Understanding Physical Properties of Materials: Key Characteristics and Variations

1. Physical Properties(Section 2.2)

2. Physical Properties • Is any characteristic of a material that can be observed or measured without changing the composition of the substances in the material • Viscosity, conductivity, malleability, hardness, melting point, boiling point, and density are examples of physical properties

3. Viscosity • Viscosity is the tendency of a liquid to keep from flowing (its resistance to flowing) • The greater the viscosity, the slower the liquid moves • Thick liquids like corn syrup and honey have a high viscosity • Thin liquids like vinegar and water have a low viscosity • The viscosity of a liquid usually decreases when it is heated

4. Conductivity • A material’s ability to allow heat to flow • Materials that have a high conductivity, such as metals, are called good conductors • If a material is a good conductor of heat it is usually also a good conductor of electricity • Wood is not a good conductor of heat

5. Malleability • Is the ability of a solid to be hammered without shattering • Most metals are malleable • Solids that shatter when struck are brittle

6. Tip of drill is coated in diamond Hardness • One way to compare the hardness of two materials is to see which of the materials can scratch the other • Diamond is the hardest known material

7. Melting & Boiling Points • The temperature at which a substance changes from a solid to a liquid is its melting point • The temperature at which a substance boils is its boiling point (liquid to gas)

8. Density • Is the ratio of the mass of a substance to its volume • Density = Mass Volume • Can be used to test the purity of a substance • Silver has a density of 10.5 g/cm3 at room temperature but if you have a coin with a density of 9.9 g/cm3 at room temperature it must not be pure

9. Using Properties to Identify Materials • Step 1: decide which properties to test • Step 2: do tests on a sample of the unknown • Step 3: compare the results with the data reported for the known materials When a car is involved in a hit-and-run accident detectives use paint chips from the scene of the crime to identify the make and model of the vehicle using a database of the different paint mixtures

10. Using Properties to Choose Materials • People don’t consider just one property when choosing a material for a particular application • Example • You wouldn’t want shoelaces made of wood or steel • Shoelaces need to be flexible, durable, and easy to secure

11. Separating Mixtures • Some properties can be used to separate mixtures • Filtration • Uses a porous barrier to separate a solid from a liquid • Good for heterogeneous mixtures

12. Distillation • Uses differences in the boiling points of the substances involved • Crystallization • Results in the formation of pure solid particles of a substance from a solution containing the dissolved substance

13. Chromatography • Parts of a mixture are separated based on how fast they travel through a medium

14. Recognizing Physical Changes • A physical change occurs when some of the properties of a material change, but the substances in the material remain the same • Change in the state of matter

15. Physical Changes • Crumpling a piece of paper changes the size and shape of the paper and slicing a tomato changes the size and shape of the tomato but it does not change their composition • Some physical changes can be reversed such as melting ice and then freezing it again • Some cannot be reversed (You can’t put the sliced tomato back together and make it whole)