need to calculate the mass (m ) of NaoH with C% = 15 % , to balance 176 g of H2SO4 so i though to use this method C% = mass of h2s04 / mass of h2so4 + mass of Naoh which is unknown mass of Naoh = c% x mass of h2so4 / 100 is this the right method or not ?
I can't follow your thought, mostly because I don't know the definition of your terms, principally C%. The second question I have is about the 15%. Is that 15% w/w or w/v? Third, you don't have a volume of NaOH being added and you don't need one if you are just looking for the mass. Use stoichiometry to solve your problem.
First you should write and balance the equation.
2NaOH + H2SO4 ==> 2H2O + Na2SO4