The compound that will have the lowest freezing point when dissolved in water is 1.0M Mg(NO3)2. That is option 3.
Comparing the freezing point of solutions
To compare the freezing points of solution, the total concentration of all the particles when solutes are dissolved in water is determined.
This is an important step to consider because, the greater the concentration of particles, the lower the freezing point will be.
To determine the concentration of all the particles, ionic compounds are alway 2 while covalent compounds are always 1.
- 1.0M NaCl: This compound is ionic (metal with nonmetal), and will dissolve into 2 parts. The total final concentration is (1m)(2)=2m
- 1M NaOH: This compound is ionic and will dissolve into 2 parts. The total final concentration is (1m)(2)=2m.
- 1.0M Mg(NO3)2: This is an ionic compound but contains a polyatomic ions. The total final concentration is 1m(3) = 3m.
- 2M NH3: This is a covalent compound and will remain in a part. The total final concentration is 2m (1)= 2m.
Therefore, since 1.0M Mg(NO3)2 contains the greater concentration of particles, it has lower freezing point.
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