# Chemical Forums

## Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: daigo1 on March 02, 2013, 11:20:34 AM

Title: Weight loss by decomposition
Post by: daigo1 on March 02, 2013, 11:20:34 AM
Given the reaction: $$2LiHCO_3 + SiO_2 \rightarrow Li_{2}CO_3 + SiO_2 + CO_2 + H_{2}O$$ where $$SiO_2$$ is unaffected, the mass of the $$2LiHCO_3 + SiO_2$$ is 9.62 g. and $$Li_{2}CO_3 + SiO_2$$ is 6.85 g., find:

a) mass loss due to $$CO_2 + H_{2}O$$
b) mass of $$LiHCO_3$$ in the original mixture
c) mass of $$SiO_2$$ in the new mixture

a)The mass lost is just 9.62 g. - 6.85 g. = 2.77 g. of $$CO_2 + H_{2}O$$

b) For every 136 g. of $$LiHCO_3$$, 62 g. are lost to $$CO_2 + H_{2}O$$. So if 2.77 g. are lost to $$CO_2 + H_{2}O$$, then there was initially 0.79 g. of $$LiHCO_3$$

c) Since the mass of $$SiO_2$$ does not change, 9.62 g. in the original - 0.79 g. of $$LiHCO_3$$ = 8.83 g. $$SiO_2$$. But 8.83 g. of $$SiO_2$$ + 2.77 g. of $$CO_2 + H_{2}O$$ is greater than 9.62 g. of the original mixture, so mass is not conserved. I don't think this is possible so I don't know what to do
Title: Re: Weight loss by decomposition
Post by: DrCMS on March 02, 2013, 02:04:28 PM

b) For every 136 g. of $$LiHCO_3$$, 62 g. are lost to $$CO_2 + H_{2}O$$. So if 2.77 g. are lost to $$CO_2 + H_{2}O$$, then there was initially 0.79 g. of $$LiHCO_3$$