3. Using a singlereagentand only reaction chemistry that was partofthis experime

Question

3. Using a singlereagentand only reaction chemistry that was partofthis experiment. how could you distinguish between the following pairs ofsubstances contained in separate test tubes? Explain in words how you could tell, and give the net-ionic equation for any reaction that occurs in the test. a. Hg,(NO, 2 and Mg(NO, 2 solutions Reagent: b, Hg,Cl, and AgCl solids Reagent: c. Na Cro, and HCl solutions Reagent 4. A student has an unknown solution that can contain any combination of Group I cations. A white precipitate (P1) forms when excess 6 M HCI is added to the unknown. After discarding the supernate (si), hot water is added to the precipitate (P1) and the mixture boiled for 5 minutes After removing the mixture from the hot water bath, it is left at room temperature for 10 minutes before centrifuging and removing the supernate (S2) from the precipitate (P2). S2 gives no precipitate when 1 M KrCro is added. When 15 M NH, is added to P2 a black precipitate forms. Complete the following table. For each cation, put a check mark to indicate whether the descrip allows you to say that the cation is definitely tion present, definitely absent, or possibly present or absent. Possibly Present Absent or Absent

Explanation / Answer

a)

Note that Hg+2 ions will precipitate as Cl- ions are aded, MgCl2 is solbule, so HgCl2 precipitates

b)

First add Cl- ions

Forms

Hg2Cl2 and AgCl

Addition of NH3 in order to increas pH

[Ag(NH3)2]+(aq) + 2 H3O+(aq) + Cl–(aq) AgCl(s) + 2 NH4 +(aq) + 2 H2O(liq)

Hg2+(aq) + NH3(aq) + Cl–(aq) + H2O(liq) HgClNH2(s) + H3O+(aq)

this way you can separate them

c)

HCl --> pH will be acidic,add any base and this should react, release of energy expected

for

Na2CrO4, this is a base, since CrO4- can accpet H+, pH must be basic, addition of H+ should absorb energy

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