You are given an unknown sample that when treated with hydrochloric acid forms a precipitate. After decantation, you add boiling water to the solid; some of the solid disappears. You decant the solution and add a few drops of K2CrO4; a yellow solid appears. To the solid left from the addition of boiling water, you add ammonium hydroxide and centrifuge the product. You then decant the liquid and add concentrated nitric acid to the solution until acidic; a white precipitate forms.

Which group 1 cations were present in your unknown?

Part B : Hg

Part C : Ag

Explanation:

When we added ammonium hydroxide to the solid remains after addition hot water , AgCl dissolve due to the formation of soluble complex [Ag(NH3)2]+ and Hg2Cl2 gives black precipitate with ammonium hydroxide due to formation of elemental mercury.

Black precipitate is not formed upon addition of amonium hydroxide to the precipitate remains after addition of hot water, so Hg22+ is shown not to be present.

The precepite remains after addition of hot water is dissolved by the addition of ammonium hydroxide, so Ag+ may be present. The presence of Ag+ is not confiremed by K2CrO4 test.

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.