Why mg reacts differently in h2o and hcl ( pop tests for both was carried out aswell)

Explanation:

The reaction of magnesium with HCl is as follows -

Mg + HCl > MgCl₂ + H₂

The reaction of magnesium with HCl is as follows -

Mg +  H₂O > Mg ( OH )₂ + H₂

In the above two reactions , hydrogen gas is evolved in both the cases , but in the first reaction , the hydrogen gas is of higher concentration , but in the second reaction the evolved hydrogen is very less , since , the magnesium hydroxide produces will form a protective layer around the magnesium and will prevent the reaction .

and

hence in both the case , the hydrogen produced will be different .

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