Identify the following combinations as heterogeneous mixtures or homogenous mixtures. The homogeneous mixture appears like a single substance. On the right, the salt crystals have dissolved in the water so finely that you cannot tell that salt is present. Figure 1.4 “Types of Mixtures.” On the left, the combination of two substances is a heterogeneous mixture because the particles of the two components look different. The salt dissolved in water is a homogeneous mixture, or a solution (Figure 1.4 “Types of Mixtures”). On the other hand, if you take salt crystals and dissolve them in water, it is very difficult to tell that you have more than one substance present just by looking-even if you use a powerful microscope. Thus, a combination of salt and steel wool is a heterogeneous mixture because it is easy to see which particles of the matter are salt crystals and which are steel wool. Another word for a homogeneous mixture is solution. A homogeneous mixture is a combination of two or more substances that is so intimately mixed that the mixture behaves as a single substance. It is easy to tell, sometimes by the naked eye, that more than one substance is present. A heterogeneous mixture is a mixture composed of two or more substances. Physical combinations of more than one substance are called mixtures. We frequently encounter objects that are physical combinations of more than one element or compound. Examples of compounds include water, penicillin, and sodium chloride (the chemical name for common table salt).Įlements and compounds are not the only ways in which matter can be present. There are over 50 million compounds known, and more are being discovered daily. The physical and chemical properties of a compound are different from the physical and chemical properties of its constituent elements that is, it behaves as a completely different substance. ![]() Examples of elements include iron, carbon, and gold.Ī compound is a combination of more than one element. (The other elements are radioactive, a condition we will consider in Chapter 15 “Nuclear Chemistry”.) Each element has its own unique set of physical and chemical properties. There are about 115 elements known to science, of which 80 are stable. An element is the simplest type of chemical substance it cannot be broken down into simpler chemical substances by ordinary chemical means. Here, we will use the term substance with its strict chemical definition.Ĭhemistry recognizes two different types of substances: elements and compounds. The definition of the term substance is an example of how chemistry has a specific definition for a word that is used in everyday language with a different, vaguer definition. Sometimes the phrase pure substance is used, but the word pure isn’t needed. Water is warmed to make a cup of coffee.Ī sample of matter that has the same physical and chemical properties throughout is called a substance.Identify each process as a physical change or a chemical change. ![]() (In fact, a lot of cooking involves chemical changes.) Because of the oven’s temperature, chemical changes are occurring in the bread dough to make fresh bread.Because the water is going from a gas phase to a solid phase, this is a physical change.Bread dough becomes fresh bread in an oven.In the following chapters, we will see how descriptions of physical and chemical properties are important aspects of chemistry.ĭescribe each process as a physical change or a chemical change. Does it behave violently when put in water? This reaction is a chemical property as well (Figure 1.2 “Chemical Properties”). Does a sample of matter burn? Burning is a chemical property. Figure 1.2 “Chemical Properties.” The fact that this match burns is a chemical property of the match.Ĭhemical properties are characteristics of matter that describe how matter changes form in the presence of other matter. The three fundamental phases of matter are solid, liquid, and gas (see Figure 1.1 “The Phases of Matter”). An important physical property is the phase (or state) of matter. Some of many physical characteristics of matter are shape, color, size, and temperature. Physical properties are characteristics that describe matter as it exists. There are two basic ways to describe matter: physical properties and chemical properties. To understand matter and how it changes, we need to be able to describe matter. The invention itself may be matter, but the idea for it is not.įigure 1.1 “The Phases of Matter.” Chemistry recognizes three fundamental phases of matter: solid (left), liquid (middle), and gas (right).A tree has mass and takes up space, so it is matter.Love is an emotion, and emotions are not matter.A hot dog has mass and takes up space, so it is matter. ![]() Note how the mass units cancel, leaving the volume unit, which is what we are looking for.Which of the following is matter and not matter?
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