Somewhat confused... my homework is asking me to calculate morality of sodium thiosulfate from a 55 ml solution. the sodium's volume is 50 ml and has a concentration of 0.25M. The rest of the 55ml comes from the 5ml of HCL.

Hey: remember HCl is mostly water.

volume of Solution: .055liters.

you have diluted it 1.1 times. One part stock, .1 added acid solution.

new concentration: .25/1.1 M