PERTEMUAN_14. Using English to report

 Practical Chemistry Report of Decreasing Freezing Point A Solution

Chemical Practicum Report

Decrease of Freezing Point A Solution

A. Test Topics

Colligative nature.

B. Purpose of Experiment

Determine the reduction of freezing point of a solution.

C. Basic Theory

The freezing point is the temperature at which the vapor pressure of the liquid is equal to the vapor pressure in a solid state. The freezing point of the solution is lower than the freezing point of pure solvent. In freezing a solution, the freezing is solely the solvent, while the solute does not freeze. The freezing point is a fixed temperature in which an appropriate substance changes from a liquid to a solid state. Every substance that has freezing has a pressure of 1 atm.

The freezing point of a liquid will change if the vapor pressure changes, usually caused by the introduction of a solute or in other words, if the liquid is not pure, the freezing point changes (the freezing point will decrease).

The presence of solute causes a more difficult solvent to freeze, consequently the freezing point of the solution will be lower than the freezing point of the pure solvent. The difference between the freezing point of the solution and the freezing point of the pure solvent is called the decrease of the freezing point of the solution.

Experiments also show that the drop in freezing does not depend on the type of solute, but depends only on the concentration of the solution.

The decrease in the molasses freezing point is the value of the freezing drop if the concentration of the solution is one mol.

Electrolyte ΔTf = Kf x m x i

Non Electrolyte ΔTf = Kf x m

D. Tools And Materials

Tool:

1. Balance Sheet

2. Test tube

3. Spoon

4. Mixer Stem

5. Glasses of chemicals

6. Thermometer

7. The reaction tube shelf

Material:

1. Distilled water

2. Ice cubes

3. Urea 1 m & 2 m

4. NaCl 1 m & 2 m

E. Introduction to Experiments

Freezing point, a pure liquid has a certain freezing point value. If the pure liquid has been mixed with other substances, the freezing point may change and the change is dependent on the mixing agent. At each temperature, the vapor pressure of the solution is lower than the vapor pressure of the solvent thereby causing the freezing point of the solution to be lower than that of the solvent freezing point. The increase in the boiling point and the decrease in freezing point is one of the colligative properties of the solution.

F. Safety

1. Materials used, not to be swallowed.

2. Ingredients of asthma / bases used, do not get exposed to skin, if exposed to the skin immediately rinse with running water.

3. In each observation made, keep your eye distance to the observed material, be careful not to expose the effects of the substance / reaction that occurs. If exposed immediately rinse with water.

4. Clean (wash) the equipment every time after the experiment is used. The reaction tube is cleaned with a reaction tube brush.

G. Experimental Procedure

The unit of concentration of molality (m) represents 1 mol of solute in 1000 grams of solvent.

1. Prepare a 250 ml glass of water and fill it with ice cubes that have been crushed until the volume reaches approximately 3/4 tall glass of chemistry. Sprinkle the ice cubes with salt.

2. Insert 5 ml of water into the test tube, then insert the test tube into a glass containing the ice. Adjust the position of the tube soaked in ice in the beaker.

3. Stir the contents of the test tube by slowly stirring the stir bar (not stirring in a circle) until the liquid in the tube completely frozen.

4. Remove the test tube from inside the beaker and let the ice in the tube melt slightly.

5. Remove the stir bar and insert the thermometer. Stir back the water by throwing the thermometer (be careful not to stop the thermometer and then break) and then read the temperature (the temperature will decrease and then increase again, take the lowest temperature).

6. Repeat steps 1-5 using urea, 1 m and 2 m solutions, and a solution of NaCl, 1 m and 2 m.

I. Discussion

A solution will freeze at a lower temperature than the freezing point of water. To learn this further needs to be understood about freezing. What is meant by freezing is the temperature at which the liquid phase and the solid phase are together (in equilibrium).

The normal freezing point of a liquid is a freezing point at a pressure of 760 mmHg or 1 atm. For example pure water freezes at a fixed temperature, ie 0 ˚C at 1 atm pressure. Decrease in freezing point is proportional to the amount of solute concentration is greater then the bigger the frozen point is also greater. Thus, in the presence of solutes in water, the freezing point of water becomes less than 0˚C at 1 atm pressure.

If we pay attention to the making of the swivel ice, to obtain a lower temperature and 0 ˚C then the rotating ice dough is placed in a vessel submerged in ice cubes and water that has been given the salt of the kitchen, while rotated and stirred then the ice batter in the vessel will freeze, Where the freezing point of the rotating ice dough is a few degrees below the freezing point of pure water. This happens because there is a process of heat transfer from the ice batter into a mixture of ice cubes, water and salt. For more details can be seen and the following picture:

Images change the pure water ice cubes and the process of freezing ice

Information:

○ = pure solvent particles

● = solute particles

If the pure water in a container is immersed in ice cubes and the pure water salt will freeze at a certain temperature (normally 0 C measured at 1 atm pressure). While at the same temperature, the ice dough has not been perfectly frozen or has not even frozen. The presence of substances or solutes added in the rotary ice dough prevents the purge of the purified solvent molecules to freeze normally, so that the freezing point of the solution decreases (a decrease in freezing), resulting in a lower temperature to freeze it.

Thus, it is clear that the solution will freeze at a lower temperature than the freezing point of water. The difference between the freezing point of the pure solvent and the freezing point of the solution is called the decrease of the freezing point of the solution denoted by ΔTf.

          ΔTf = Tºf - Tf

Information:

ΔTf = decrease of freezing point

Tºf = freezing point of solution

Tf = freezing point of solvent

The freezing point does not depend on the type of solute, but depends only on the concentration or the amount of solute particles in the solution. So, the greater the concentration of the solution the greater the freezing point. Mathematically writable:

Information:

ΔTf = decrease of freezing point

Kf = the molal freezing drop point

M = concentration of solution

G = mass dissolved in grams

P = solvent mass in grams

Mr. = the relative molecular mass of the solute

Where, Kf is the same as the molecular freezing point constant, ie the value of the freezing point of the solution as much as 1 mole of solute in 1000 grams of solvent (Kf). The price of Kf depends on the properties of the liquid used as the solvent, so the price of Kf for each solvent varies.

Application in Everyday Life

.

A. Creating a Cooling Blend

The coolant is an aqueous solution that has a freezing point well below 0oC. Coolant liquids are used in ice factories, also used to make ice turns. The coolant is made by dissolving different types of salt into the water. In the manufacture of ice, the cooling liquid is made by mixing the kitchen salt with ice cubes in a wood-lined vessel. At the mixing, the ice cubes will melt while the mixed temperature falls. Meanwhile, the mixture of swivel ice maker was put into another vessel made of stainless steel. The vessel is then fed into the coolant, while continuously stirring so the mixture freezes.

B. Anti-freeze on Car Radiators

In cold climates, the water of the radiator is usually added ethylene glycol. In areas with cold climates, the radiator water is easily frozen. If this situation is allowed, then the vehicle radiator will be quickly damaged. With the addition of ethylene glycol into the water the radiator is expected to freeze the water in the radiator decreases, in other words the water does not easily freeze.

C. Antibeku in Animal Body

Animals living in cold climates, such as kutup bears, utilize the principle of the colligative nature of frost reduction solutions to survive. The blood of sea fish contains antifreeze substances capable of lowering the freezing point of water up to 0.8oC. Thus, the latter can survive in winter where the temperature reaches 1.9oC because the antifreeze it contains can prevent the formation of ice crystals in tissues and cells. Other animals whose bodies contain antifreeze substances among insects, amphibians, and nematodes. Insect body contains glycerol and metal sulphoxide, amphibians containing glucose and blood glycerol while nematode contains glycerol and trilose.

D. Anti-freeze to Liquid Snow

In an area that has winter, every snowfall occurs, the streets are filled with snow ice. This of course makes the vehicle difficult to drive. To overcome this, the snowy streets are sprinkled with a mixture of salt NaCl and CaCl2. The sowing of salt is sown, the more snow will melt.

E. Determining Relative Molecular Mass (Mr)

The measurement of the colligative properties of the solution can be used to determine the relative molecular mass of the solute. It can be used because the colligative nature depends on the concentration of the solute. Knowing the dissolved mass can be determined.

J. Conclusions

The conclusions of the experiments that have been done are as follows:

1. What is the function of adding salt to ice cubes?

Answer: The function of adding salt to ice cubes is as a substance that lowers the freezing point of ice cubes so that ice cubes will not freeze at 0 ° C.

2. What is the decrease in freezing point for each solution?

In the urea solution the molality of 1 m of the freezing point - 3oC and molalitas 2 m of freezing point - 6 oC. While in NaCl solution molalitas 1 m freezing point - 5 oC and molalitas 2 m freezing point -9 oC.

3. What is the relationship between the molality of the solution and the decrease in its freezing point?

Answer: The relationship between the molality of the solution and the decrease in the freezing point is the greater the molality the greater the freezing point. This relationship can be formulated as follows:

ΔTf = Tºf - Tf

Information:

ΔTf = decrease of freezing point

Tºf = freezing point of solution

Tf = freezing point of solvent

4. How does the freezing point drop for urea and NaCl solutions in the same molality? Explain?

Answer:

At the same molality, the decrease of freezing point of NaCl (electrolyte) solution is higher than that of urea (non-electrolyte) solution. Because the electrolyte substances decompose into ions so that the number of particles more than non-electrolyte substances.

5. The greater the molality of the solution, the higher the decrease in the freezing point of the solution.

6. Decrease of the freezing point of the solution (Tf) is directly proportional to the molality of the solution.

7. The freezing point of pure solvent is higher than the freezing point of the solution.

8. The freezing point of the electrolyte solution is lower than the non-electrolyte solution in the same kemolalan.

9. The smaller the concentration of the solution, the greater the antarion distance and the more free ions.

10. For the same concentration, the electrolyte solution contains more number of particles than the non-electrolyte solution.

11. Electrolyte solution has a greater colligative properties than non-electrolyte colligative properties.

12. The higher the kemolalan the lower the freezing point.

13. The higher the kemolalan the greater the decrease in the freezing point.

K. Follow Up

1. Look for examples of events in everyday life that indicate a decrease in freezing?

Answer: Examples of events in everyday life that indicate the occurrence of a decrease in freezing is as follows:

The presence of solutes in the solution will cause the freezing point of the solution to be smaller than the freezing point of the solvent. For example salt can melt the snow. Another example is that the snow on the road in the winter country is easy to clean by adding salt, thereby lowering the freezing point of the solution, so the freezing point of the solution (salt + snow) will be lower than the freezing point of the snow melting ice on the road by sprinkling salt. As well as on the ice cream mixture does not freeze due to the decrease in freezing point. Additionally Prevention of water freezing of car radiators during winter in Europe also uses applications of the colligative nature. Even some animals that have poles or sea with cold temperatures also use a chemical compound (salt) in his blood so as not to freeze to death.

Daftar Pustaka

http://chemistranger.blogspot.com/2012/07/sifat-koligatif-larutan.html

http://fathur30rahman.blogspot.com/2014/04/laporan-praktikum-kimia-penurunan

titik.html

http://riski-seftiani.blogspot.com/2012/11/laporan-pratikum-kimia.html

http://www.slideshare.net/Andirahim/kimia-kelas-12-ariharnanto

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titik-beku.html

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