07 chem ce #17 @ thhzpvx的部落格

標題:

07 chem ce #17

發問:

20cm^2 of calcium chloride solution contains 1.0 x 10^-2 moles ofCl-(ag) ions.What is the molarity of the solution? A. 1.0 x 10-4M B. 2.5 x 10-4M C. 2.5 x 10-1M D. 5.0 x 10-1M ANS:C 我想知道點解no. of mole of thecompound in the solution = 1.0 X 10-2 / 2 = 5 X 10-3 mol,唔係好明點解要除2,請幫忙解一解!!!!@.@ 更新: 咁係唔係即係話要搵solution既molarity,就一定要將Ca同Cl 既 mole ratio 變成一樣?

最佳解答:

Note that the chemical formula of calcium chloride is CaCl2. So, For one CaCl2 compound molecule, there should be 2 Cl- ions. For the solution contains 1.0 X 10^-2 moles of Cl- (aq) ions, there should be (1.0 X 10^-2) / 2 = 5 X 10^-3 moles of the compound in aqueous form. By molarity = no. of mole / volume = (5 X 10^-3)(0.020) = 0.25 M = 2.5 X 10^-1 M. Ans: C 2009-03-06 07:33:18 補充：不是，而是要找出它們的molar ratio。