An equal number of moles of ki and mgi 2 are dissolved in equal volumes of water. which solution has the higher
a. boiling point?
b. vapor pressure?
c. freezing point

Vapor Pressure: Solution containing dissolved KI

Boiling point: Solution containing dissolved MgI₂

Freezing point: Solution containing dissolved KI

Explanation:

Water is a volatile solvent while KI and MgI₂ are non-volatile solute. Addition of non-volatile solute decreases vapor pressure of the pure solvent. This phenomenon is called lowering in vapor pressure.

Lowering in vapor pressure is a colligative property that means lowering in vapor pressure only depends upon the number of solute particles dissolved.

More the number of solute particles, more will be the lowering in the vapor pressure.

Equal number of moles of KI and MgI₂ are added in water. KI dissociates into two ions and MgI₂ dissociates into three ions as follows:

KI ⇒ K⁺ + I⁻

MgI₂ ⇒ Mg²⁺ + 2I⁻

Therefore, more lowering will occur in case of solution of MgI₂.

Hence, KI will have more vapour pressure.

Lowering in vapor pressure causes elevation in boiling point and depression in freezing point and both these are colligative properties.

So, more the number of solute particles, more will be elevation in boiling point and depression in freezing point.

Therefore, solution containing MgI₂ will have more boiling point.

Since, depression in freezing point will occur more in case of solution containing MgI₂, therefore freezing point of solution containing KI will be more.

first, consult an activity series chart to determine if al is more reactive than fe. it is, so it will replace the fe. now, one can continue with the problem.

next, make sure you have a correctly balanced equation.

3feo + 2al ==> 3fe + al2o3

now, determine which reactant (feo or al) is in limiting supply.

moles feo present = 125 g x 1 mole/71.8 g = 1.74 moles

moles al present = 25.0 g x 1 mole/26.98 g = 0.927 moles

since from the balanced equation, it take 3 mol feo for every 2 mol al, al will be limiting.

you can determine this simply by dividing moles of each by their coefficient in the balanced equation. for example: 1.74/3 = 0.58 and 0.927/2 = 0.464. al is less, so it is limiting.

finally, using the stoichiometry in the balanced eq. determine mass of fe that can be produced from 0.927 moles of al.

0.927 moles al x 3 moles fe/2 moles al x 55.8 g/mole = 77.6 g

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