標題:
chemical calculation(molar mass)
發問:
A hydrated salt contains 10 moles of water of crystallization per mole of crystals and the percentage by mass of anhydrous salt is 37.06.Find the molar mass of the hydrated salt.Answer:286 gi've tried to calculate and get the right answer by 1__________ 0.06294/18but i don'n... 顯示更多 A hydrated salt contains 10 moles of water of crystallization per mole of crystals and the percentage by mass of anhydrous salt is 37.06.Find the molar mass of the hydrated salt. Answer:286 g i've tried to calculate and get the right answer by 1 __________ 0.06294/18 but i don'n know the reason at all. PLZ help me
最佳解答:
Let the molar mass of the hydrated salt be m g. % by mass of water = 100% - 37.06% = 62.94% Consider the water of crystallization, Mass / Molar mass = No. of moles ( m )( 62.94% ) / ( 2 + 16 ) = 10 m = 286g ( 3 s.f. ) 2008-06-09 18:36:09 補充： From the given, the % by mass of water is 62.94%. Then the molar mass of water is 18g. As there are 10 moles of water of crystallization per mole of crystals, you can find the molar mass of the hydrated salt as above. 2008-06-09 19:08:21 補充： I think the below's answer is not so accurate, as it is not given that [molar ratio of the anhydrous salt to water = 1 : 10 ]. Though the same answer is reached, it is not a proper way to assume sth that might not be true. 2008-06-13 15:28:12 補充： 我覺得002的做法是把一些題目沒有提及的條件假設了( molar ratio of the anhydrous salt to water = 1 : 10 ), 雖然一般情況下這都是正確, 但這並不是最準確的做法。
其他解答:
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其實 001 同 002 兩個答案的做法都是對的，雖然表面看來不一樣，但其實是同一方法，表達有異而已。若果是我，除非後來的答案特別好，否則我會選一個回答得較早的答案。|||||let X be the molar mass of the hydrated salt. the mass ratio of the anhydrous salt to water =37.06: 62.94 the molar ratio of the anhydrous salt to water =1:10 but it also equal to 37.06/(X-180): 62.94/18 so 62.94/18=10x37.06/(X-180) 62.94(X-180)= 180x37.06 X-180=106 X=286g
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