Q: "Plan an investigation to show how the concentration of the sodium thiosulfate solution affects the rate of reaction with dilute hydrochloric acid."
Should the substance with the unknown / varying concentration (the alkali) go in the conical flask, and the substance with the fixed concentration (the acid) go in the burette, or vice versa? Does it really matter?
The substance of known concentration goes in the burette, and the substance of unknown concentration goes in the conical flask (plus any indicator, if applicable).