A physical property is any characteristic of a material that can be observed or measured without changing the composition of the substances in the

Transcription

1 Physical Properties

2 A physical property is any characteristic of a material that can be observed or measured without changing the composition of the substances in the material.

3 Examples of Physical Properties Viscosity, conductivity, malleability, hardness, melting point, boiling point, and density

4 Viscosity The tendency of a liquid to keep from flowing is called its viscosity. Thick liquids, such as corn syrup and honey, have a high viscosity. Thin liquids, such as vinegar and water, have a low viscosity.

5 Conductivity A material s ability to allow heat to flow is called conductivity. Materials that have a high conductivity, such as metals, are called conductors. Good conductors of heat are usually also good conductors of electricity.

6 Hardness One material can scratch another material if it is harder than the other material. A kitchen knife can scratch a copper sheet because stainless steel is harder than copper. The material used to sharpen the knife blade must be harder than stainless steel. Diamond is the hardest known material.

7 Melting and Boiling Points The temperature at which a material changes state is a physical property. The temperature at which a substance changes from solid to liquid (melts) is its melting point. The temperature at which a substance changes from liquid to gas (boils) is its boiling point.

8 Density The ratio of the mass of a substance to its volume is its density. Density can be used to test the purity of a substance. Silver has a density of 10.5 g/cm 3. A coin with a density of 9.9 g/cm 3 is not made from silver, or it contains substances in addition to silver.

9 Density is How closely packed particles in a substance are. Said another way The amount of matter (mass) in a given space (volume). Density = mass (g) volume (cm 3 ) m= 10g m = 10g v = 10cm 3 v = 2cm 3 d= 1g/cm 3 d= 5g/cm 3 LESS DENSE MORE DENSE

10 Density Density = mass (g) volume (cm 3 ) FACTS ABOUT DENSITY MEASURMENTS: Density is found by dividing a mass (g) or (kg) and a volume (cm 3 ) or (ml). Units must also be divided: Example: g/cm 3. Mass = 20g = 2g/cm 3 Volume = 10cm 3

11 Density Density = mass (g) volume (cm 3 ) Given any two of these quantities (density, mass, or volume) you can find the other by either multiplying or dividing appropriately. Density = 2g Volume = 10cm 3 Mass =? = 20g m (2g) x (10cm 3 ) d v Density Triangle

12 Volume of a Solid (square objects, like a box) Volume is the: amount of space something takes up. FACTS ABOUT VOLUME MEASURMENTS: Volume is found by multiplying three distances. Volume = (Length) x (Width) x (Height) Units are also multiplied and become cubed 3 10 m 20 m 10 m Length = 10m Width = 10m Height = 20m (10m) X (10m) X (20m) = 2000m 3

13 Volume of a Liquid FACTS ABOUT LIQUID VOLUME MEASURMENTS: The unit for liquid volume is the Liter (L). Volume is found using a graduated cylinder. Units for small volumes are milliliters (ml). You should always read a graduated cylinder at the bottom of the curve of the liquid. That curve is called the meniscus L = 1000 ml Common Conversions 20 0

14 Mass Mass is the: amount of matter stuff something is made of. Mass will not change unless you add or take away matter. FACTS ABOUT MASS MEASURMENTS: The unit for mass is the gram (g). Large masses are measured in kilograms (kg). A triple beam balance (NOT A SCALE) is used to measure mass. 1 kg = 1000 g Common Conversions

15 Physical Changes

16 Recognizing a Physical Change During a physical change, the state of matter, size and shape of a material can change but not the composition.

17 Recognizing a Physical Change Some examples include: melting butter in a pan crumpling a piece of paper slicing a tomato Some but not all physical changes can be reversed. Braiding hair is a reversible change. Cutting hair cannot be reversed.

18 Chemical Properties

19 Chemical Property A chemical property is any ability to produce a change in the composition of matter. Flammability and reactivity are two examples of chemical properties.

20 Examples of Chemical Properties Flammability is a material s ability to burn in the presence of oxygen. The property that describes how readily a substance combines chemically with other substances is reactivity.

21 Chemical Change

22 How do you know it s a chemical change? Three common types of evidence for a chemical change are a change in color, the production of a gas, and the formation of a precipitate. A chemical change occurs when a substance reacts and forms one or more new substances.

23 A Change in Color A change in color is a clue that a chemical change has produced at least one new substance. The color change in a banana peel is caused by chemical changes that are taking place in the cells of the banana.

24 A Change in Color A new copper roof has a reddish color. The green patina on an old copper roof is a mixture of copper compounds.

25 Production of a Gas When you mix vinegar with baking soda, bubbles of carbon dioxide form immediately. A similar chemical change happens when you use baking powder as an ingredient in a cake recipe. Bubble of carbon dioxide expand and cause the cake to rise.

26 Formation of a Precipitate Any solid that forms and separates from a liquid mixture is called a precipitate. When an acid is added to milk, proteins in the milk undergo a chemical change that causes them to stick together in clumps and form a precipitate cottage cheese.

27 What is the difference between chemical and physical changes? When matter undergoes a chemical change, the composition of the matter changes. When matter undergoes a physical change, the composition of the matter remains the same. Even if you observe a color change, a gas, or a precipitate, you cannot be sure that a chemical change has taken place. When an iron horseshoe is heated, its color changes from gray to red, but the iron is still iron. That means the change is physical, not chemical.