A. How many moles of Nitrogen should 1.0 L of Stock solution contain? B. How man

Question

A. How many moles of Nitrogen should 1.0 L of Stock solution contain?

B. How many moles of KNO3 should 1.0 L of stock solution contain?

C. How many grams of KNO3 will you have to weigh out to prepare 1.0 L of stock solution? (Show ALL work!) (Reminder: the concentration of stock must be known to 3 significant figures!)

2. Another Stock solution you may have to prepare must contain 80.0 mg Phosphorus /L. Using steps similar to those used for Nitrogen Stock solution in Question 1, find how many grams of Potassuim Dihydrogen Phosphate (KH2PO4 ) you will need to weigh out to prepare 1.0 L of such Stock solution

Explanation / Answer

1)

concentration of KNO3 = concentration of N (as there is only one mole of N in one mole of KNO3)

A) concentration of N = 150 mg N/L

B) moles of KNO3 = 150 * 10^-3 / 101

= 0.00148 moles = 1.48 milimoles

C) 150 mg

2) moles of Phosphorous = 80 / 31

= 2.58 milimoles

now, there is one mole of Phosphorous in one mole of KH2PO4

:. moles of KH2PO4 = 2.58 milimoles

:. weight of KH2PO4 required = 2.58 * 136 mg

= 350.88 mg

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