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Decomposition of Carbonates watch

1. Q: Equal masses of barium carbonate and magnesium carbonate powders are mixed together. The mixture is then heated using a Bunsen burner flame until there is no further change. A gas is given off. Which statements are correct?
1) The residue left after heating reacts with aqueous hydrochloric acid to produce carbon dioxide.
2) The percentage decrease in mass after heating is 26% (to 2 significant figures).
3) The gas given off during heating relights a glowing splint.

Is this question referring to the decomposition of the two carbonates? If so, shouldn't the residue produce MgCl2, BaCl2 and H20 with the reaction with HCl, since MgO and BaO were produced after decomposition? I also couldn't calculate the precentage decrease when using the formula for decomposition.

The answer is 1) and 2).
2. (Original post by sourmango1)
Q: Equal masses of barium carbonate and magnesium carbonate powders are mixed together. The mixture is then heated using a Bunsen burner flame until there is no further change. A gas is given off. Which statements are correct?
1) The residue left after heating reacts with aqueous hydrochloric acid to produce carbon dioxide.
2) The percentage decrease in mass after heating is 26% (to 2 significant figures).
3) The gas given off during heating relights a glowing splint.

Is this question referring to the decomposition of the two carbonates? If so, shouldn't the residue produce MgCl2, BaCl2 and H20 with the reaction with HCl, since MgO and BaO were produced after decomposition? I also couldn't calculate the precentage decrease when using the formula for decomposition.

The answer is 1) and 2).
I really do not like this question as it seems to suggest that barium carbonate is stable to heat, when this is not the case.

1. The fact that some carbon dioxde is produced when the residue is treated with acid means that there is a carbonate present.

2. If 50% of the mixture is magnesium carbonate (relative mass = 84) and it decomposes to MgO (relative mass 40), then the 50% loses 44/84 x 100 % of its mass = 52.4%
so the mass loss of the 100% mixture = 26.2%

BUT, this assumes that barium carbonate does not decompose on heating.
3. (Original post by charco)
I really do not like this question as it seems to suggest that barium carbonate is stable to heat, when this is not the case.

1. The fact that some carbon dioxde is produced when the residue is treated with acid means that there is a carbonate present.

2. If 50% of the mixture is magnesium carbonate (relative mass = 84) and it decomposes to MgO (relative mass 40), then the 50% loses 44/84 x 100 % of its mass = 52.4%
so the mass loss of the 100% mixture = 26.2%

BUT, this assumes that barium carbonate does not decompose on heating.
Ah, I see, so barium carbonate did not decompose at all, which explains the acid observation. Thanks a lot.

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