prepare a .1 normal solution of sod.hydroxide by dissolving 4 g in 100ml distilled water and prepare .1 normal oxalic acid soln by dissolving 4.5g of dehydrated or6.3 of dihydrated oxalic acid and make volume upto 100ml,standardise base by using phenolphthalein indicator and it is your primary standard ,now use it to standardise your acid.