Mls121l04_measurements.docx

MLS 121L (Inorganic and Organic Chemistry Laboratory): Activity 04 MEASUREMENTS IN CHEMISTRY I.    

Aims To calibrate a volumetric glassware To use a calibrated volumetric pipet in determining the density of a solution To accurately measure the boiling point of a solution To report all measured quantities observing proper number of significant figures

II.

Materials and Apparatus/Equipment

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250-mL Erlenmeyer flask Thermometer 10-mL volumetric pipet 50-mL beaker Microboiler tube Iron stand with ring Iron clamp Analytical balance

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Distilled water M NaOH solution Glycerol III.

Activities

Calibrating a volumetric pipet with water 1. Clean a 250 mL Erlenmeyer flask by rinsing with distilled water three times. After rinsing, fill the flask with distilled water. This shall serve as your water reserve. 2. Place a thermometer into the flask and set aside until the temperature of the water stabilizes. Record the temperature reading and look up the density of water at this temperature. Express the literature value in g/mL if it is not already in those units. Be sure to record a proper source citation. 3. Obtain a 10-mL volumetric pipet. Rinse it thoroughly with distilled water three times. Record the information on the stem of the volumetric pipet you are using. 4. Clean and dry a 50-mL beaker, taking care not to handle it by bare hands after it has dried. Weigh the beaker and record its mass. 5. Using the volumetric pipet, add 10.00 mL of distilled water from your water reserve to the 50-mL beaker. Obtain the mass of the beaker with water in it then discard the water after. 6. Repeat until you have a total of four mass and volume measurements. 7. For each set of mass and volume measurements, calculate the volume of water delivered in each trial using the literature value of the density of water at the recorded temperature to convert mass to volume.

8. Calculate the mean volume of water delivered. Calculate the standard deviation of the volume of water delivered. 9. Summarize these results by writing the mean volume ± the standard deviation. This is your best determination of the actual volume being delivered by your pipet. Determining the density of a solution 1. Obtain 60 mL of 0.1 M NaOH solution into a clean and dry beaker previously rinsed thrice with the solution. This will serve as your solution reserve. 2. Pour about 10 mL of the same solution from the stock reagent bottle into another small beaker then pipet some of this solution to rinse the pipet three times. Dispose of the waste rinse. 3. Clean and dry a 50-mL beaker, taking care not to handle it by bare hands after it has dried. Weigh the beaker and record its mass. 4. Using the volumetric pipet, add 10.00 mL of 0.1 M NaOH solution from solution reserve to the 50mL beaker. Obtain the mass of the beaker solution in it then discard the solution after. 5. Repeat until you have a total of four mass and volume measurements. 6. For each set of mass and volume measurements, calculate the density of solution. Calculate the mean density of the solution from these measurements. Calculate the standard deviation of the solution density from these measurements. 7. Summarize these results by writing the mean density ± the standard deviation. This is your best determination of the density of the solution. Look up how your measured density compares to literature values. Determining the boiling point of a solution 1. Place 3 mL of 0.1 M NaOH solution into a test tube. Insert a microboiler tube into the assembly with its shorter end first. 2. Attach the microboiler tube by rubber band to a thermometer with the liquid alongside the mercury/alcohol bulb. 3. Immerse the thermometer-microboiler tube assembly into a glycerol bath ensuring that the rubber band is above the glycerol level. 4. Heat gradually until a rapid and continuous stream of air and vapor comes out from the microboiler. Remove heat source when your reach rapid bubbling. 5. Observe carefully and note the temperature at which the bubbling ceases and the liquid just starts to rise up the microboiler tube. Record this as your first boiling point reading. 6. Repeat to complete three trials. 7. Calculate the mean boiling point measured. Calculate the standard deviation of the three measurements done. 8. Summarize these results by writing the mean boiling point ± the standard deviation. This is your best determination of the boiling point of the solution. Look up how your measured boiling point compares to literature values. Using data from these activities, discuss the relevance of accuracy and precision in doing measurements in the chemistry laboratory. Account for deviations by identifying random and systematic errors.