Determine the volume in milliliters of 0.400 M MgSO_4 solution that must be adde

Question

Determine the volume in milliliters of 0.400 M MgSO_4 solution that must be added to completely react with 0.02591 moles of phosphorus present in a fertilizer sample. At each point in the procedure, you are striving to maximize the amount of phosphorus recovered from the fertilizer. Which of the procedural steps below will NOT improve your recovery of phosphorus? Allow the mixture of MgSO_4 solution and fertilizer filtrate to stand in an ice bath for 30 minutes. Add 50% more of the calculated amount of MgSO_4 solution to the water soluble components of the fertilizer. Test the pH of the mixture of MgSO_4 solution and fertilizer filtrate and. if necessary, add ammonia until the pH is at least 9. Rinse the precipitate with deionized water and set it to dry. Indicate whether each of the following experimental difficulties will lead to an artificially high or an artificially low value in the mass of phosphorus recovered.

Explanation / Answer

Question 4

We must know that phosphorus is present in fertilizers in the form of phosphates (PO43-)

So now we have the following reaction taking place

3MgSO4 + 2PO43- -----------> Mg3(PO4)2 + 3SO4-2

This is the balanced reaction that will happen. So we see here that 3 moles of 3MgSO4 react with 2 mole of phosphorus compound.

Let volume of MgSO4 added =X mL

Molarity of MgSO4 = 0.4

Moles of MgSO4 =M* V = 0.4X

Moles of Phosphorus = 0.02591

Therefore

Moles of MgSO4 /Moles of Phosphorus = 3/2

SO Moles of MgSO4 =(3/2)* Moles of Phosphorus = 1.5 * 0.02591=0.0388

So 0.4X = 0.0388

x =0.0388/4 = 0.0097 L = 9.7 mL

Therefore volume of MgSO4 solution added for complete reaction with phosphorus = 9.7 mL

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