Help. Chem. We did a laboratory experiment where we had to find the anion and ca

Question

Help. Chem.

We did a laboratory experiment where we had to find the anion and cation of an unknown substance.

The last step for anion:

We poured half a spatula of the unknown substance (analyte) into a clean test tube, then added 2 mL of HCl at 4,0 M and a drop of BaCl2. The solution turned yellow, we had to perform centrifugation for 5 minutes. A white precipitate was formed, which means that the anion is either SO4 or HSO4.

To find whether the anion was SO4or HSO4, we had to measure the PH value of a mixture of water and half a spatula of the the unknown chemical substance. The pH value read acid (0-1) which means that the anion is HSO4. However, we were told that the result was wrong, and that it was supposed to be SO4.

anion: SO4

The last step for cation:

We poured half a spatula of the same unknown substance (analyte) into a clean test tube, then added 2 mL of HCl at molar concentration 4,0 M and a drop of K4[Fe(CN)6]. The solution turned blue, which means that the cation is Fe+++.

What is the unknown substance and its molar concentration?

Explanation / Answer

if pH is too low, that is, 0-1 it is not likely that HSO4 is present, sinceHSO4 is strong acid and you will have must likely, in low pH: HSO4- = H+ + SO4-2 ionization

for last step:

This if Fe+3 due to the Fe test

so

Fe+3 and SO4-2 will form:

Fe2(SO4)3 which is Iron(III) Sulfate

Concentration can't be calcualted since no volume of sample is stated

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