Calculate the ph of a buffer solution that contains 0.25 m benzoic acid (c6h5co2h) and 0.15m sodium benzoate (c6h5coona). [ka = 6.5 x 10–5 for benzoic acid]

When C6H5COO- is the conjugate base & the C6H5CO2H is the weak acid 

-and we have [C6H5COO-] = 0.15 M

and [C6H5CO2H] = 0.25 M 

- and we have Ka = 6.5 x 10^-5 so, we can use it and get Pka

∴ Pka = -㏒Ka

          = -㏒(6.5 x 10^-5)
          = 4.2

So, by using H-H equation:

PH = Pka + ㏒[C6H5COO-]/[C6H5CO2H]

     = 4.2 + (0.15 / 0.25)

     = 4.8

The independent variable is the type of music.the dependent variable is the pulse rate.the intervening variable is the age of the subject.if the mother does not like rock, her pulse is likely to not increase.the same might be true for the sister.the friend may like rap and gets excited.to establish cause/effect relationship, all of the subjects must be consistent.hope i .