Question

1)what is theoretical absorbance at 340nm wavelength of 10mM solution of NADH (Molar absorbtivity=6330M^-1cm^-1), assuming a path length of 10mm?

2) a bottle of concentrated acid that says 23% by weight, density 1.24g/ml, FW= 19.7. what is the molarity of this acid?

Answer 1

answer: according to Beer's Law

Absorbance = L c

   is not euro its molar absorbtivity = 6330M^-1cm^-1

L is path length = 10mm =1cm

c is concentration= 10mM = 1*10^-2M

Absorbance = 6300 M^-1cm^-1 * 1cm *10^-2M = 63

so theoretical absorbance at 340nm is 63

2) there is a direct formula for molarity calculation when we have given weight% of acids

Molarity = [(%weight * density)/molecular weight] *10

so putting values

molarity = [(23*1.24)/19.7]*10 = 14.47M

formula derivation

molarity = moles of solute/volume of solution(L) = [moles of solute/volume of solution(mL)] *1000

weight% = mass of solute in 100g of solution

23% means 23g in 100 g of solution = 0.23g in 1g of solution

density = massg/volume(mL) = 1.24g/mL means 1.24g is the mass of 1ml solution

so mass of solute = ( 0.23* 1.24) or we can write = ( wt% * density) /100

moles = [(wt% * density) /100 ] / FW