When dilute hydrochloric acid is added to a solid salt, a gas is evolved with a pungent odor that turns acidified potassium dichromate paper green while a colloidal yellow precipitate of sulfur separates in the reaction vessel. The anion is:
التفسير والحل والبرهان النموذجي: Thiosulfate reacts with dilute HCl to produce SO2 gas and an elemental sulfur yellow colloidal suspension.
2
To distinguish between a white precipitate of barium sulfate (BaSO4) and a white precipitate of barium phosphate (Ba3(PO4)2), one should add:
التفسير والحل والبرهان النموذجي: Barium phosphate is derived from a weaker acid and dissolves in dilute HCl, whereas barium sulfate is completely insoluble in dilute mineral acids.
3
A metal cation that forms a gelatinous white precipitate with NaOH which completely redissolves in excess reagent to form a soluble clear solution is:
التفسير والحل والبرهان النموذجي: Al(OH)3 is an amphoteric hydroxide that reacts with excess NaOH acting as an acid to form soluble NaAlO2.
4
In a titration experiment, 20.0 mL of 0.15 M H2SO4 is completely neutralized by 30.0 mL of NaOH solution. The molar concentration of the NaOH solution is: