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Anew Bosbo Background Freezing point depression describes the process where the temperature at which a liquid freezes is lowered by adding another compound. It depends only on the number of dissolved particles in solution. This is known as a colligative property. For example, water freezes at 0 °C, but when a solute such as salt or sugar is added to a solvent (water), the freezing point decreases. In order to see the freezing point depression of saltwater and how it changes with varying amounts of solute concentration, you will use 5 cups with water and varying amounts of salt and measure each individual temperature. Then, using the volume of the water and the volume of the solute, you will find the concentration of the solution expressed in molality. In the second part of the lab, you will use two freezer bags to observe how readily water freezes when surrounded by saltwater. PROCEDURE : You will be asked to complete a Table at various steps. The Table is located at the end of Part 1. You will need to submit answers to all questions and the table for full credit. Write the response to the question directly below the question. Partl 1. Setup 5small cupsin aline in front of you. 2. Label the cups - “0 mL of Salt”, “10 mL of Salt”, “20 mL of Salt”, “30 mL of Salt”, and “Sugar”. 3. Fill the measuring cup to about 100 mL of crushed ice. Slowly pour water into the cup until the ice/water mixture reaches 100 mL. (If your measuring cup does not measure in mL, 100 mL is a little less than half a cup.) Fill the first 4 salt cups with 100 mL of ice/water. 4. Measure out respective amounts of salt outlined in step 2, using tablespoons and teaspoons. Note: 1 teaspoon = 5 mL and 1 tablespoon=15 mL. The sugar will be added to the last cup in step 8. 5. Stir the amount of salt into each cup until the salt dissolves. Note: If the saltwater is not continually stirred, the salt will pile up at the bottom. Stir slowly to ensure salt dissolves. Also, for 30 mL of solute, add the solute in portions. (Example: 10 mL first and then 20 mL later). Question 1: Why does the 10 mL of salt dissolve more readily than the 30 mL of salt? How does the temperature of the solution affect the solubility of the solution? (2 points) T smalled amount o Sat AisseWes Zu?d'st( beane ghere 5 LESS. So\ubi\\'kj n3es wivh rempel arure o\ afbteeks Soluton. Q2. What other factors can you think of that might affect the solubility of the solution? (1 point) The subace acea gud Hhe amant of Seirng ok & done 6. After you have stopped stirring, wait for the temperature to reach equilibrium. This temperature is the “freezing point” of the solution. Using your thermometer, measure the temperature of each solution and record the temperatures in Column B of Table 1. Q3. How did the freezing point change by increasing the amount of salt in the water? (1 point) Treedy oot g lawer MY inceged adition of Saw. 2 CHEM-126

7. Using a strainer, strain the ice out of each cup. Measure the volume of the remaining liquid (salt water) using the graduated measuring cup. Record the results in Column C of Table 1. 8. Inthe final cup, add 30 mL of sugar solute into 100 mL of cold water. Record the freezing temperature in Table 1. Q4. How does the freezing temperature obtained by sugar water compare to the freezing temperature obtained when 30 mL of salt were added to the same amount of water? (1 point) The (reeaing point was &iehBR it Suger Colive amd LoweR with %\\- QO\U‘\(. Table 1 (10 points) Column A Column B Column C Column D Column E Column F Column G Temperature Strained Mass of Salt Kilograms of . Solute () Water (mL) ©® Moles of Salt Molality 0 mL salt O (/ woar | g | Wl | my o [SRY, |1t 20mLsalt | ~4° q,z:.m\; oHUL O\ 3-'-\1& e 5, 5oy sa - N 7 ML 15\ ;\ 5 ) somLsalt | ~\) 7 %5 ©.5% ,%04%0555\7) K mL bl Svear -°C Concept Questions Find the molal concentration (or molality) of each solution using the equation below. First, find the moles of solute and mass of solvent. Follow the steps below to find these values. Moles of solute (mol) Mass of solvent (kg) Molality (mol/kg) = 3 CHEM-126

Q6. Plot a molality vs, freezing temperature 8raph. Describe the relationship, (2 point) AS MOTY inreases HAeN we 4e€ dlecrense " C ( :c}v\fi RW\P Freezing Temperature Saw hawng onic by nd R I S T P (_:m\p\{):(f\‘) A\SSociade i ne So\ution. Q8. What freezing temperature would You predict if 40 mL of salt was placed in the water? (1 point) Part 2: Freeze Water with Water 1. Add crushed ice into the gallon freezer bag until the bag is % ful. Take the temperature. Recorg below: U CHEM-126

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