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Passage I Freezing point depression occurs when a substance solute is added to a solvent decreasing the solvent s freezing point The process can be monitored over a short range depending on the solute by using a hydrometer which floats in the solution at varying depths as an indication of the mixed solution s specific gravity Freezing point is the temperature at which the solution becomes a solid at normal atmospheric pressure Three experiments were performed using distilled water mixed with precise amounts of ethylene glycol CHO propylene glycol C H O or methanol CH O in concentrations varying from 10 90 by weight All solutions were aqueous with a starting temperature of 25 C A hydrometer was used to indicate the relative change in specific gravity as the solute percentage was increased Table 1 shows the density for each of the three solutes Solute ethylene glycol propylene glycol methanol Entrance Ticket Table 1 6 4 1 Set One Density 1 110 00 kg m 1 040 00 kg m 791 30 kg m Experiment 1 Distilled water was mixed with precise concentrations of ethylene glycol in various concentrations by weight For each concentration a hydrometer was used to measure specific gravity at 25 C and the freezing point was determined using a precision thermometer Figure 1 shows results through 50 concentration freezing point C freezing point C 25 30 35 40 15 20 25 30 35 40 0 5 10 15 20 0 5 0 10 Learning Targets Trends in Data Puzzle Pieces 0 Experiment 2 Experiment 1 was repeated except propylene glycol was used instead of ethylene glycol Figure 2 shows results through 50 concentration Key freezing point specific gravity 1 10 20 30 40 50 ethylene glycol concentration Figure 1 Key freezing point specific gravity 40 10 20 30 50 propylene glycol concentration ACT Practice Figure 2 1 09 1 08 1 07 1 06 1 05 Sum It Up 1 04 1 03 1 02 1 01 1 06 1 05 1 04 1 03 1 02 specific gravity 1 01 1 00 specific gravity Experiment 3 Experiment I was repeated except methanol was used instead of ethylene glycol and specific gravity was not recorded because of methanol s low evaporation point Figure 3 shows results for all concentrations of the three solutes freezing point C 0 10 20 30 40 50 60 70 80 90 100 0 Key ethylene glycol propylene glycol methanol 20 F G H J 40 60 80 solute concentration Figure 3 1 In Experiment 1 if 60 ethylene glycol had been added to the sample the freezing point would most likely have been A greater than 15 C B between 15 C and 25 C C between 25 C and 35 C D less than 35 C 100 2 Consider two of the solutes temporarily named Solute A and Solute B At increasing concentrations both solutes initially provided similar levels of freeze protection At 70 concentration however Solute B began to lose effectiveness while Solute A continued to provide an increasing level of freeze protection as concentration increased What are the actual names for Solutes A and B Solute A ethylene glycol propylene glycol methanol propylene glycol Solute B propylene glycol methanol ethylene glycol ethylene glycol 3 Suppose another concentration of propylene glycol had been tested in the same way described in Experiment 2 The specific gravity for a 60 propylene glycol solution would most likely have been Entrance Ticket Learning Targets A greater than 1 04 B between 1 02 and 1 04 C between 1 01 and 1 02 D less than 1 01 4 Based on Table 1 the mass of 0 5 m of propylene glycol would be closest to which of the following values F 395 65 kg G 520 00 kg H 555 00 kg J 791 30 kg 5 Based on the results of the three experiments which of the following combinations of solute solute weight and solution weight will provide the lowest possible freezing point Trends in Data A B C D Solute Weight Solution Weight Solute 80 lbs 200 lbs 70 lbs 280 lbs 90 lbs 150 lbs 180 lbs 90 lbs END OF SET STOP DO NOT GO ON TO THE NEXT F UNTIL TOLD TO D Puzzle Pieces methanol ethylene glycol ethylene glycol propylene glyco ACT Practice Sum It Up

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