FREEZING POINT DEPRESSION- MAKING ICE CREAM IN A BAG
- ¼ cup sugar
- ½ cup milk
- ½ cup hey whipping cream
- ¼ teaspoon of vanilla extract or vanilla flavoring
- 1-quart size zipper top baggie
- 1-gallon size zipper top baggie
- 2 cups ice
- ½ to ¾ cup table or rock salt
- Measuring cups and spoons
- Cups and spoons for eating your product
- Add ¼ cup sugar, ½ cup milk, ½ cup whipping cream, and ¼ vanilla extract to the quart size zipper top bag. Seal the bag securely.
- Put two cups ice in the gallon size bag.
- Use the thermometer to measure the initial temperature of the ice in the plastic bag. Record this temperature.
- Add ½ to ¾ cup salt to the bag of ice.
- Place the sealed quart size bag inside the gallon size bag. Seal the bag securely.
- Hold the top of the gallon size bag and gently rock the bag side to side. Where gloves if you have them; if not, keep your hands away from the area of the bag that contains the ice. It is cold enough to damage your skin.
- Continue to rock the bag for 10-15 minutes or until the contents of the quart size bag solidifies into ice cream.
- Open the gallon size bag and use the thermometer to take the temperature of the ice/salt mixture. Record this temperature.
- Remove the quart size bag, open it, serve the ice cream into cups and enjoy your product!
PLEASE SHOW ALL WORK FOR CREDIT AND BOX YOUR ANSWERS
- What is a colligative property? Use complete sentences.
- Explain why freezing point of a solution depresses and boiling point elevates compared to the pure solvent. Use diagrams and complete sentences.
- If the density of milk is 1.035 g/cm3 and the freezing point is -0.250 oC, calculate the Kf for milk. Assume the whipping cream is milk and therefore your pure solvent is milk. The formula for sugar is C12H22O11. Use one dry 1 oz = 28.35 g. Show all your work!
- How would using sodium carbonate effect the temperature depression? Explain your answer.
POST LABS QUESTIONS
- A solution is prepared by dissolving 4.9 g of sucrose (C12H22O11) in 175 g of water. Calculate the freezing point of this solution.
- The freezing point of t-butanol is 25.50 oC and has a Kf of 0f 9.1 oC/m. Usually t-butanol absorbs water on exposure to air. If the freezing point of a 10.0 g sample of t-butanol is 24.59 oC, how many grams of water present in the sample?
- Is the freezing point of 0.01 m KF(aq) higher or lower than that of 0.01M glucose(aq)?
- A .350 g sample of a large biomolecule was dissolved in 15.0 grams of chloroform, and the freezing point depression was determined to be 0.240 oC. Calculate the molar mass of the biomolecule (Kf for chloroform is 4.70 oC/m).
- In the winter of 1994, record low temperatures were registered throughout the United States. For example, in Champaign, Illinois, a record low of –29 oF was recorded. At this temperature can the salting of icy roads with calcium chloride be effective in melting the ice? Assume the solubility of calcium chloride in cold water is 74.5 g per 100.0 grams of water.
- mA forensic chemist is given a white solid that is suspected of being pure cocaine (C7H21NO4, molar mass = 303.35 g/mol). She dissolved 1.22 0.01g in 15.60 0.01g benzene. The freezing point is lowered by 1.32 0.04 oC.
- What is the molar mass of the substance?
- Assuming that the percent uncertainty in the calculated molar mass is the percent uncertainty in the temperature change, calculate the uncertainty of the molar mass.
- Could the chemist unequivocally state that the substance is cocaine? For example, is eth uncertainty small enough to distinguish cocaine from codeine (C18H21NO3, molar mass =299.36 g/mol)?
- If the absolute uncertainties in the measurements of temperature and mass remain unchanged, how could the chemist improve the precision of her results?
11. What difficulty did you encounter in this lab and how would you modify the lab top make it better?