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Saint Clair College of Applied Arts and Technology CHM 327 Analytical Chemistry I Test 4 NAME:___________________________ FOR EACH QUESTION, YOU MUST SHOW YOUR WORK TO GET FULL MARKS 1. How many Na+ ions are contained in 5.34 mole of Na3PO4 (MW=163.945 g/mol) given that 1 mole contains 6.02 x 1023 ions/molecules)? (4) 2. What is the mass in milligrams of solute in 6.75 mL of 0.0619 M KNO3 (MW=101.10 g/mol)? (4) 3. What KHP mass (MW=204.22 g/mole) is required to neutralize 15.00 mL of 0.01247 M HCl? (4) 4. Twenty-five milliliters of a 0.1123 M solution of HCl are diluted in a 100.0 mL volumetric flask. A solution containing sodium hydroxide (MW=40.00 g/mol) requires 25.76 mL of the dilute HCl for neutralization. How many milligrams of NaOH are in the sodium hydroxide solution? (5) 5. You are required to manufacture a 5.0 ppm (w/v) solution of NaOH. How much NaOH (mg) must be placed in a 100.0 mL volumetric flask to make this solution? (3) 1 6. What volume of 0.01227 M HCl would be required to titrate 25.00 mL of the solution manufactured in Question 5? (5) 7. Show the overall chemical equation that describes the reaction between sodium carbonate and hydrochloric acid in aqueous solution. (4) 8. What Na2CO3 mass (MW=105.9 g/mole) is required to neutralize 22.31 mL of 0.1017 M HCl? What type of indicator would you use for this titration? Why? (7) 9. 5.3573 grams of Na2CO3 (MW=105.9 g/mole) are placed in a 1.0 L volumetric flask. A 25.00 mL aliquot of this solution is neutralized with 11.55 mL of HCl. What is the molarity of the HCl solution? (5) 2 10. A 0.3731 g mass of EDTA (MW = 372.240 g/mol) is made up to volume in a 100.0 mL volumetric flask. a. Calculate MEDTA through molecular weight. (2) b. A solution of 0.2588 g CaCO3 (MW = 100.087 g/mol) has its CO2 evolved using HCl and is then neutralized and made to 100.0 mL. Five 10.00 mL aliquots are titrated with EBT indicator generating the following results: (10) VCaCO3 (mL) VEDTA (mL) 10.00 24.87 10.00 24.58 10.00 25.25 10.0 24.65 10.0 25.01 MEDTA avg MEDTA s 90% 95% 99% Complete the above table by calculating MEDTA for each titration. Calculate the average MEDTA and (after calculating s) the 90, 95 and 99 % confidence limits of the mean (given the t values for 5 observations as: 90% t = 2.13; 95% t = 2.78; and for 99% t = 4.60. 3 11. Generally speaking, what do all Ion Selective Electrodes measure? (1) 12. What is a reference electrode and what is the potential that it generates compared to? (2) 13. Why is the order in which solutions are measured by electrodes important? (1) 14. Why is electrode “slope” important? How is the electrode slope value obtained? (3) 15. Why is KCl usually added a to the reference electrode’s inner chamber? (1) 16. A drinking water sample is thought to contain over the desired limit of 0.25 mg/L (0.25 g/mL or 0.25 ppm w/v) fluoride (F-). An ISE measurement is to be completed on the sample using NaF to manufacture the calibration standards. a. What mass of NaF reagent (MW F = 19.00 g/mol; MW Na = 23.00 g/mol) must be used to create a 1,000 ppm stock standard of fluoride (F-) in a 100.0 mL volumetric flask? (6) b. What aliquot must be taken from the stock solution to make an intermediate stock standard of 100.0 ppm as fluoride (F-) in a 100.0 mL volumetric flask? (4) c. From the intermediate stock standard (100 g/mL) what aliquot volumes are required to produce standards of 1.00, 5.00 and 10.0 ppm fluoride (F-) in 100.0 mL volumetric flasks? (8) 4 17. The calibration line’s regression equation was generated from the potentiometric analysis of the solutions described in Q16. It was found to be linear in the following form: Y = 162.2 – 55.85logX. a. A potentiometric value of 168.5 mV was measured in the drinking water sample from Q16. Using the linear regression equation, calculate the fluoride concentration (g/mL or ppm) in the sample from this mV potential. (6) b. Is the fluoride concentration found in Q17 a) above the desired fluoride concentration of 0.25 ppm? If so, describe by how much as a percentage. (6) c. A potentiometric value of 184.9 mV was measured in a tap water sample taken from a faucet in the lab. Using the linear regression equation, calculate the fluoride concentration (g/mL or ppm) in the sample. (6) d. Is this concentration in 17 c) above the desired fluoride concentration? What should this value be reported as? (3) 5 18. Use a figure (diagram) to illustrate the apparatus that would have been used to gather the mV potentials in the solutions in Q17. Include a brief description of the function of each of the items in your figure. (6) 19. A solution of sodium thiosulfate was standardized using 0.2210 g of potassium iodate (MW = 214.00 g/mol) in water with excess KI and HCl for acidification. The liberated I2 was titrated with 41.64 mL of sodium thiosulfate. a. Show the reaction equations involving iodine liberation and subsequent thiosulfate titration. (4) b. Calculate Mthio. (5) 6 20. A mass of 2.210 g KBrO3 (MW = 167.001 g/mol) is placed in a 250.0 mL volumetric flask. A 10.00 mL aliquot is removed and placed in 100 mL of water containing excess KI and acid. The liberated iodine requires 23.32 mL of thiosulfate for complete reaction. a. Calculate Mthio. (6) b. What indicator is used for this titration? Describe the indicator colour before titration point is reached and why (how) this colour is generated. (3) c. Why is important to add the indicator just before reaction is complete? (1) 21. A mass of 1.225 g of sodium oxalate (MW = 134.00 mg/mol) is placed in a 100.0 mL volumetric flask. A 10.00 mL aliquot is placed in 100 mL of water and titrated with 32.99 mL of potassium permanganate. a. Show the reaction equation between potassium permanganate and sodium oxalate. (4) b. What is MKMnO4? (8) 7 22. Write balanced net ionic equations for the following reactions. Identify the oxidation and reduction for each reaction. a. Cl- + MnO2(s) Cl2(g) + Mn2+ (6) b. IO3- + I- I2(aq) (6) c. IO3- + I- + Cl- ICl2(6) d. I2 + H2S I- + S(s) (6) BONUS: Who was St. Nickolas? (1) 8