You want to determine the protein content in milk with the Kjeldahl method. You take 100 g whole milk and use 100 mL of 0.5 M hydrochloric acid to collect ammonia. You needed 34.50 mL of 0.3512 M NaOH for the back-titration. Calculate the percentage of protein in the sample where CP = 6.38 (that is % protein = CP x %N).

3.38%

Explanation:

Given that;

the mass of the whole milk sample = 100 g

volume of HCl = 100 mL = 0.1 L

molarity of HCl = 0.5 M

volume of NaOH = 34.50 mL = 0.0345 L

molarity of NaOH = 0.3512 M

Since we knew the molarity and volume of both HCl and NaOH; we can calculate their corresponding number of moles present.

So, number of moles of HCl = molarity of HCl × volume of HCl

number of moles of HCl = 0.5 M ×  0.100 mL

                                        = 0.05 mole

number of moles of NaOH = Molarity of NaOH ×  Volume of NaOH

number of moles of NaOH = 0.3512 M ×  0.0345 L

                                            = 0.012 mole

From the question, we can deduce that the number of HCl that is consumed by NH₃ is equal to the number of moles of HCl that is consumed by NaOH.

SO, number of moles of HCl consumed by NH₃ = Total moles of HCl - moles of HCl consumed by NaOH

= 0.05 mole - 0.012 mole

= 0.038 mole

However, to determine the mole of NH₃ present , we have:

number of moles of NH₃ present = number of moles of HCl consumed by NH₃  = 0.038

∴ the mass of Nitrogen with the molecular weight (14.0 g/mol) = 0.038 moles × 14.0 g/mol

= 0.530 g

Now, the percentage of Nitrogen can be calculated as;

%

the percentage of protein in the sample = CP × %age of N

where CP is given as 6.38

∴ the percentage of protein in the sample = 6.38 ×  0.530%

the percentage of protein in the sample = 3.3814%

the percentage of protein in the sample = 3.38%

each  column  of the  table  is called a group. elements in a group share similar properties. groups are  read  from  top  to  bottom. metal. metalloid. nonmetal. solid. liquid. gas. fe. hg. o.  2. 3. 4. 5. 6. 7. 8. 9.  2. beryllium. 9.012. 4.  sodium. 22.990.  11. 3.  magnesium. 24.305.  12.  potassium. 39.098.  19. 4.  calcium. 40.078.  20. i guess  i