3. (2 pts) Ten drops of 1.0 M NaCO3 are placed into each of two small test tubes

Question

3. (2 pts) Ten drops of 1.0 M NaCO3 are placed into each of two small test tubes. To the first test tube, 2 drops of 0.1 M Ca(NO3)2 is added, and to the second test tube, 2 drops of 0.1 M Mg(NO3)2 is added. Describe the likely observations for each test tube and state how these results could or could not be used to distinguish between the cations. (2 pts) Six drops of 0.5 M bromine in organic solvent is placed in each of two small test tubes. To the first test tube, 15 drops of 0.1 NaBr is added, and to the second test tube, 15 drops of 0.1 M Nal is added. Descbribe the likely observations for each test tube and state how these results couldbe used to distinguish between the anions.

Explanation / Answer

Q1-.

n = 10 drops

M = 1 Na2CO3

Ca(NO3)2 addition to 1st tube:

Na+ and Ca+2 are presnet as well as NO3- ions

no effect is likely to see

addition of Mg(NO3)2 wil lhave no effect, as well, since Mg+2 will not form any side reaction

The "observations" --> none, solution increase in volume, no visible precipitateion/reaction/gas formation

Q2

Tube 1:

bromine in solvent

NaBr --> aqueous Br- in solution

Br2(l) in orgnaic solvent --> Br2(l) present

note that there will not be reaction, only ionic exhcange between phases i.e. extraction.

No reaction is visible.

Test tube 2:

addition of NaBr --> Brominme will react since aqueous bromiune Br- and organic bromine Br2(l) are present

the other drops contian NaI --> Na+ + I-

recall that

Br2(aq) + 2e- --> 2Br-

I2(aq) + 2e- --> 2I-

since Bromine is much more reactive, then expect

Br2(aq) + 2e- --> 2Br-

2I- --> I2(aq) + 2e-

total addition

Br2(aq) + 2I- --> 2Br- + I2(aq)

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