F4 chem questions

we shouldn't directly give you answers, but we can give you some hints.

1.
first, calculate no. of mole of ions in each solutions.
for example, no. of mole of nitrate in Ca(NO3)2
= volume x concentration x stoichiometric coefficient = 3 x 0.100 x 2 = 0.6 mole
(coefficient: no. of mole of that ion per mole of the compound; e.g. per mole of Ca(NO3)2 gives 1 mole of calcium and 2 mole of nitrate)
and so on. also note that same ion sums up ---- nitrate is given by both KNO3 and Ca(NO3)2.

then, calculate the final volume of solution mixture.

finally, get the molar concentration = no. of mole / total volume .


2.
many ways to do this, but let's get an easier way: mass percentage of chloride.
as the mass of the salt and the volume of water are the same, mass of chloride is proportional to no. of mole of chloride.

calculate molar mass of these three salts, as well as molar mass of ALL chlorine atoms in it.

NOTE that calcium chloride has TWO mole of chloride per mole of salt; iron(III) chloride has THREE mole of chloride.
NaCl : mass of chloride per mole of salt / mass of salt per mole of salt
= (35.5x1) / (23+35.5) = 60.7%

CaCl2 : (35.5x2) / (40.1+35.5x2) = 63.9%

FeCl3 : (35.5x3) / (55.8+35.5x3) = 65.6%

thus, it's iron(III) chloride producing largest concentration.

NOTE that it's not only molar mass of the salt affects; no. of chloride ion per salt also affects.


2011-03-02 13:16:12 補充：
i gave you answer of Q.2 because it's quite difficult, and tricky to solve.
without actual values, one is not easy to understand.