A solution contains 25.0 g of KOH per liter. Calculate the pOH of the solution.

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Explanation / Answer

KOH is a strong base, so it will dissociate completely intoOH- and K+: KOH --> OH- + K+ This means that the concentration of KOH reacted will equal theconcentration of OH- produced. The concentration ofOH- can then be used to determine the pOH of thesolution. First, it is necessary to determine the concentration, or themolarity, of the solution: Molarity=moles solute/liters solution If it is 25.0 g KOH per liter, then there is one liter of solution.Unfortunately, grams KOH must be converted to moles for themolarity equation. This can be done using the molar mass of KOH toconvert from grams to moles: Molar Mass of KOH = (K: 1 x 39.10g) + (O: 1 x 16.00g ) + (H: 1 x1.01g)       = 56.11 g/mol Moles of KOH= 25.0g KOH x 1 molKOH                                                  56.11g KOH The calculated moles of KOH can then be plugged into the molarityequation along with the 1 L of solution: Molarity = Calculated moles / 1 L This will give you the concentration of the KOH, which asdetermined previously, will be the concentration of theOH-. The OH- concentration can then be used to determine thepOH of the solution using: pOH= -log [OH-] (brackets indicate "concentration of")

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