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You live in a huge universe of matter. Because you cannot live without a sense of order. Our sorting techniques are usually based upon what we can detect with our senses. The characteristics of substances we can note with our physical senses are physical properties. Just as you can recognize your friends by their physical appearance, you can also recognize matter by its physical appearance and properties.
Physical Properties • a property that can be determined without changing the composition of the substance • Examples: color, odor, density, melting point, boiling point
We have studied how to find the density of matter. • As you know, the equation for density is: • density = mass (grams) volume (mL or cm3) mass = density x volume volume = mass density
The following is a list of other ways of telling one form of matter from another. • ductility: The property displayed by certain metals that enables them to be drawn out into wires without breaking • malleability: The property displayed by certain metals that enables them to be hammered, rolled out, shaped, etc. without breaking
hardness: The property of an object that resists being crushed or deformed • brittleness: The property of an object that can easily be broken or crushed into smaller pieces under low pressure • conductivity: The property of metals, some metalloids, and ionic solutions that allow an electric current to pass through them • stateor phase: form – gas, liquid, solid – in which matter is found
solubility: The property of a substance that allows it to dissolve • melting point: The temperature at which a solid changes to a liquid • boiling point: The temperature at which a liquid changes to a gas
The Separation of Matter • If you were to begin your study of chemistry by looking at substances handy to you, you would most likely encounter more mixtures than anything else. In this section, we will discuss several methods for separating mixtures. As you read about each technique, see how many uses you can identify for it. These are the methods in which you will need to be familiar to do the activities later in this course
Method #1: Filtration • is a process of separating large solid particles from a liquid by passing the components through a porous material like filter paper. • Filtrate: The liquid that passes through the porous medium • Residue: the solid material that does not pass through the porous medium
Example • In everyday use, substances are usually filtered to remove undesirable particles. One familiar example of filtration is the purification of water in a swimming pool. This is done by continuously pumping water through the pool's filter. As the water passes through the filters, dirt and any other types of debris that might be harmful are removed. Another example is the filtration of air in heated and air-conditioned buildings. The air is filtered either by a filter on the furnace or in the air intake system in a building in order to cleanse the air impurities.
Method #2: Crystallization • is a process in which crystals are formed by removing the liquid part by evaporation (change from liquid to gas without adding heat) or vaporizing (change from liquid to gas with adding heat)
Example • Salts can be purified by dissolving them in water, filtering the solutions, and then crystallization. The liquid part of the solution is evaporated or heated off and the solid part (salt) remains. Salt has been collected from the world’s oceans for thousands of years using this technique.
Distillation is another important technique used to separate both solid/liquid mixtures and liquid/liquid mixtures. In simple distillation of a solid/liquid mixture, the liquid is removed from the mixture by evaporation and then recollected by condensation.
However, when you have a liquid/liquid mixture, the mixture must be separated by a more complicated technique called fractional distillation. When the mixture of liquids is heated, the liquid with the lowest boiling point is distilled first. This liquid turns into a vapor (gas) and flows out the distillation flask. As it enters the condensing tube, it is cooled and condenses back into a liquid. It is then collected in a graduated cylinder. When the liquid is almost completely evaporated the liquid with the next lowest boiling point begins to distill. This process continues until there is nothing, or only solid impurities, left in the distillation flask.
Method #3: Distillation • is a process of separating a mixture based on different boiling points • Vaporization: a change from liquid to gas at the boiling point when heat is added • Condensation: a change from gas to liquid at the condensation point when heat is removed. • Fraction: each different liquid that is separated out of the mixture
You probably have watched an ink drawing dissolve into a rainbow of colors when water has fallen on it. When an ink drawing comes into contact with water, the water will drag the inkspot with it as it moves across the paper. Some substances in the ink move more slowly than others. We can apply this property to separate the components of the mixture. The result is that the ink separates into different colors.
Method #4: Chromatography • a technique used to separate and analyze various substances in a mixture. The separation occurs because the components are not equally soluble in a solvent and the components are not equal in size.
Chemical Properties of Matter • Chemical Properties: • A property of a substance that is observed when the substance undergoes a change in composition • active: reacts vigorously with other materials • inactive: does not react readily with other materials • inert: do not react under normal or ordinary conditions
Changes in Matter • Now that we have learned the fine points about physical and chemical properties, we are going to look at two kinds of changes – physical changes and chemical changes.
Physical Changes: • refers to a change in appearance not chemical composition of the substance • Examples: phase changes (s-> l -> g), crushing, grinding, dissolving (solubility)
Is tearing a piece of paper a physical change? • YES • Why or why not? • the composition of the matter does not change. It is a change in appearance only.
Is solid water (ice) changing into liquid water a physical change? • YES • Why or why not? • the composition of the matter does not change. It is a change in appearance only.
Chemical Changes • refers to a change in the composition of the matter......a new substance is formed • Examples: rusting of iron , combustion of a candle, burning of gasoline to run a car
There are some key signs that you can look for to determine whether or not a chemical change has occurred. These are as follows:
1. A gas is given off (BUBBLES) but not boiling 2. A precipitate (insoluble solid) is produced..... appears cloudy 3. Water is produced ..... Cobalt chloride paper turns from blue to pink 4. A color change could indicate a chemical change but also may indicate only a physical one 5. A temperature change may indicate a chemical change but can also indicate a physical one
