Learn more. Can I identify an unknown substance measuring density and calomimetric data? Asked 6 years, 1 month ago. Active 5 years ago. Viewed 2k times. Improve this question. Klaus-Dieter Warzecha Imagine Dragons Imagine Dragons 1 1 silver badge 10 10 bronze badges. Do you want to identify the substance using laboratory methods, or by thermodynamic properties, or something else?
You can identify an unknown substance by measuring its density and comparing your result to a list of known densities. Assume that you have to identify an unknown metal. You can determine the mass of the metal on a scale. You can determine the volume by dropping the object into a graduated cylinder containing a known volume of water and measuring the new volume.
You divide the mass by the volume and compare the density to a list of known densities. A metal bolt with a mass of Lead a discussion about why the copper cube has a greater mass than the aluminum cube. Ask students: How can two objects, which are exactly the same size and shape, have a different mass? Help students understand that the difference in mass must have something to do with the atoms in each cube. There are three possible explanations about the copper and aluminum atoms in the cubes that could explain the difference in mass.
Copper atoms might have more mass than aluminum atoms. Copper atoms might be smaller so more can fit in the same volume.
Copper and aluminum atoms might be arranged differently so more copper atoms fit in the same size cube. Give each student an activity sheet. Project an illustration and use the pictures of the copper and aluminum atoms to introduce the concept of density. Show students the image Aluminum and Copper Atoms Point out that the copper atoms are slightly smaller than aluminum atoms.
Show animations and demonstrate how to measure volume and mass of a cube. Show the animation Cube. Volume The cubes are 2. Show students that in order to calculate the volume, you multiply the length 2. Rounding this number to Record the volume of the cube in cubic centimeters cm 3.
Mass Demonstrate how to use the balance that students will be using to measure the mass of the cube. Record the mass of the cube in grams g. Density Show students how to calculate density by dividing the mass by the volume. Explore Have students calculate the density of eight different cubes and use the characteristic property of density to correctly identify them. Question to investigate Can you use density to identify eight cubes made of different materials?
Materials for the class Set of eight cubes of equal volume Calculator Teacher preparation Use a piece of masking tape and a permanent marker to mark the eight cubes with the letters A—H.
Materials for each group Cubes marked A—H that you will share with other groups Balance that can measure in grams Calculator Procedure The volume of each cube is given in the chart. It is Find the mass in grams of each cube using a scale or balance. Record this mass in the chart. Trade cubes with other groups until you have measured the mass of all eight cubes. Table 1. Approximate densities for various materials. Write the name of the material in your chart for cubes A—H.
Explain Discuss how the mass, size, and arrangement of atoms and molecules affect the densities of metal, plastic, and wood Explain to students that each substance has its own density because of the atoms and molecules it is made from.
Metal Project the image Metal Most common metals like aluminum, copper, and iron are more dense than plastic or wood. The atoms that make up metals are generally heavier than the atoms in plastic and wood and they are packed closer together.
The difference in density between different metals is usually bsed on the size and the mass of the atoms but the arrangement of the atoms in most metals is mostly the same. Also, how do you identify a substance? These properties are classified as physical properties and chemical properties. Physical properties are those that can be determined or measured without changing the composition or identity of the substance.
These properties include color, odor, taste, density, melting point, boiling point, conductivity, and hardness. When might you come into contact with unknown chemicals in the real world? Simple tests you can do. Chromatographic methods. Spectroscopic methods. X-Ray crystallography a. X-ray diffraction, or XRD Mass spectrometry. Density can be useful in identifying substances.
It is also a convenient property because it provides a link or conversion factor between the mass and the volume of a substance. Mass and volume are extensive or extrinsic properties of matter - they depend on amount.
So Pure materials ,they can not have same densities. Assuming they are not isotopes of each other. But mixtures, compounds or different phases can have same densities.
Heating a substance causes molecules to speed up and spread slightly further apart, occupying a larger volume that results in a decrease in density. Cooling a substance causes molecules to slow down and get slightly closer together, occupying a smaller volume that results in an increase in density. The simplest way to use the periodic table to identify an element is by looking for the element's name or elemental symbol.
The periodic table can be used to identify an element by looking for the element's atomic number. The atomic number of an element is the number of protons found within the atoms of that element.
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