Calculate the ph of a solution prepared by mixing 15.0 ml of 0.10 m naoh and 30.0 ml of a 0.10 m benzoic acid solution. (benzoic acid is monprotic; its dissociation constant is 6.5 x 10^-

Moles = molarity x mass
Moles of NaOH = (0.10 mol/L) (0.015 L) = 0.0015 mol 
Moles of benzoic acid = (0.100 mol/L) (0.0300 L) = 0.003 mol

NaOH and benzoic acid react in a 1:1 molar ratio. This means they are a buffer. 

After the reaction

moles of sodium benzoate = 0.00150 mol 
moles of benzoic acid = 0.00150 mol

pH = pKa + log [base / acid]

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

pH = 4.187

pH = 4.19

Mass is the amount of matter in an object.  weight is the measurement of the pull of gravity on an object.  say for example, you travel to the moon which has a different gravitational field compared to the gravitational field of earth. (gravitational fields: earth = 1, moon = 0.165)  now when you are on the moon, the pull of gravity on you is different than on the earth. and as weight is the measurement of the pull of gravity on an object, that means yes, your weight can and will change on the moon.  however, on the moon, on earth or even on jupiter, the amount of mass inside of you remains the same. meaning your physical mass remains constant.  in conclusion it is possible for your weight to change as your mass remains constant. 

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