Calculate the normal boiling point of a sample of sea water found to contain $$3.5$$% of NaCl and $$0.13$$% of $$MgCl2$$ by mass. The normal boiling point of water is $$100oC$$ and Kb (water) $$=$$ $$0.51$$ K kg $$mol-1$$. Assume that both the salts are completely ionised

Question

Calculate the normal boiling point of a sample of sea water found to contain $$3.5$$% of NaCl and $$0.13$$% of $$MgCl2$$ by mass. The normal boiling point of water is $$100oC$$ and Kb (water) $$=$$ $$0.51$$ K kg $$mol-1$$. Assume that both the salts are completely ionised

Infinity Learn · Accepted Answer

Mass of NaCl $$=$$ $$3.5$$ gNumber of moles of $$NaCl=3.558.5Number$$ of ions furnished by one molecule of NaCl is $$2$$. So, actual number of moles of particles furnished by sodium chloride $$=2$$×$$3.558.5Similarly$$, actual number of moles of particles furnished by magnesium chloride $$=3$$×$$0.1395Total$$ number of moles of particles $$=(2$$×$$3.558.5+3$$×$$0.1395)=0.1238Mass$$ of water $$=(100$$−$$3.5$$−$$0.13)=96.37$$ $$g=96.371000$$ kgMolality $$=0.123896.37$$×$$1000=1.2846$$Δ$$Tb=Molality$$ ×$$Kb=1.2846$$×$$0.51=0.655$$ KHence, boiling point of sea water $$=$$ $$373.655$$ K or $$100.655oC$$

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