College level question (beware)

PNP (2.8mg) (MW= 140) was dissolved in 20ml of 0.1 M NaOH. A small aliquot of this solution (0.1ml) was diluted with 4.9 ml of pH 8 buffer (0.1M) and the absorbance at 415 was determined. If the molar absorptivity (ɛ) is 15,000L/cm/mol at this wavelength and pH, and the path is 1cm, what reading do you expect?

A = ɛcl
ɛ = M/cm
c= concentration in molarity
l = 1 cm

Question

College level question (beware)

PNP (2.8mg) (MW= 140) was dissolved in 20ml of 0.1 M NaOH. A small aliquot of this solution (0.1ml) was diluted with 4.9 ml of pH 8 buffer (0.1M) and the absorbance at 415 was determined. If the molar absorptivity (ɛ) is 15,000L/cm/mol at this wavelength and pH, and the path is 1cm, what reading do you expect?

A = ɛcl 
ɛ = M/cm
c= concentration in molarity
l = 1 cm

ookawaiioo · Answer

Dont use pKa or the henderson hasselbach equation...... we are looking at ALL concentration of PNP (protonated and ionized form)

anonymous · Answer

What's PNP?  I can't see the relevance of the acid/base issue. Surely the moiety that absorbs in the blue is unlikely to be divided or destroyed by any ordinary acid/base reaction.  Is there any reason to think that the absorption spectrum shifts with pH or soething?  If not...seems to me you should just be able to calculate the final molarity through the double dilution and use Beer's Law with your absorptivity.