1) A sample of 0.5843 g of vegetable food was analyzed using the Kjeldahl method to find the nitrogen content. The liberated ammonia is collected in 50.00 mL of 0.1062M hydrochloric acid. The excess acid is titrated using 11.89 mL of 0.0925M NaOH. Calculate the results of this analysis in terms of N%, urea and protein?
2) Titration of the dilute solution of an unknown organic acid with 0.1084 M NaOH consumes 28.62 mL from the base to the phenolphthalein end point. If the sodium salt of an acid is 0.2110 g, what is the molecular mass and formula of this acid?
NH3 + HCl ==> NH4Cl
millimoles HCl initially = mL x M = 50.00 x 0.1062 = 5.310
mmols NaOH to titrate xs = 11.89 x 0.0925 = 1.0998
Subtract 5.310-1.0998 = 4.210 mmols used to neutralize the NH3 liberated in the Kjeldahl process. grams NH3 = mols NH3 x molar mass NH3 0.004210 x 17 = ?
%N = (grams NH3/mas sample)*100 = ?
%protein = %N x factor = ? You need to look up the factor. I think it is 6.89 but you can find it on Google or in your text/notes. For urea the factor is (molar mass N2/molar mass urea)
I don't understand 2. If you titrated the acid where does the Na salt fit in?
To answer question 1, we need to calculate the nitrogen content in the vegetable food, as well as the results in terms of N%, urea, and protein. Let's break down the problem step by step:
Step 1: Calculate the amount of ammonia released
We know that the liberated ammonia is collected in 50.00 mL of 0.1062M hydrochloric acid. Using the relationship between concentration, volume, and moles (n = c x V), we can calculate the moles of ammonia released.
moles of ammonia = concentration of acid x volume of acid
moles of ammonia = 0.1062 mol/L x 0.05000 L
Step 2: Convert moles of ammonia to moles of nitrogen
The Kjeldahl method measures the nitrogen content, so we need to convert the moles of ammonia to moles of nitrogen. Since one molecule of ammonia (NH3) contains one atom of nitrogen, the moles of ammonia and moles of nitrogen are the same.
moles of nitrogen = moles of ammonia
Step 3: Convert moles of nitrogen to grams of nitrogen
The molar mass of nitrogen (N) is approximately 14.01 g/mol. We can use this molar mass to convert moles of nitrogen to grams.
grams of nitrogen = moles of nitrogen x molar mass of nitrogen
grams of nitrogen = moles of nitrogen x 14.01 g/mol
Step 4: Calculate the nitrogen percentage (N%)
Now we have the grams of nitrogen, but we want to express it as a percentage of the total sample weight. To do this, we divide the grams of nitrogen by the sample weight and multiply by 100.
N% = (grams of nitrogen / sample weight) x 100
N% = (grams of nitrogen / 0.5843 g) x 100
Step 5: Calculate urea and protein content
To determine the urea and protein content, we need to use the conversion factors and relationships specific to these substances. The Kjeldahl method assumes that all the nitrogen in the sample is present as urea (NH2CONH2) or protein (which contains 16% nitrogen by weight).
To calculate the urea content, we can use the relationship:
grams of urea = grams of nitrogen x (1 mol of urea / 2 moles of nitrogen) x (molar mass of urea / molar mass of nitrogen)
To calculate the protein content, we can use the relationship:
grams of protein = grams of nitrogen x (1 mol of protein / 0.16 moles of nitrogen) x (molar mass of protein / molar mass of nitrogen)
You would need to know the molar masses of urea and protein to perform these calculations.
To answer question 2, we need to determine the molecular mass and formula of the unknown acid based on the titration with NaOH. Let's break down the problem step by step:
Step 1: Calculate the moles of NaOH used
We know that the volume of NaOH used is 28.62 mL and the concentration of NaOH is 0.1084 M. Using the relationship between concentration, volume, and moles (n = c x V), we can calculate the moles of NaOH used.
moles of NaOH = concentration of NaOH x volume of NaOH
moles of NaOH = 0.1084 mol/L x 0.02862 L
Step 2: Use the stoichiometry of the acid-base reaction
Since the reaction between the unknown acid and NaOH involves a 1:1 ratio, the number of moles of NaOH used is equal to the number of moles of acid present in the solution.
moles of acid = moles of NaOH
Step 3: Calculate the molar mass of the acid
We know that the mass of the sodium salt of the acid is 0.2110 g. By dividing the mass by the number of moles, we can determine the molar mass of the acid.
molar mass of acid = mass of acid / moles of acid
molar mass of acid = 0.2110 g / moles of acid
Step 4: Determine the formula of the acid
To determine the formula of the acid, we need to know the molar mass and gather additional information. The molar mass will give us the sum of the atomic masses, and based on that, we can derive the empirical formula (the simplest whole number ratio of atoms in the compound).
Please provide additional information or follow-up questions to proceed with finding the molecular formula of the acid.