student peeking into another’s test paper during an exam ( ) d) Obtaining a term paper from the internet and turning it in as your own work ( ) e) Signing and sealing engineering plans done by someone else who worked under your supervision. ( ) f) Signing and sealing engineering plans done by someone else who did not work under your supervision. 2. (10 points) What is the pH of the following solution: 0.07 M HClO3 (weak acid pKA = 7.6) Page 1 of 5 ENV3001 Homework 2 3. (12 points) The weak acid hypochlorous acid (HOCl) has a pKA of 7.54 (HOCl ↔ H++OCl-). If you mix 20 g of HOCl into enough water to make 1 L of solutions, what will be the final pH? The atomic weights are H=1, O=16, Cl=35.5). 4. (10 points) The compound C7H4N3O6 burns explosively with oxygen to produce CO2, H2O, and N2. Write a balanced chemical equation for this reaction and calculate the mass of oxygen required (in grams) to burn 113 g of this compound. Page 2 of 5 ENV3001 Homework 2 5. (12 points) One method of removing phosphate from wastewater effluent is to precipitate it with aluminium sulfate (alum). A possible stoichiometry (but not exact because aluminium and phosphate can form many different chemical materials) is: 2 PO43- + Al2(SO4)3 → 2 AlPO4 + 3 SO42If the concentration of phosphate (PO43-) is 50 mg/L, how many kg of alum must be purchased annually to treat 40L/s of wastewater? How many kg/yr of solid precipitate will be formed (dry basis) if all of the phosphate is precipitated as AlPO4? 6. Calculate the pH of: a) (10 point) 0.002 molar concentration of KOH (a strong base) KOH ↔ K+ + OH¯ Page 3 of 5 ENV3001 Homework 2 b) (10 points) 0.004 molar concentration of HC2H3O2 (a weak acid, Ka = 2.5 × 10-5) HC2H3O2 ↔ H+ + C2H3O2- 7. (10 point) Calculate the equilibrium concentration (in mol/L) of metal nickel (Ni) ion in a solution made from mixing solid Ni(OH)2 in water. Ksp of = 5.5×10-16 Ni(OH)2 ↔ Ni+2 + 2OH¯ Page 4 of 5 ENV3001 Homework 2 8. (14 points) In treating an industrial wastewater, we add NaOH to remove Cr3+ ions (atomic weight) = 52). The chemical equation for the dissolution of Cr(OH)3 is Cr(OH)3 (s) ↔ Cr3+ + 3OH- (Ksp = 6.7×10-31) What is the final equilibrium concentration (in mg/L) of Cr3+ ions in a solution of Cr(OH)3 when the water has a pH of 4? Page 5 of 5