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The information:
An unidentified acid with a concentration of 1.0 mol/L has been given to you to
identify. The acid appears in your data booklet on the Relative Strengths of Acids
and Bases table. The following test results were recorded:

1. Methyl violet is yellow when added to the acid.
2. The acid did not form a precipitate when a solution containing Ag + (aq) was
added to it.
3. The solution turned blue and a gas was formed when a strip of copper was
added to the acid.

The question:
Based on these test results, identify the acid and justify your choice. Your answer
should include equations and/or calculations where appropriate.

My question:
How do I go about doing this? I really have no idea! Please help!

1) the color of the indicator tells you it has a very low pH, indicating a strong acid.
2) No precipate..not HCl, nor H2SO4...silver sulfate is slightly soluble, no way a 1M solution would be soluble.
3) OK, now of the three common strong acids, HCl, H2SO4, and HNO3, which will leave a blue solution with a gas (not hydrogen) being released when copper is in acid?

I agree that it PROBABLY is HNO3.
AgBr, AgCl, and AgI are insoluble so that eliminates HCl, HI, and HBr. Ag2SO4 is only slightly soluble but I rule that out, also, because H2SO4 reacts with Cu but only if the solution is hot (SO2 is given off and blue CuSO4 is formed). AgClO4 is freely soluble and AgClO3 rather soluble but HClO3 and HClO4 are not common acids; therefore, I eliminate those but they could be possibilities because there is no mention of the color of the gas (hydrogen is colorless and odorless). That leaves only the one common strong acid, HNO3. It would have been nice to say that the gas emitted was not colorless or that it was not odorless (that would have positively eliminated HClO4 and HClO3. I hope this helps. Post the balanced equations if you would like for us to check them for you.

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