Question

A 1g sample containing CaBr2, Nacl and some inert impurity was dissolved in enough water and treated with excess of aqueous silver nitrate ( AgNO3) where a mixed precipitate of silver chloride (AgCl) and AgBr weighing 1.94g was obtained. Precipitate was washed, dried and shaken with a aqueous solution of NaBr where all AgCl was converted into AgBr. The new precipitate which contain only AgBr weighed to be 2.4g.Mass percentage of CaBr2 and Nacl in the original sample are.........%.. and....... %
.. respectively.

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Answer 1

Answer:The mass of sample is 1.0 g.

The sample is 23% by mass in sodium.

The mass of sodium is  

100

23

​  

×1.0=0.23 g

The atomic masses of Na and Cl are 23.0 g/mol and  35.5 g/ mole.

In NaCl, 0.23 g of Na corresponds to  

23.0

35.5

​  

×0.23=0.355  g of chlorine.

The molar mass of AgCl is 143.5 g/mol and the atomic mass of Cl is 35.5 g/mol.

A 2.0 g precipitate of AgCl separate out.

2.0 g of AgCl corresponds to    

143.5

35.5

​  

×2.0=0.495 g of chlorine.

Out of 0.495 g of chlorine, 0.355 g of chlorine is from NaCl. The remaining 0.495−0.355=0.140 g is from KCl.

The molar mass of KCl is 74.6 g/mol. The atomic mass of chlorine is 35.5 g/mol.

0.140 of chlorine corresponds to    

35.5

74.6

​  

×0.140=0.2928 g of KCl.

Explanation: