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Class Notes - Unit 1: Chemistry, Matter, and Change Ch. 1 pg. 7-23 and Ch. 2 pg. 39-55 Chemistry is the study of matter. More precisely it is the study of the properties of matter and the changes that matter undergoes. These two major concepts (properties/types of matter and changes) are the focus of this first unit. Matter is anything that 1) takes up space (volume) and 2) has mass. Remember that there is a difference between mass and weight. Mass is the amount of “stuff”- the amount of matter in an object. Weight is the effect of gravity on that amount. Your weight changes when you go between the Earth and the moon because the amount of gravity changes. However, the mass of you on Earth and on the moon is exactly the same because you still have the same overall amount of matter. There aren’t many things that aren’t matter. Even things that you don’t normally think of as being matter actually are. For example, air is matter. It takes up a certain amount of space (volume) and it also has mass (it is made up of carbon dioxide, oxygen, and nitrogen - all things that have mass to them). Chemistry is a subject that studies many facets of the world around us and almost everyone studies chemistry in high school. It is such an important topic to learn because it affects your daily life in so many ways and when you know and understand chemistry you have the ability to control and create many things. There will be a lot of experimentation done throughout this course. Throughout all of our labs it is good to make good detailed observations (recording the facts of what you see) and then use what we learn in this class as well as prior knowledge to infer and draw conclusions as to why what you saw happened. Be careful not to let your inferences cloud your observations. If what you expect to happen for some reason didn’t sometimes that can be just as meaningful; it is important to try and find out and explain why you got different results. Lab Techniques Safety is of paramount importance and should always be in mind in the lab. You should know where the shower, eyewash station, phone, fire blanket, fire extinguisher, and gas shut offs are located in the lab and how/when to use each of them. Remember when a person is on fire, the fire blanket should be used over the fire extinguisher. Another thing to consider in lab is the type of equipment you are using to complete your experiment as well as the size/accuracy of that equipment. To get the mass of a sample, you should use a balance. Zeroing or taring the balance before use will ensure that it is calibrated for you to use. You should not mass chemicals directly on the balance; you should use either weigh paper or glassware. Whatever secondary thing you are using to contain the chemical you are massing (paper or glassware) can be discounted from the overall mass by again pressing the zero or tare button after it has been put on the balance. This is a good habit to form so that you are actually getting numbers of the chemical you are interested in and do not have to remember to subtract out the mass of the paper or glassware. To find the volume of liquids, beakers or graduated cylinders are most typically used. You need to take into consideration the amount and the accuracy of the sample you want to get the volume of. If you only need an approximate amount, a beaker can be used; however, if you need a more specific amount, a graduated cylinder should be used (particularly one close to the size range of what you are measuring). To transfer small amounts of liquid or to more precisely fill a graduated cylinder, a pipet can be used. The plastic disposable pipets hold about 1 mL of liquid. General equipment to transfer chemicals includes spatulas and tweezers for solids and pipettes for liquids. When putting something into a small opening, such as a graduated cylinder or a test tube, you should use a funnel to minimize spills. Use a powder funnel (plastic with a larger opening on the bottom) for solids and a filter funnel (glass) for liquids. To heat things, a Bunsen burner or hot plate can be used. To use a Bunsen burner, be sure that the tubing is snuggly fit on the valve. Make sure you have a lighter that gives you a good, reliable spark. Turn the valve all the way open so that you can hear the gas flowing. Hold the lighter spark side down about an inch over the top of the burner and create a spark. After your flame is lit you can adjust the height of it by adjusting the valve. Most things heated by a Bunsen burner should be suspended over it using a ring stand and the appropriate clamps (ring or test tube). Some things can also be heated by placing them directly on a hotplate. Most of our hotplates also have magnets in them that will stir things placed on top if you add another magnet to what you want stirred. You will be told when to use a burner or a hot plate. In general, you should NEVER put chemicals back into their storage containers for risk of contaminating the entire container. Experiments should be carried out on the higher portion of you lab benches and you should stand during experimentation with your stools pushed in. Unless I tell you otherwise, the chemicals we use in lab are safe to put down the sink as long as you put them down with water. All equipment and benches should be cleaned at the end of every lab. This includes rinsing all glassware with water and hanging them above the sink to dry. Physical and Chemical Properties What’s the best way to describe matter? If you wanted to describe what a penny was, what type of terms would you use? You would describe its properties. Different forms of matter have different properties and it’s those properties that distinguish them. Activity: Describe the properties of your treat. Most properties listed are physical. If you were instead describing a person, would you only describe their size, shape, state of matter, flexibility, etc? No. You would talk about their personalities as well (whether they were kind, etc). Just like people, matter has “personalities” as well. These are known as chemical properties. Physical properties - characteristics of matter that can be observed without changing the object into another type of matter. - Ex: Size, weight, shape, texture, color, flexibility, odor, density, solubility (whether it can dissolve), magnetic, state of matter (whether it is a solid, liquid, or gas), boiling point, melting point Chemical properties - properties that can’t be observed without changing the object into a new substance, a new type of matter - each chemical property describes the matters ability in some way to transform into a new type of matter - Ex: flammability (ability to burn), reactivity (ability to react) No two substances have identical physical and chemical properties. It is the unique set of properties that something has that allows us to distinguish one thing from another. Why is boiling a physical property and not a chemical property? When something boils, it changes its state of matter from a liquid to a gas. It does not change the type of matter that it is. For example, when water boils it changes from liquid water to water vapor but it is still water. For the property to be a chemical property the type of matter has to change. For example, when an iron nail rusts the iron in the nail reacts with the oxygen in the air to form a new substance (the rust, also known as iron oxide). The iron nail therefore has the chemical property of reactivity. Physical Changes A physical change is any change that alters the form or appearance of matter but does not make the matter into a different substance. In a physical change, the substance (the type of matter) is the same before and after the change. There are two common types of physical changes: a change of state and a change of shape. A change of state is a physical change where the state of matter of the substance is changed. The state of matter is whether it is a solid, a liquid, or a gas. This type of change is reversible. For example, if you have a cup of water and you freeze it, it has just changed its state of matter from liquid to solid – it is still water (the same type of matter). When you do the opposite and melt the frozen ice you get the exact same cup of water back that you started with. This change is completely reversible. A change of shape is usually an irreversible change. For example, if you crush an aluminum can you have changed its overall appearance but not the type of matter it is (it’s still just and aluminum can). This type of change is usually irreversible because it is very difficult to get it back into the exact original shape. These types of physical changes are definitely irreversible if it involves cutting or breaking the matter. For example, if you tear a piece of paper, there is no way for it to go back together naturally. Chemical Changes A chemical change is also known as a chemical reaction. A chemical change/reaction is any change that transforms one substance into another substance. It always produces new substances with properties different from the original substances. Chemical changes can also be reversible or irreversible. There are four indicators that a chemical change has occurred: 1) Formation of a solid precipitate upon mixing two solutions. 2) Production of gas bubbles (not due to a physical change such as boiling) 3) Color change (not due to dilution or color mixing) 4) Temperature change (not due to external heating or cooling) It is possible for chemical changes to occur without one of these four indicators being present, however most common chemical changes exhibit at least one of these four. Chemical reactions are represented by chemical equations. A chemical equation is a quick, shorthand notation used to convey as much as possible about what happens in a chemical reaction. Reactants are the general name given to all the elements or compounds that you have before the chemical change has taken place. Products are the general name given for all elements or compounds that you have after the change has occurred. Reactants are shown on the left side of the equation and products are shown on the right side. The reactants and products are separated by an →. This arrow is can be interpreted as “yields”, “produces”, or other words describing the type of chemical change. Reactants → Products If there are more than one reactants or products, they are separated by a + sign. For example, in the reaction between iron and oxygen to produce rust (Fe2O3) the chemical equation is: Fe(s) + O2 (g) → Fe2O3 (s) Another useful piece of information contained in chemical equations can be the states of matter that the reactants and products are in. The four options are: (s) for solid, (l) for liquid, (g) for gas, or (aq) for an aqueous solution (a solid dissolved in water to make a homogeneous mixture). Ex: NaCl(s) = solid table salt NaCl(aq) = a solution of salt water Every chemical reaction obeys the Law of Conservation of Mass (aka the Law of Conservation of Matter). This states that matter is neither created nor destroyed. What this means to us is that whatever mass you start out with is the same amount of mass you end up with. For example, in the above equation if you start with 5 g of Fe and end up producing 6.2 g of Fe2O3 you will have reacted your iron with 1.2 g of O2. Your reactants started with a total of 6.2 g of mass (5+1.2) and your product totaled 6.2 g of mass. The matter was rearranged however the total mass was still the same. Matter/mass is never created or destroyed - it is only rearranged. States of Matter The three states of matter are solid, liquid, and gas. The way that you convert from one state to another is by increasing or decreasing temperature. Temperature is a measure of the amount of heat energy something has. If something has a high temperature is has a lot of energy and the particles move faster and tend to spread out. If something has a low temperature is has a very low energy and the particles move slowly and are often closer together. The state of matter that something is at room temperature all depends on the inherent strength of the forces between the particles in the substance. If the particles have very strong forces between them, the substance will most likely be a solid. If the particles have very weak forces between them, the substance will most likely be a gas. If you look at the particles of a solid, they are very tightly packed in a rigid arrangement. They still have some slight vibrations between the particles however as a whole they have very little movement. They are low energy. Solids have a definite shape and volume because of the tightly packed nature of their particles. The particles in a solid can either be very orderly arranged (to make a crystalline solid) or not arranged in any specific order (to make an amorphous solid). If you look at the particles of a liquid, they are in close contact but not rigidly packed. They have enough space between their particles that they can slide past each other. This is what allows a liquid to flow. Liquids have more energy than solids and it is this energy that makes them be more spread out and faster moving. Liquids have no definite shape and take the shape of whatever container they are in; they do however, have a definite volume and aren’t easily compressed or expanded. If you look at the particles of a gas, they are very far apart and very fast and free moving. Gas particles have a lot of energy (gotten from the temperature increase that is needed to make things in the gas state). Gases have an undefined shape and volume and tend to expand or contract to fill whatever they need to. On a technical note, the term “gas” refers to something that exists in a gaseous state at room temperature (like oxygen, carbon dioxide, etc). For things that are liquids or solids at room temperature, when they are in the gaseous state, they are called “vapor.” For example, water in a gaseous state is referred to as water vapor not water gas. Each of the three states of matter can also be described by the amount of entropy, or disorder, they have in them. In a gas, the particles have a lot of disorder and therefore very high entropy. In a solid, the particles are closely packed together with much more order; therefore they have low entropy. Matter does not change it’s state until all the particles in the sample have gained or lost enough energy to change to another state. This idea is shown in the flat parts of the heating curve (plotting temperature vs. time). Classifications of Matter The properties of matter and the changes that matter undergoes (ie: chemistry) depends on the makeup of the matter. Matter can either be a substance or a mixture. Substances: Elements and Compounds A substance is a single type of mater; matter with a single composition and set of properties. For example: aluminum foil, water, and salt are all substances. No matter where you get your aluminum foil from it is always the same single type of matter – aluminum. Substances can be further classified as either elements or compounds. An element is a pure substance that cannot be broken down into any other substance. Elements are the simplest substances. In your life you see elements all the time (aluminum in aluminum foil, tin in tin cans, the air is nitrogen and oxygen gases. There are over 100 elements currently discovered. All elements are found on the periodic table represented by one or two letter symbols. If it is not on the periodic table, it is not an element. Each element has its own physical and chemical properties. For example, aluminum has very different properties than oxygen. If you take an element and cut it in half and continue cutting it in half until you can’t anymore and have it still have the same properties of that element, then you have an atoms. For example, if you take a solid copper penny and you keep cutting it in half until if you cut it in half once more and it no longer has the properties of copper, then that last size that you have before you lose its properties is an atom. In a solid copper penny, there are approximately 1,000,000 copper atoms. Atoms of different elements have the ability to join. Chemical bonds are the attractive force between two atoms that holds them together. Compounds are pure substances made up of two or more atoms chemically combined in a set ratio. Compounds are represented by a chemical formula (Ex: H2O, CO2). Because a compound has a fixed composition, the formula for a compound is always the same. The subscript in the formula tells the numbers of each atom involved. For example, water (H2O) is two hydrogen atoms combined with one oxygen atom. During chemical bonding, the properties of the substances involved changes. Compounds have properties very separate and distinct from the elements they are made up of. For example, sugar (C11H22O11) is a compound that can be broken down into carbon (ash) and water (H2O). Each of those simpler substances that it is broken down into has very different properties from those of sugar. Sugar Snake: www.metacafe.com/watch/403829/inappropriate_chemistry/ What is the same about elements and compounds? They are both substances; meaning that they both have a fixed, uniform and definite composition. What is the difference between elements and compounds? Whether or not they can be broken down into simpler substances. Can compounds be broken down into simpler substances? Yes. Can elements be broken down into simpler substances? No. Compounds are two or more elements chemically combined (chemically bonded) through chemical reactions and they are broken down into their element components through chemical reactions. What is the ratio of atoms in CO2? There is one carbon atom combined with 2 oxygen atoms. Is CO2 the same as CO? No. CO2 carbon dioxide is the compound we breathe out when we exhale. CO, carbon monoxide, is a deadly gas. That tiny difference of one oxygen atom in the compound makes a big difference in terms of the compound’s properties. Is water an element? What about wood? None of these are elements. They are very commonly used substances, but not elements (not single types of atoms). All elements are listed on the periodic table. Water and wood are compounds, they are different atoms put together in a set ratio. They can all be broken down into elements. For example, water is a compounds and can be broken down into the elements hydrogen (H) and oxygen (O). Salt (NaCl) is a compound and can be broken down into the elements sodium (Na) and chlorine (Cl). Mixtures Most things you encounter, however, aren’t usually a single substance (not just an element or a compound). They are mixtures. Mixtures are two or more substances that are in the same place physically but not chemically combined (not chemically bonded). Each substance has and retains its own set of properties. Is soda a mixture? Yes, there’s water, caffeine, color, flavor, preservatives, etc. Is chicken noodle soup a mixture? Yes, there’s broth, chicken, noodles, vegetables, etc. Is there a difference between these 2 mixtures? Mixtures have variable compositions and when describing a mixture, how the components of a mixture are distributed can be an important piece of information. In the soup, there are distinct parts of the mixture. It is not evenly mixed. One bite you may get a vegetable while another bite you may get a noodle. Any mixture where the composition is not uniform (the components are not evenly mixed together) is known as a heterogeneous mixture. The distinct parts of a heterogeneous mixture are known as phases. A mixture where the composition is uniform is known as a homogeneous mixture. Homogeneous mixtures are also known as solutions. Many solutions we commonly think of are liquid mixtures, however you can also have solutions of gases (ex: air is a homogeneous mixture of nitrogen, oxygen, and carbon dioxide) and solids (ex: stainless steel is a homogeneous mixture of iron, chromium, and nickel). Deciding whether something is a substance or a homogeneous mixture can sometimes be hard. They both appear to only have one type of matter. A good way to determine if something is a mixture is to think if it is possible to have different version of it (different compositions of it). For example, milk is a mixture of many things and we know this because you can get different versions of it (whole, 2%, 1%, skim) where they change the ratios of the components of this mixture. But generally, they are all still classified as “milk.” Separating Mixtures Compounds are held together with chemical bonds and separated into elements based on chemical properties. Mixtures are in the same place physical and are separated into their components based on physical properties. You need to undergo a chemical reaction (a chemical change) to separate compounds into their smaller parts. You only need to physically separate the components of mixtures. The easiest way to separate a mixture is to look at the physical properties of the things involved in the mixture and see if there is one property that is specialized to one part of the mixture that would make it easy to pull out. For example, if you have a mixture of sand, salt, and iron. The iron has the physical property of being magnetic where the sand and salt do not; so running a magnet over the mixture would easily separate out only the iron. To separate mixtures, many physical properties can be used to sort manually or using a specialized machine. These include separating things based on color and texture. In other instances, filters are a tool used to separate mixtures. One of the most common uses of filtration is to separate a solid from a liquid (so the separation is based on the physical property of state of matter). Filters can also be used to separate mixtures based on size, shape, and flexibility. Another common way to separate liquids from a mixture with solids is evaporation. If some of the components of the mixture are magnetic, a magnet can be used to separate a mixture. Solubility, or the ability to dissolve, is also a common physical property used to separate mixtures. It is often combined with another method to fully separate. For example, if you wanted to separate salt from sand. You could add water to dissolve the salt since a physical property of salt is that it is soluble in water. Then the mixture could be filtered, collecting the sand and letting the salt water pass through. Then the salt water could be allowed to evaporate, leaving only the salt behind. Boiling points are also used to separate mixtures. This is particularly useful when trying to separate a mixture of liquids. This process of separating liquids based on their boiling points is known as distillation. In distillation, the mixture of liquids is heated. Once the temperature of the mixture is equal to the boiling point of one of its components, that component will boil and change into a gas. The gas will travel upwards. A cold tube is put in place to collect the gas. When the warm gas hits the cold tube, it condenses and the pure liquid can be collected. Finally, a common physical property used to separate components of a mixture is density.