[victorjj]

hi everybody , i'm a student at high school in france.
i have to make a presentation with congo red in english.so .. i need your help ...please !
i just want to know which results will be given with the followed tests:

the first tube we have congo red solution (10 exponent minus 3 mol/L) with 4 mL of water , and we add a few drop of a hydrochloric acid solution . which color can we obtain ? (i thought that it will give blue , but i'm not sure of this result,congo red gives the color blue when the solution is acidic ?)
and the second tube we make the same experience with caustic soda solution instead of hydrochloric acid solution. which color can we obtain ? (i think red ? because the caustic soda is basic?)

and last experience we pour 100 mL of plain water , we add 1 ml of 10 percent sodium carbonate solution , 1ml of 10 percent sodium sulphate solution. and we add a little of congo red solution , and then we immerse the samples of fabric made of cotton nylon and wool in this solution , we let this solution boil in bain marie for ten minutes , what are we going to obtained ?? (we did this experience but i forgot this result ....so if someone know it , please tell me..)

and few another questions whichs i'm searching for answers : what is a direct colouring ? and why and how does congo red change its colour with pH ?
thank you very much , if you can not answer to all the questions , no matter , i'm searching for it too on the web and in the book . so thank onece more . i'm waiting for your answers !
 

[Borek]

http://www.titrations.info/acid-base-titration-indicators-preparation#congo-red