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Experiment 19
Objective: The objective is to become familiar with colligative properties and to use them to determine the molar mass of a substance.
Materials and chemicals:
800mL beaker balance weighing paper Thermometer
400mL beaker wire stirrer ring stand unknown solid
15x150mm test tube clamp watch acetone
Ice cyclohexane sodium chloride
Lab Safety:
Wear protective googles, apron, and gloves.
Procedures:
Prepare ice/salt/water bath
Place 50g of solid NaCl in a 400mL beaker and add just enough water to dissolve the salt.
Fill an 800mL beaker 2/3 full of ice, and then pour salt water mixture into the beaker, stir.
In the hood, into two nested test tubes, add 10 mL of cyclohexane from a buret.
Record initial and final buret readings. Then measure the volume of the cyclohexane to the nearest .05mL, calculate the mass and place a thermometer in the cyclohexane with a wire stirrer around the thermometer. Clamp test tube on ring stand and lower into the salt water bath.
Gently stir until crystals form. Then raise test tube out of the bath and record temperature to the nearest .2 C every 30 seconds until the temperature reaches about 12 C to 15 C.
Repeat process and graph the temperature and time and then determine freezing point of cyclohexane.
B-Determination of the Molar Mass of an Unknown.
Using weighing paper, weigh about .3 to .4 of the unknown to the nearest .001g.
Add unknown to the cyclohexane in the test tube and stir gently with wire stirrer until all of the unknown has dissolved.
Place test tube into salt water ice bath and stir until it becomes slushy.
Raise the test tube out of the bath and record temperature to the nearest .2 C until temperature reaches 10 to 15C. Then repeat process.
C-Clean Up
In the hood, pour cyclohexane solution and excess unknown into the appropriate waste container. Rinse test tubes with a few mL of acetone and add the acetone rinse to the waste container. Then place test tube in locker to air
Objective: The objective is to become familiar with colligative properties and to use them to determine the molar mass of a substance.
Materials and chemicals:
800mL beaker balance weighing paper Thermometer
400mL beaker wire stirrer ring stand unknown solid
15x150mm test tube clamp watch acetone
Ice cyclohexane sodium chloride
Lab Safety:
Wear protective googles, apron, and gloves.
Procedures:
Prepare ice/salt/water bath
Place 50g of solid NaCl in a 400mL beaker and add just enough water to dissolve the salt.
Fill an 800mL beaker 2/3 full of ice, and then pour salt water mixture into the beaker, stir.
In the hood, into two nested test tubes, add 10 mL of cyclohexane from a buret.
Record initial and final buret readings. Then measure the volume of the cyclohexane to the nearest .05mL, calculate the mass and place a thermometer in the cyclohexane with a wire stirrer around the thermometer. Clamp test tube on ring stand and lower into the salt water bath.
Gently stir until crystals form. Then raise test tube out of the bath and record temperature to the nearest .2 C every 30 seconds until the temperature reaches about 12 C to 15 C.
Repeat process and graph the temperature and time and then determine freezing point of cyclohexane.
B-Determination of the Molar Mass of an Unknown.
Using weighing paper, weigh about .3 to .4 of the unknown to the nearest .001g.
Add unknown to the cyclohexane in the test tube and stir gently with wire stirrer until all of the unknown has dissolved.
Place test tube into salt water ice bath and stir until it becomes slushy.
Raise the test tube out of the bath and record temperature to the nearest .2 C until temperature reaches 10 to 15C. Then repeat process.
C-Clean Up
In the hood, pour cyclohexane solution and excess unknown into the appropriate waste container. Rinse test tubes with a few mL of acetone and add the acetone rinse to the waste container. Then place test tube in locker to air