Investigating the effects of concentrarion on rate of reaction Add 50 cm3 of dilute sodium thiosulfate solution to a flaskPlace the slask on a piece of paper with a black cross drawn on it. Add 10cm3 of dilute hydrochloric acid to the flask, give the flask a brief swirl to mix the reactants and start the stopwatchWatch the black cross through the flask and time how long it takes to dissapear. Record the results in a tableRepeat the reaction in exactly the same way twice, using the same concentrations of reactantsand calculate a mean time for the cross to dissapearThe reaction can then be repeated with solutions of either reactant at differing concentrations The same person should observe the cross each time