Some Basic Concepts Of Chemistry Question 131
Question: A 0.70 g sample consisting $ CaC _2O _4 $ and $ MgC _2O _4 $ is heated at $ 300{}^\circ C, $ converting the two salts of $ CaCO _3 $ and $ MgCO _3 $ . The sample when weighs 0.47 g. If the sample had been heated to $ 700{}^\circ C $ where the products are CaO and MgO. What would be the weight of mixture of oxides?
Options:
A) 0.36 g
B) 0.14 g
C) 0.28 g
D) 1.08 g
Show Answer
Answer:
Correct Answer: C
Solution:
[c] Idea. While solving this problem, students are advised to use the mole concept and stoichiometry as follows Consider arbitrary mass of $ MgC _2O _4 $ and $ CaC _2O _4(0.7-x) $ and x respectively Write the chemical reaction and calculate weight of both species. Finally using information provided in question complete the further calculation. Let x g = weight of $ CaC _2O _4 $ So, wt. of Mg $ C _2O _4=(0.7-x)g $
$ CaC _2O _4\xrightarrow{\Delta }CaCO _3+CO _2 $
$ MgC _2O _4\xrightarrow{\Delta }MgCO _3+CO _2 $ Weight of $ CaCO _3 $ produced $ =\frac{x}{128}\times 100 $ Weight of $ MgCO _3 $ produced $ =\frac{0.7-x}{112}\times 84 $
$ \frac{x}{128}\times 100+\frac{0.7-x}{112}\times 84=0.47 $
$ x=0.46g $ Mol. wt. $ CaCO _3=100, $ $ MgCO _3=84, $ $ CaC _2O _4=128, $ $ MgC _2O _4=112 $ Due to further heating $ CaCO _3\xrightarrow{\Delta }\underset{\frac{x}{128}}{\mathop{CaO}},+CO _2 $
$ MgCO _3\xrightarrow{\Delta }\underset{\frac{7-x}{112}}{\mathop{MgO}},+CO _2 $ Weight of $ CaO $ and $ MgO $
$ =\frac{0.46}{128}\times 56+\frac{0.24}{112}\times 40 $
$ =0.20+0.0857 $ = 0.28 g
