Density Laboratory: Understanding, Calculating, and Identifying Substances through Precise Measurements and Analysis

In the density laboratory, we had four primary goals to accomplish:

1. Understand intensive and extensive properties.
2. Calculate the density of regularly-shaped objects.
3. Calculate the density of irregularly-shaped objects.
4. Calculate the density of distilled or deionized water.

To determine the density of an object, whether regular or irregular in shape, knowing its mass and volume is crucial (Density = Mass of object / Volume of object). Mass and volume are considered extensive properties as they depend on the quantity of an object. In contrast, density is an intensive property because it does not rely on the quantity but rather the substance's nature.

Density is typically expressed in units such as g/ml or g/cm^3 at 20°C. Recording the temperature is essential as it affects volume, influencing the density calculation. The density of a substance remains constant at constant temperatures, enabling identification of different substances based on their density.

During this experiment, we measured both the volume and mass of regularly-shaped objects, irregularly-shaped objects, and ionized and deionized water to calculate their respective densities.

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The following table provides density values for various substances used in this experiment.

The primary objectives of this laboratory experiment are to understand intensive and extensive properties, determine the density of regularly-shaped and irregularly-shaped objects, and calculate the density of distilled or deionized water.

A. Determining the Density of Regularly-Shaped Objects:

1. Selecting the Object: Obtain one of the solid blocks provided in the lab and record its code number on the data sheet.
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2. Measuring Dimensions: Utilize a metric ruler to measure the length, height, and width of the block. Record these measurements. Calculate the volume of the cube using the formula: Volume=Length×Width×HeightVolume=Length×Width×Height.
3. Measuring Mass: Determine the mass of the block using a top-loading balance to the nearest 0.01g.
4. Calculating Density: Use the formula Density=MassVolumeDensity=VolumeMass​ to calculate the density of the block. Record the result on the data sheet.
5. Repeat and Average: Optionally, repeat the experiment to verify results. Calculate the average density.
6. Comparison with Density Table: Compare the calculated density with values from the density table to identify the substance of the cube.

B. Determining the Density of Irregularly-Shaped Objects:

1. Selecting the Object: Obtain an unknown metal sample from the Styrofoam cups in the lab and record its number on the data sheet.
2. Measuring Mass: Use the top-loading balance to approximate the mass of approximately 5 grams of the unknown metal. Record the value.
3. Water Displacement Method: Utilize a 10-ml graduated cylinder to measure the initial volume of water. Place the metal sample in the graduated cylinder and tap to remove air bubbles. Measure the final volume and determine the volume of the metal by finding the difference.
4. Calculating Density: Determine the density of the metal sample using the formula Density=MassVolumeDensity=VolumeMass​. Record the result on the data sheet.
5. Comparison with Density Table: Compare the calculated density with values from the density table to determine the identity of the substance.

C. Determining the Density of Water:

1. Preparing the Beaker: Obtain and dry a 50 ml or 100 ml beaker. Weigh the beaker and record its mass to the nearest 0.01 g.
2. Measuring Water: Transfer 30 ml of distilled or deionized water into a clean beaker (labeled beaker 2). Measure the water temperature and record it.
3. Transferring Water: Transfer 10.00 ml of water to the pre-weighed beaker labeled beaker 1 using a 10-ml volumetric pipet.
4. Measuring Mass: Weigh beaker 1 with the 10 ml of water and record its mass.
5. Calculating Mass of Water: Calculate the mass of the water by subtracting the mass of the empty beaker from the mass of the beaker containing water.
6. Calculating Density of Water: Use the formula Density=MassVolumeDensity=VolumeMass​ to calculate the density of water. Record the result on the data sheet.
7. Comparison with Standard Density: Compare the measured water density with the standard value of 1.0 g/ml, as per the lab book.

Summarize the findings and discuss any discrepancies. Relate the calculated densities to the identity of the substances. Reflect on the accuracy of the measurements and the importance of considering temperature in density calculations.

Density Determination:

1. Regularly-Shaped Object:
   • Density: 0.65 g/cm³
   • Identity: Oak
2. Irregularly-Shaped Object:
   • Density: 7.1 g/ml
   • Identity: Steel
3. Distilled Water:
   • Density: 1.003 g/ml
   • Agreement with Literature: True

The calculated densities align with the expected values based on known substances, validating the accuracy of the experimental procedures. The identified substances (Oak and Steel) are consistent with the density constants at 20°C. However, potential errors, such as the room temperature being 21°C instead of 20°C, were acknowledged. The sensitivity of density to temperature underscores the importance of precise measurements.

Possible Errors:

1. Pipet Usage:
   • Air Bubbles: Lowered density due to underestimated volume and mass.
   • Dirty Pipet: Elevated density due to overestimated volume.
2. Experimental Pace:
   • Rushed Experiment: Inexact measurements leading to potential density discrepancies.

Impact of Invalid Measurements:

• Inaccurate measurements of volume and mass can significantly impact density calculations, making it challenging to identify unknown substances.

Post Lab Questions:

1. Effects on Density Determination:
   • a. Air Bubbles:
     • Density: Lower
     • Explanation: Bubbles result in underestimated volume and mass, leading to a lower density.
   • b. Dirty Pipet:
     • Density: Higher
     • Explanation: Higher volume due to water droplets results in an overestimated mass, leading to higher density.
   • c. Insufficient Waiting Time:
     • Density: Lower
     • Explanation: Incomplete liquid emptying leads to lower volume and mass, resulting in lower density.
2. Same Mass, Different Density:
   • No, two objects with the same mass but different densities would not have the same volume. Density is the ratio of mass to volume (D = M/V). If two objects have the same mass but different densities, their volumes must differ.
3. Density Calculation for a Regularly Shaped Object:
   • Mass (M): 56.88g
   • Dimensions:
     • Length (L): 3.65cm
     • Width (W): 8.97cm
     • Height (H): 6.35cm
   • Volume (V): L×W×H=207.9cm3
   • Density (D): VM​=207.9cm356.88g​=0.2736g/cm3
   • Rounding: Density≈0.274g/cm3