I am a graduate student in civil engineering (focus in structural and materials). Research I am doing involves the NCHRP Report 244 Series II tests, for background. I have not had any trouble with this standard except for the procedure section:
"slowly add 25mL of dilute (1+1) nitric acid, breaking up any lumps with a glass rod. . . Add 3 drops of methyl orange indicator and stir. Cover the beaker with a watch glass and allow to stand for 1 to 2 min. If a yellow to yellow-orange color appears on top of the settled solids, the solution is not sufficiently acidic. Add additional dilute nitric acid dropwise while stirring until a faint pink or red color persists. Then add 1- drops in excess. Heat the covered beaker rapidly to boiling. ..."
I get the pink color to persist initially for 10 to 15 seconds. Then it is dispersed by the turbid powder slurry. Is this normal? Even after nearly double the amount of nitric acid specified, I get the same effect.
Multiple samples I have ran the process to finish, and all are using way more silver nitrate than what they should be using. I feel like this isn't right, especially that the theoretical amount of chlorides obtained are not high. I feel like my error is coming from the acid digestion/ bringing to rapid boil phase. Could anyone offer any pragmatic advice or solution?
thanks!
"slowly add 25mL of dilute (1+1) nitric acid, breaking up any lumps with a glass rod. . . Add 3 drops of methyl orange indicator and stir. Cover the beaker with a watch glass and allow to stand for 1 to 2 min. If a yellow to yellow-orange color appears on top of the settled solids, the solution is not sufficiently acidic. Add additional dilute nitric acid dropwise while stirring until a faint pink or red color persists. Then add 1- drops in excess. Heat the covered beaker rapidly to boiling. ..."
I get the pink color to persist initially for 10 to 15 seconds. Then it is dispersed by the turbid powder slurry. Is this normal? Even after nearly double the amount of nitric acid specified, I get the same effect.
Multiple samples I have ran the process to finish, and all are using way more silver nitrate than what they should be using. I feel like this isn't right, especially that the theoretical amount of chlorides obtained are not high. I feel like my error is coming from the acid digestion/ bringing to rapid boil phase. Could anyone offer any pragmatic advice or solution?
thanks!
