Hi I'm stuck on these questions can you please help me
A soil sample contains 0.2234 g of Fe3+ per 100g. Fe3+ is precipitated when the soil becomes alkaline as shown in the equation below.
Fe3+ + 3OH- + (x-1)H2O „_ FeOOH.xH2O(s)
This soil is sprayed with 40.0 wt% urea solution with a density of 1.111 g/mL.
Urea decomposition in soil can be given by the following equation.
(H2N)2CO + H2O „_ CO2 + 2NH4+ + 2OH-
(i) Express the concentration of Fe3+ in the soil sample in mmol/g.
(ii) Calculate the mass and the volume of urea solution needed to precipitate all Fe3+ in this soil sample
[Mr (C) = 12.01 g/mol, (H) = 1.007 g/ mol, (O) = 15.99 g/mol, (N) = 14.01 g/ mol, (Fe) = 55.85 g/mol.
Thank you so much
Sarah
Sarah, I read this last night. Truth be know, I really don't understand the problem.
Sure, I can help you with that! Let's go step by step to solve the problem.
(i) Expressing the concentration of Fe3+ in the soil sample in mmol/g:
To do this, we need to calculate the number of moles of Fe3+ in the soil sample and then divide it by the mass of the sample.
1. First, we need to calculate the number of moles of Fe3+ in the sample:
Given:
Mass of Fe3+ = 0.2234 g
Molar mass of Fe3+ = 55.85 g/mol
Number of moles of Fe3+ = Mass of Fe3+ / Molar mass of Fe3+
= 0.2234 g / 55.85 g/mol
2. Now, we need to calculate the mass of the sample in grams:
Given:
Mass of the sample = 100 g
3. Finally, we can express the concentration of Fe3+ in the soil sample in mmol/g:
Concentration of Fe3+ = (Number of moles of Fe3+ / Mass of the sample) * 1000
= ((0.2234 g / 55.85 g/mol) / 100 g) * 1000 mmol/g
(ii) Calculating the mass and volume of urea solution needed to precipitate all Fe3+:
To do this, we need to find the stoichiometry of the reaction and determine the amount of urea solution required to react with all Fe3+.
Given:
Percentage of urea solution = 40.0 wt%
Density of urea solution = 1.111 g/mL
1. First, let's calculate the number of moles of Fe3+ that can be precipitated:
From the balanced equation, we can see that the stoichiometric ratio between Fe3+ and OH- ions is 1:3.
This means that 1 mole of Fe3+ will react with 3 moles of OH-.
Number of moles of Fe3+ = (Number of moles of OH-) / 3
2. Next, we can calculate the number of moles of OH-:
From the balanced equation for urea decomposition, we can see that 1 mole of urea produces 2 moles of OH-.
Given:
Molar mass of urea (H2NCO) = 60.06 g/mol
Number of moles of OH- = (Number of moles of urea) * 2
3. Now, let's find the number of moles of urea required to react with all Fe3+:
From step 1 and step 2, we have:
(Number of moles of urea) = 3 * (Number of moles of Fe3+)
4. Calculate the mass of urea required:
Mass of urea = (Number of moles of urea) * Molar mass of urea
5. Calculate the volume of urea solution required:
Given:
Density of urea solution = 1.111 g/mL
Volume of urea solution = (Mass of urea) / (Density of urea solution)
And there you have it! By following these steps, you can calculate the concentration of Fe3+ in the soil sample and determine the mass and volume of urea solution needed to precipitate all Fe3+ in the soil sample.