Introduction: Solution chemistry has many practical applications in real life. O
ID: 998154 • Letter: I
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Introduction: Solution chemistry has many practical applications in real life. One of the properties studied is colligative properties The prefix coll means to go together. which means that these properties are related to each other Colligative properties are also dependent on the amount of dissolved particles in the solution. These properties include vapor pressure depression. boiling point elevation and freezing point depression. It works as follows: a pure to solvent has a particular boiling point This a the point of the vapor pressure of the liquid is equal to the external pressure which is atmosphere pressure When solute is added it causes the vapor pressure to decrease, in turn this caused the boiling point of the solution to increase and the freeing point to decrease. In the case of making ice cream, adding salt (solute) to the ice causes a vapor pressure decrease which causes a freezing point decrease The solution now has a lower freezing point which causes the ice cream to freeze. Recipe 1/2 cup milk 1/2 tsp vanilla 1 tablespoon sugar 4 cups of crushed ice 1/2 cup softener salt 1 quart size zip-loc bag 1 gallon size Zip loc bag Mix the milk, vanilla and sugar together in the quart site bag. Seal tightly, without any air bubbles Too much air left inside may force the bag open during shaking. Place this bag inside the gallon size bad and fill the bag with 4 cups of crushed ice, than add the salt Again let all the air escape and seal the bag Wrap the bag in the towel or use gloves and shake and massage the bag, making sure the ice surrounds the cream mature Five to eight minutes is adequate time for the mixture to freeze into ice cream. Is the reaction inside the outer bas an endothermic or exothermic reaction? Explain how you know which one It is? After you have made your ice cream, take the temperature of the ice water in the gallon baggle and record the temperature In C. Ideally, how much can a 1.0 m solution of NaCl lower the temperature of the water? Do not forget to multiply the answer by the number of moles of ions. Using the temperature of the salt-water, determine the molality of the salt water in your baggie. WHEN FINISHED. CLEAN UP ANY SPILLS OR MISSES. SAVE THE GALLON BAGGIE AND DRY IT WITH PAPER TOWELS.Explanation / Answer
Number 1: The described method of making ice cream involves using a container within a container. The inner container is filled with the ice-cream mixture and the outer container is filled with crushed ice and salt. The salt makes ice melt, by disrupting hydrogen bonds between water molecules that form the crystal lattice of ice. Melting is an endothermic process during which heat is absorbed. Therefore, melting ice in the ice/salt mixture absorbs the heat from its surroundings, including the ice-cream mixture that gets progressively cooler until it reaches its freezing point. To freeze, a liquid has to give up some of its heat. Because of this freezing is an exothermic change. To summarize, the freezing of ice cream (exothermic change) releases heat that is absorbed (endothermic change) by the melting ice.
Number 3:Solution 1m of NaCl.
According to freezing poin deptression:T = i Kf m
Where i: van 't Hoff factor. Substances which ionize into two ions, like NaCl, have i = 2.
Kf : Cryoscopic constant. For water Kf= 1.86 ºC/m ; "m" is molality (moles of solute/Kg of solvent)
Then T = i Kf m = (2)(1.86ºC/m)(1.0m) = 3.72ºC.
The solution 1.0m can lower 3.72ºC
Number 4: If you got 14.4ºC we can calculate molality "m" using the same equation:
T = i Kf m T=0ºC-(-14.4ºC) = 14.4ºC.
The molality of the salt water is:
m = T/(iKf) = 14.4ºC/2(1.86ºC/m) = 3.87m.
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