that a \( 0.5136-\mathrm{g} \) sample required \( 48.13 \mathrm{~mL} \) of \( 0.1251 \mathrm{M} \mathrm{NaOH} \). Soal 2 The amount of protein in a sample of cheese is determined by a Kjeldahl analysis for nitrogen. After digesting a \( 0.9814-\mathrm{g} \) sample of cheese, the nitrogen is oxidized to \( \mathrm{NH}_{4}{ }^{+} \), converted to \( \mathrm{NH}_{3} \) with \( \mathrm{NaOH} \), and distilled into a collection flask containing \( 50.00 \mathrm{~mL} \) of \( 0.1047 \mathrm{M} \mathrm{HCl} \). The excess \( \mathrm{HCl} \) is then back titrated with \( 0.1183 \mathrm{M} \mathrm{NaOH} \), requiring \( 22.84 \mathrm{~mL} \) to reach the bromothymol blue end point. Report the \%w/w protein in the cheese given that there is \( 6.38 \mathrm{~g} \) of protein for every gram of nitrogen in most dairy products. Soal 3 'The alkalinity of natural waters is usually controlled by \( \mathrm{OH}^{-}, \mathrm{CO}_{3}{ }^{2-} \), and \( \mathrm{HCO}_{3^{-}}{ }^{-} \), which may be present singularly or in combination. Titrating a
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Moles of HCl = Molarity * Volume = 0.1047 M * 50.00 mL = 5.235 mmol Show more…
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The Kjeldahl method is used in agricultural chemistry to determine the percent protein in natural products. The method is based on converting all the protein nitrogen to ammonia and then determining the amount of ammonia by titration. The percent nitrogen in the sample under analysis can be calculated from the quantity of ammonia produced. Interestingly, the majority of protein molecules in living matter contain just about $16 \%$ nitrogen. A 1.250 g sample of meat is heated with concentrated sulfuric acid and a catalyst to convert all the nitrogen in the meat to $\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4} .$ Then excess $\mathrm{NaOH}(\mathrm{aq})$ is added to the mixture, which is heated to expel $\mathrm{NH}_{3}(\mathrm{g}) .$ All the nitrogen from the sample is found in the $\mathrm{NH}_{3}(\mathrm{g}),$ which is then absorbed in and neutralized by $50.00 \mathrm{mL}$ of dilute $\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) .$ The excess $\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq})$ requires $32.24 \mathrm{mL}$ of $0.4498 \mathrm{M}$ NaOH for its titration. A separate 25.00 mL sample of the dilute $\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq})$ requires $22.24 \mathrm{mL}$ of $0.4498 \mathrm{M}$ NaOH for its titration. What is the percent protein in the meat?
A 2.00 mL sample of serum is analyzed for protein by the modified Kjeldahl method. The sample is digested, and the resulting ammonia is distilled into a boric acid solution, consuming 15.0 mL of standard HCl to titrate the ammonium borate. HCl is standardized by treating 0.330 g of pure (NH4)2SO4 in the same way. If 33.3 mL of acid is consumed in the standardization titration, what is the serum protein concentration in g% (weight/vol)?
Dinesh S.
In one of Fritz Haber's experiments to establish the conditions required for the ammonia synthesis reaction, pure $\mathrm{NH}_{3}(\mathrm{g})$ was passed over an iron catalyst at $901^{\circ} \mathrm{C}$ and 30.0 atm. The gas leaving the reactor was bubbled through $20.00 \mathrm{mL}$ of a $\mathrm{HCl}($ aq) solution. In this way, the $\mathrm{NH}_{3}(\mathrm{g})$ present was removed by reaction with HCl. The remaining gas occupied a volume of $1.82 \mathrm{L}$ at $0^{\circ} \mathrm{C}$ and 1.00 atm. The $20.00 \mathrm{mL}$ of $\mathrm{HCl}(\mathrm{aq})$ through which the gas had been bubbled required $15.42 \mathrm{mL}$ of $0.0523 \mathrm{M} \mathrm{KOH}$ for its titration. Another $20.00 \mathrm{mL}$ sample of the same $\mathrm{HCl}(\mathrm{aq})$ through which no gas had been bubbled required $18.72 \mathrm{mL}$ of $0.0523 \mathrm{M}$ KOH for its titration. Use these data to obtain a value of $K_{p}$ at $901^{\circ} \mathrm{C}$ for the reaction $\mathrm{N}_{2}(\mathrm{g})+3 \mathrm{H}_{2}(\mathrm{g}) \rightleftharpoons$ $2 \mathrm{NH}_{3}(\mathrm{g})$
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