2. The standard Winkler method uses sodium iodide and sodium azide to be added at the same time as sodium hydroxide. What is the purpose of sodium azide? 3. Chlorinated tap water contains both chlorine (Cl2) and hypochlorite (OCl-) does the presence of these species affect DO results? Write equations to represent their individual interactions.

2. The standard Winkler method uses sodium iodide and sodium azide to be added at the same time as sodium hydroxide. What is the purpose of sodium azide? 3. Chlorinated tap water contains both chlorine (Cl2) and hypochlorite (OCl-) does the presence of these species affect DO results? Write equations to represent their individual interactions.

Chemistry & Chemical Reactivity

10th Edition

ISBN:9781337399074

Author:John C. Kotz, Paul M. Treichel, John Townsend, David Treichel

Publisher:John C. Kotz, Paul M. Treichel, John Townsend, David Treichel

Chapter4: Stoichiometry: Quantitative Information About Chemical Reactions

Section4.9: Spectrophotometry

Problem 3.1ACP

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1. What are some precautions that should be observed when collecting samples for DO determination, to ensure the amount of oxygen in the sample is representative of the DO at the site? 2. The standard Winkler method uses sodium iodide and sodium azide to be added at the same time as sodium hydroxide. What is the purpose of sodium azide? 3. Chlorinated tap water contains both chlorine (Cl2) and hypochlorite (OCl-) does the presence of these species affect DO results? Write equations to represent their individual interactions. 4. What effect would nitrate (NO2-), a common constituent of polluted water, have on DO results? Write a balanced equation for its interaction. 5. What is meant by seawater intrusion in drinking water supplies? How does this happen? What are some consequences of these phenomena?
Accurately weigh out about 6g copper(ii) sulfate crystals into a weighing boat. Use the copper(ii) sulfate crystals to make up 250cm3 of standardized copper (ii) sulfate solution Pipette 25cm3 of this solution into a conical flask Add 1.5g potassium iodide and swirl thoroughly Titrate this solution with standard 0.1 moldm-3 Na2S2O3 in a burette. When the iodine color fades, add 1 cm3 starch indicator. Use your titration data below to calculate the percentage by mass of copper in the copper(ii) sulfate crystals.
A piece of Gold weighing 12,359 Kg is suspected of being contaminated with Iron. To perform an instrumental analysis and To confirm whether or not it contains Fe, a portion of the sample (0.954 g) is taken from the piece and dissolved with 25 mL of aqua regia. Heats up For its complete dissolution, it is cooled and made up to 100 mL. A 10 mL aliquot is taken from this solution and made up to 50 mL. From This last solution is given the appropriate treatment to visualize Fe+2, for which the 1,10-phenanthroline reagent is added. (it forms a complex that is red in color) and is taken to a visible spectrophotometer and with a 12 mm cell a absorbance of 0.45. Previously, a calibration curve of Fe+2 was obtained under the same instrumental conditions obtaining the following data: (view table) Calculate the purity of the gold piece, assuming impurities only due to Fe.
Volumetric Analysis The mass of KHC8H4O4 is measured to the nearest milligram; however, the volume of water in which it is dissolved is never of concern—water is even added to the wall of the Erlenmeyer flask during the titration. Explain why water added to the KHC8H4O4 has no effect on the data, whereas water added to the NaOH solution, may drastically affect the data.
The test tube used in the determination of the ΔHrxn for nitric acid was still wet with water. [ magnitude of ΔHrxn] Please explain why the reaction decreases. Maximum of 3 sentences only.
The NaOH titrant in this experiment was prepared to be approximately 0.1 M and then was standardized to determine its exact concentration. What possible reasons could there be for not simply weighing the solid NaOH, dissolving to a known volume and calculating its molarity?
An auxiliary competing agent is used in EDTA titrations to slow down the titration. keep some interfering component of the analyte mixture from complexing with the EDTA. speed up the titration. keep the metal ion from precipitating out of the solution.
In this experiment, you will take a 25.00 mL aliquot of vinegar and dilute it to 250.0 mL. You will then take a 25.00 mL aliquot from this diluted vinegar solution and titrate it against the standardised sodium hydroxide. The titration between acetic acid and sodium hydroxide is a 1:1 stoichiometry. If your standardised sodium hydroxide solution was determined to be 0.060 M, and it required an average titre (titration volume) of 20.3 mL, what is the concentration (in M) of the undiluted vinegar sample (the initial vinegar sample)? Provide your answer to 2 significant figures.
What is the purpose of adding NaOH to the filtrate? To increase the pH of the fermenting solution (increase its basicity) To decrease the pH of the fermenting solution (increase its acidity) To maintain the optimal pH of the fermenting solution, which is 4.5 To remove impurities and by-products in the filtrate.
25.00 mL of a saturated Ca(OH)2 sample requires 22.50 mL of 0.0250 M HCl to neutralize it. Calculate the value for Ksp of Ca(OH)2 from this data. Given the equilibrium equation: Ca(OH)2 (s) ↔ Ca2+ (aq) + 2OH– (aq) Use moles of OH¯ and sample volume to determine [OH¯]:
TRUE OR FALSE 1. Sodium arsenite is formed due to the solubility property of arsenic trioxide in sodium hydroxide. 2. The permanganate method is always carried out in a highly acidic medium. 3. The color of permanganate solution renders impossible accurate readings at the lower meniscus. 4. Sodium bicarbonate in the standardization of iodine solution acts as a buffer. 5. Sulfuric acid in permanganate titration prevents the formation of reduction products.
0.75 gm of calcium carbonate is dissolved in 1 liter of distilled water. 100 ml of this standard hard water requires 25 ml of EDTA solution. 100 ml of unknown hard water requires 15 ml of EDTA solution. 100 ml of same water sample after boiling requires 10 ml of EDTA solution. Calculate Total, Permanent and Temporary hardness of water sample.