2.1 Equipment
Apparatus
• 1 Data Logger
• 1 Temperature Probe
• 1 Gram balance
• 1 250ml beaker
• 5 Test tubes
• 1 Stirrer
• 1 400ml Beaker
Materials
• Table salt (Sodium chloride/ NaCl)
• Water (H2O)
• Ice
2.2 Diagram
1. Fill a 400ml beaker 3/4 full of ice. Put salt into the beaker of ice and mix the the ice and the salt
along with a stirring rod. This is the ice bath to freeze the various solutions. This mixture has to be at least -10 ℃. Remove any excess water that has melted to prolong the ice bath.
2. Label the 5 test tubes to test tube 1, 2, 3, 4 and 5. Different test tubes will contain different solutions:
• Test liquid #1 = 0g NaCl in 100 ml water
• Test liquid #2 = 1.1 g NaCl in 100 ml water
• Test liquid #3 = 2.1 g NaCl in 100 ml water
• Test liquid #4 = 3.1 g NaCl in 100 ml water
The ones with salt added in the test tube would be weighed by a gram scale. Place each test tube one at a time in the ice bath.
3. Allow some time for the solution in the test tube to cool down. After about 5 minutes, insert the temperature probe that is connected to the data logger into the test tube. Wait until the temperature reaches a fixed temperature. The temperature is the freezing point of the solution inside the beaker.
Do this for the other test tubes with other solutions for at least 3 times to ensure reliable results.
2.3 Procedures
Creating the ice bath
1. Fill the Beaker 3/4 full with ice.
2. Cover the ice with 1/4 to 1/2 inches of table salt.
3. Stir this ice-salt mixture with a stirring rod.
4. Use the thermometer to check the temperature of the ice-salt mixture. It should be at least −10° C.
Experiment on the Freezing Point of different solutions
1. Prepare the first test liquid in the beaker labeled #1.
- Put beaker "#1" on the gram scale.
- Zero the gram scale.
- Put table salt (NaCl) into the beaker. For test liquid 1, there will be 0 g NaCl in 100 ml water. For test liquid 2, put 15 g NaCl in 100 ml water. For test liquid 3, put 20g NaCl in 100 ml water. For test liquid 4, put 25g NaCl in 100 ml water. For test liquid 5, put 30g NaCl in 100 ml water
- Take the beaker off the scale and place the beaker on a stable surface.
- Measure 100 ml of water in a graduated cylinder, and pour it into the beaker with the salt. Stir with a spoon or stirring rod until all of the crystals are dissolved.
- Rinse the spoon or stirring rod with water to clean off the salt so as to prevent contamination of the next mixture.
2. Fill test tube #1 half-way full with test liquid #1. Place the test tube in the styrofoam cup with the ice and salt.
- The liquid in the test tube should be below the level of the ice and salt in the cup to ensure that the solution is fully chilled.
- Any ice or salt from the cup is not allowed to get into the test tube.
3. Stir the test liquid in the test tube gently with a stirring rod while keeping track of the temperature with the thermometer.
4. When the first ice crystals appear on the inside wall of the test tube, the temperature will be recorded into the log book. The temperature is the freezing point of the test liquid.
5. Empty the test tube, and then refill the same test tube with freshly mixed test liquid #1. Repeat steps 1 through 4 with a new sample. Then empty and refill the test tube again, repeating steps 1 through 4 for a third time.
- To make more of the test liquid, repeat step 3.
6. Repeat steps 1-5 for each of the remaining test liquids, making sure to use a different beaker and test tube for each of the test liquids. Ensure that all beakers are labelled so as to avoid confusion.
- Calculate the freezing point depression, ΔT, for all three replicates of each of the NaCl solutions. Record these values for ΔT in the group’s lab notebook.
7. First, average the freezing point temperatures you observed for plain water test. This averaged temperature will be the solvent freezing temperature.
8. Average the freezing point depression, ΔT, for each of the NaCl solutions. Record these averages in the group’s logbook for comparison.
2.4 Risk Assessment and Management
1. Students must wear gloves and goggles to protect themselves.
2. Students must wash their hands after the experiment so as to prevent contamination by the liquid
3. Students must make sure they do not touch the mixture for extended period of time to prevent frostbite
4. We must not spill the mixture onto the floor as people might slip and fall
5. If come into contact with solution, wash hands with soap and water to prevent any injuries
5. We must take precaution while using fragile materials such as glass to prevent them from falling and breaking.
7. When the glass breaks, do not pick up the broken pieces with bare hands. Alert the teacher or lab manager first. Clean up the broken pieces with a broom and dispose them into the allocated waste disposal bin.
2.5 Data Analysis
First, we record the various raw data that we have collected from the experiments and then find the average of the experiment. Then, we create a graph to sort out our results. Then, we compare the average of the data collected as well as the graph to see the decrease or increase in temperature of the freezing point. From this, we will be able to obtain our answers.
Mass of Salt in the Concentration of Water
(g)
|
Freezing Point of Solution (°C)
|
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