The Kjeldahl procedure was used to analyze 256 µL of a solution containing 37.9 mg protein/mL. The liberated NH₃ was collected in 5.00 mL of 0.0336 M HCl, and the remaining acid required 6.34 mL of 0.010 M NaOH for complete titration.

What is the weight percent of N in the protein?

Please show step by step.

To calculate the weight percent of N in the protein, you need to determine the amount of N in the solution and the mass of protein. Follow the step-by-step explanation to calculate the weight percent of N.

Explanation:

To calculate the weight percent of N in the protein, we need to determine the amount of N in the solution and the mass of protein.

Step 1: Calculate the amount of N in the solution.

To do this, we need to determine the moles of N in the liberated NH3 collected in the HCl solution.

The volume of HCl solution is 5.00 mL, and the concentration of HCl is 0.0336 M. We can use the formula C1V1 = C2V2 to calculate the moles of NH3:

(0.0336 M)(0.00500 L) = (moles of NH3)(0.00100 L)

(moles of NH3) = 0.0336 x 0.00500 / 0.00100 = 0.168 mol NH3

Since each mol of NH3 is generated from 1 mol of N in the protein, there are 0.168 mol of N in the solution.

Step 2: Calculate the mass of protein in the solution.

To do this, we need to determine the moles of NaOH that neutralize the remaining acid.

The volume of NaOH solution is 6.34 mL, and the concentration of NaOH is 0.010 M. We can use the formula C1V1 = C2V2 to calculate the moles of NaOH:

(0.010 M)(0.00634 L) = (moles of NaOH)(0.00100 L)

(moles of NaOH) = 0.010 x 0.00634 / 0.00100 = 0.0634 mol NaOH

Since each mol of NaOH neutralizes 1 mol of acid, there were 0.0634 mol of acid in the solution.

Since the moles of acid in the remaining acid are equal to the moles of acid in the liberated NH3, there were 0.168 mol of acid in the solution before neutralization.

Thus, there were 0.168 mol of protein in the solution.

Step 3: Calculate the weight percent of N in the protein.

The weight percent of N is calculated using the formula:

Weight percent of N = (mass of N in protein / mass of protein) x 100%

To calculate the mass of protein, we need to convert the volume of the solution to grams:

Mass of protein = (volume of solution)(concentration of protein)

= (256 uL / 1000)(37.9 mg/mL)

= 9.70 mg

Now we can calculate the weight percent of N:

Weight percent of N = (0.168 mol N) / (0.00970 g protein) x 100% = 1.73%