Question

Predict the products in the reaction between magnesium and hydrochloric acid. If you were conducting this reaction in the lab, what would be your clue that this was a chemical reaction? If silver replaced magnesium as one of the reactants, what would you expect to happen?

Answer 1

Mg2+ + 2HCl - > MgCl2 + H2
So the reaction between Magnesium and Cloride Acid will resulting Magnesium Cloride and Hydrogen Gas. This is a chemical reaction because Magnesium reacts with Chloride Acid and resulting two different products.
If Magnesium is replaced by Silver
Ag+ + HCl -> AgCl + 1/2H2

Answer 2

Prediction of products:
\[\large\rm Mg_{(s)}+2HCl_{(aq)}-->MgCl_{2(aq)}+H_{2(g)} \]
Clues:
1. Bubbles formed in the solution (due to escape of hydrogen gas)
2. Disappearance of Magnesium metal

Replacing Magnesium with silver
\[\large\rm 2Ag_{(s)}+2HCl_{(aq)}-->2AgCl_{(s)}+H_{2(g)} \]
Expectations:
1. Bubbles formed in the solution (due to escape of hydrogen gas)
2. Disappearance of Silver metal
3. Formation of white precipitate silver chloride