Which of the listed reactions evolve a combustible gas...?

Question

Which of the listed reactions evolve a combustible gas...?

$A. magnesium hydroxide + hydrochloric acid .$ $"A. magnesium hydroxide + hydrochloric acid".$
$B. magnesium carbonate + hydrochloric acid .$ $"B. magnesium carbonate + hydrochloric acid".$
$C. magnesium oxide + hydrochloric acid .$ $"C. magnesium oxide + hydrochloric acid".$
$D. magnesium metal + hydrochloric acid .$ $"D. magnesium metal + hydrochloric acid".$

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Answer 1 · 2017-04-02T19:34:23

$Option B$ $"Option B"$

Explanation:

We can write out the individual stoichiometric equations for $A$ $A$ , $B$ $B$ , $C$ $C$ , and $D$ $D$ :

$A:$ $"A:"$

$M {g (O H)}_{2} (s) + 2 H C l (a q) \to M g C l_{2} (a q) + 2 H_{2} O (l)$ $Mg(OH)_2(s) + 2HCl(aq) rarr MgCl_2(aq) + 2H_2O(l)$

$B:$ $"B:"$

$M g C O_{3} (s) + 2 H C l (a q) \to M g C l_{2} (a q) + H_{2} O (l) + C O_{2} (g) ↑ ⏐$ $MgCO_3(s) + 2HCl(aq) rarr MgCl_2(aq) + H_2O(l) +CO_2(g)uarr$

$C:$ $"C:"$

$M g O (s) + 2 H C l (a q) \to M g C l_{2} (a q) + H_{2} O (l)$ $MgO(s) + 2HCl(aq) rarr MgCl_2(aq) + H_2O(l)$

$D:$ $"D:"$

$M g (s) + 2 H C l (a q) \to M g C l_{2} (a q) + H_{2} (g) ↑ ⏐$ $Mg(s) + 2HCl(aq) rarr MgCl_2(aq) + H_2(g)uarr$

At 1st year university level I would expect you to know these reactions. Now ONLY $B$ $"B"$ and $D$ $"D"$ result in gas evolution. However, for $D$ $"D"$ , the gas evolved is dihydrogen, which is certainly combustible:

$H_2(g) + 1/2O_2(g) rarr H_2O(g) + Delta$

And hydrogen gas typically ignites with a pop. On the other hand, the gas evolved in $"B"$ is non-combustible carbon dioxide, which WOULD extinguish a lit taper.

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Which of the listed reactions evolve a combustible gas...?

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