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Q.Carnallite is a double chloride of potassium and magnesium containing 38.86% of...

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user8235304 | Student, Grade 11 | (Level 1) Valedictorian

Posted July 10, 2013 at 5:49 PM via web

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Q.Carnallite is a double chloride of potassium and magnesium containing 38.86% of water.0.458 g of it gve 0.71 g of `AgCl`  and 0.666 g of it gave 0.27 g `Mg_2P_2O_7` .Find the percentage of `KCl` in the carnallite.

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justaguide | College Teacher | (Level 2) Distinguished Educator

Posted July 10, 2013 at 6:26 PM (Answer #1)

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Carnallite is a compound containing potassium chloride KCl,  magnesium chloride `MgCl_2` and water. The percentage of water is 38.86.

0.458 g of carnallite gives 0.71 g of AgCl. 0.71 g of AgCl has `0.71*(35.45/143.32)` g of chlorine. This gives the percentage of chlorine in carnallite as `(0.71*(35.45/143.32))/0.458*100` = 38.34

2 atoms of the chloride constitute the chlorine in the molecule of `MgCl_2` and one atom of chlorine builds the KCl molecule. The mass of potassium and magnesium in carnallite is 100 - 38.34 - 38.86 = 22.8%. The percentage mass of potassium is `(130/211)*22.8` = 14.047% 

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