1. (10) The amount of protein in a sample of cheese can be determined by Kjeldahl analysis for nitrogen. After digesting a 0.9814-g sample of cheese, the nitrogen is oxidized to NH4*, converted to NH3 with NAOH, and distilled into a collection flask containing 50.00 mL of 0.1047 M HCl. The excess HCl is then back-titrated with 0.1183 M NaOH, requiring 22.84 mL to reach the bromthymol blue end point. Report the % (w/w) protein in the cheese given that there is typically 6.38 g of protein for every gram of nitrogen in most dairy products.

1. (10) The amount of protein in a sample of cheese can be determined by Kjeldahl analysis for nitrogen. After digesting a 0.9814-g sample of cheese, the nitrogen is oxidized to NH4*, converted to NH3 with NAOH, and distilled into a collection flask containing 50.00 mL of 0.1047 M HCl. The excess HCl is then back-titrated with 0.1183 M NaOH, requiring 22.84 mL to reach the bromthymol blue end point. Report the % (w/w) protein in the cheese given that there is typically 6.38 g of protein for every gram of nitrogen in most dairy products.

Fundamentals Of Analytical Chemistry

9th Edition

ISBN:9781285640686

Author:Skoog

Publisher:Skoog

Chapter16: Applications Of Neutralization Titrations

Section: Chapter Questions

Problem 16.20QAP

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A volume of 50 mL of 1.8 M NH3 is mixed with an equal volume of a solution containing 0.95 g of MgCl2. What mass of NH4Cl must be added to the resulting solution to prevent the precipitation of Mg(OH)2?
A 0.5843-g sample of a plant food preparation was analyzed for its N content by the Kjeldahl method, the liberated NH3 being collected in 50.00 mL of 0.1062 M HCl. The excess acid required an 11.89 mL back-titration with 0.0925 M NaOH. Express the results of this analysis in terms of (a) %N (b) %urea, H2NCONH2 (c) %(NH4)2SO4 (d) %(NH4)3PO4
3) In the treatment of myasthenia gravis, 10 mg of guanidine (NH-C(NH2)2) per kilogram of body weight is given. Nitrogen in a sample with a total mass of 7.50 g and containing 4 tablets is converted to ammonia by Kjeldahl decomposition. It is then distilled into 100 mL of 0.1750 M HCI. Performed analysis; titration of excess acid with 11.37 mL of 0.180 M NaOH solution. Accordingly, in which option is the number of tablets at the appropriate dose given for a 48 kg patient? (C-12.0 g/mol; H=1 g/mol; N = 14.0 g/mol; Cl=35,5 g/mol) a) 3 b) 6 c) 9 d) 12 f) 15
(6) 0.8203 g NaAc (FW=82.03 g/mol) was fully dissolved into 100.00 mL of 0.050 M HAc solution. Calculate th pH of the soolution.
What minimum volume of 0.09621 M AgNO3 willbe needed to assure an excess of silver ion in the titration of: (a) an impure NaCl sample that weighs 0.2513 g?(b) a 0.3462-g sample that is 74.52% (w/w) ZnCl2?(c) 25.00 mL of 0.01907 M AlCl3?
(a) In performing a titration, why is it better to use a solution of a concentration such that 30-45 mL is required, instead of a more concentrated solution that might only require about 5 mL to reach the end point? (b) To make a standardized NaOH solution, why is it better to prepare a NaOH solution of approxi- mate concentration and then standardize with KHP, rather than to weigh accurately some NAOH pellets, dissolve them, and dilute the solution in a volumetric flask? (c ) In analyzing a 0.003 weak acid by titration with 0.00300 M NaOH, why would you be able to obtain greater accuracy by using a pH meter instead of using a color-change indicator such as phenolphthalein?
A dilute solution of NaOH is titrated with 0.9050 g primary standard potassium hydrogen phthalate (KHP, C8H5K04, FW=204.23 g/mol) which required 10.50 mL of the base using phenolphthalein indicator. (a) What is the color at the endpoint? (b) What is the molar concentration of the titrant?
A mixture of 500.0 mg acid A and 250.0 mg acid B is titrated with 0.1150 N NaOH. The endpoint is overstepped on the addition of 45.30 mL of the base. The solution is backtitrated using 1.40 mL of 0.1234 N HCl solution. If the equivalent weight of A is thrice the equivalent mass of B, calculate the equivalent weights of A and B.
A sample of meat scrap weighing 2.000 g is digested with concentrated sulfuric acid and a catalyst. The resulting solution is made alkaline with NaOH and the liberated ammonia distilled into 50.00 mL of 0.6700 N HCl. The excess acid then requires 30.10 mL of 0.6520 N NaOH for neutralization. What is the percentage of the protein in the meat? The Kjeldahl factor is 6.25. (pls answer thanku)
Zhongli is a speleologist tasked to analyze the CaCO₃ content of a limestone stalactite. A 5.0000-g sample was dissolved in 25.00 mL of 1.350 M HCl, it was then heated to expel any CO₂ formed. The excess HCl was titrated to a phenolphthalein end point, it used 37.50 mL of 0.1200 M NaOH. How many moles of HCl was added initially to digest the limestone sample? How many moles of CaCO₃ is present in the limestone sample? What is the purity of the limestone in terms of %w/w CaCO₃?
4. In an experiment to determine the concentration of an HCI sample of unknown concentration, 0.1 M NaOH solution was prepared in the first step. Then, 50 mL of NaOH prepared as 0.1 M and 5 drops of methylorange indicator were added to a 250 mL flask and titrated with H2C204 prepared as 0.05 M. The turning point was observed when 26 mL of H2C204 was consumed in the titration process. In the second step, 50 mL of a non-concentrated HCI solution and 5 drops of phenolphthalein solution were added to a 250 mL flask and titrated with the adjusted NaOH solution. Calculate the concentration of an HCI sample with an unknown concentration, since it is determined that 16 mL of NaOH solution was consumed after titration.
3. Complete neutralization of 10 ml of phosphoric acid solution by NaOH 0.I N in the presence of phenol phthalein until the appearance of purple color (pH, = 9) 11 ml. of NaOH is consumed. (a) What is the concentration of phosphoric acid? (b) Calculate the indicator error. pk2.1 pK. - 7.2 pK - 124