1. Calculate the mass of KH2PO4 required to prepare 100 mL of a solution in whic

Question

1. Calculate the mass of KH2PO4 required to prepare 100 mL of a solution in which the formal concentration of H2PO4- (F(H2PO4-)is 0.20 mol L .

2. Calculate the 2 4 volume of 0.20 mol L KH2PO4 and the volume of 0.10 mol L NaOH required to prepare 50.0 mL of buffer with a formal (or total) concentration of H2PO4- of 0.020 mol - L and a pH = 6.3. Repeat this calculation for buffers (of the same volume and formal -1 concentration) with pH = 6.5, 6.9, 7.5, 7.9, and 8.2. You need only show one sample calculation. You should be able to set up a spreadsheet to do these calculations.

3. When preparing the solutions in the experiment, the protocol requires the bromothymol blue 2 4 solutions be transferred with a pipette. However, the volumes of NaOH and KH PO solutions can be transferred by a graduated cylinder. Why is it not necessary to know these volumes accurately?

Explanation / Answer

Molar mass of KH2PO4 = 136 g/mole

Thus, moles of KH2PO4 required = molaity*volume of solution in litres = 0.2*0.1 = 0.02

Mass of KH2PO4 required = moles*molar mass = 0.02*136 = 2.72 g

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