General-Chemistry-Lecture-Notes.pdf

General Chemistry Lecture (Prelim)  SI unit o Units: “King Henry Doesn’t Usually Drinking Chocolate Milk”  King = Kilo-  Drinking = Deci-  Henry = Hecto-  Chocolate = Centi-...

General Chemistry Lecture (Prelim)  SI unit o Units: “King Henry Doesn’t Usually Drinking Chocolate Milk”  King = Kilo-  Drinking = Deci-  Henry = Hecto-  Chocolate = Centi-  Doesn’t = Deca-  Milk – mili-  Usually = Unit o Common Devices for measurements:  Length = meter stick or scale  Volume = buret, pipette, graduated cylinder and the volumetric flask  Mass = Balance  Temperature = thermometer o Reading volume: Use graduated cylinder  Place the graduated cylinder in a flat surface.  Read the meniscus (it is the curved surface of liquid) at the eye level  For transparent liquid read the bottom meniscus  For opaque liquid, read the top meniscus  Sources of Error when reading the Volumetric Glasswares  Parallax error – read the meniscus at eye level. o Eye level above the meniscus – lower reading than true value o Eye level below the meniscus – higher reading than the true value  Air bubbles at the tip o Triple Beam Balance   Beams in the Triple Beam Balance  The maximum weight a triple beam balance can measure is 600 grams.  The first beam can measure up to 10 grams.  The second beam can measure up to 500 grams, read in 100 g increments.  The third beam can measure up to 100 grams, read in 10 g increments.  Each beam has notches (e.g., grooves) for the weights. You must use them; otherwise you will not be able to record accurate measurements. o Before Weighing  Check if the pans are clean  Before you weigh something, ‘zero‘ the balance. Do this by sliding back all the weight poises (that slide along the beams) so that the pointer is right at the zero line. You might need to turn the zero adjustment knob a little bit to get it right at the line. o Adjusting the Platform Balance  If the pointer swings more to the above of the zero line , turn adjuster clockwise until pointer is pointer is at zero  If pointer swings more to the below of the zero line, turn adjuster counterclockwise until pointer is pointer is at zero o Measuring Mass by Weighing by Difference  When you set an object on the balance platform, the pointer immediately goes up and is no longer zeroed. To find out the weight of the obje ct, you’ll need to slide the weight poises until the pointer is at zero again. Start with the two heavier weight poises and then use the lightest one to do the fine tuning.  Example: Measuring the contents in the beaker  Measurement #1: Mass of the beaker with contents = 125 g,  Measurement #2: Mass of the beaker: 75g  Mass of Content: 125 g – 75 g = 50 g  Measuring solid with weighing by difference  Measure the mass of the paper first  Apply the contents on the paper, measure the mass of the paper with the content.  Example: Measure the mass of Salt  Mass of paper with contents: 30g  Mass of paper: 5g  Mass of Salt: 30 g – 5 g = 25g  The Bunsen Burner  It is used as a source of heat and energy in the laboratory  Note: Adjust the height of flame in the gas valve to 8-12 cm o Luminous and Non-luminous flame o Types of Burner  Tirril - The Tirrill burner is an air and gas device much like the Bunsen, but with extra adjustments that provide for better temperature control and flame size.  Bunsen - The Bunsen burner is the simplest of the laboratory burners available. It takes little maintenance and has been used in labs all over the world for more than a century  Meker - A Meker burner is also similar in design, but it is larger and works best for experiments that require high temperatures. The Meker has more openings to provide an enhanced mix of gas and air, and the tube is wider and covered with a wire grid that separates the flame into smaller flames for better distribution of heat.  What is Matter? o physical material of the universe; anything that has mass and occupies space o States of Matter  Classification of matter  o Pure Substance vs Mixture  A pure chemical substance is any matter that has a fixed chemical composition and characteristic properties  Oxygen, for example, is a pure chemical substance that is a colorless, odorless gas at 25°C  Mixtures, which are combinations of two or more pure substances in variable proportions in which the individual substances retain their identity o Homogeneous Mixture  If all portions of a material are in the same state, have no visible boundaries, and are uniform throughout, then the material is homogeneous.  Homogeneous mixtures are also called solutions  Although most solutions we encounter are liquid, solutions can also be solid.  Solid solutions of two or more metals are commonly called alloys  Example: Air, Tap Water, and Alloys o Heterogeneous Mixture  If the composition of a material is not completely uniform, then it is heterogeneous  Mixtures that appear to be homogeneous are often found to be heterogeneous after microscopic examination. This refer as Colloid  Milk, for example, appears to be homogeneous, but when examined under a microscope,  A suspension mixture is a type of heterogeneous mixture that contains relatively large sized particles. These particles can be visually identified in the suspension mixture, in which their particle settle down on standing o Tyndall Effect  Tyndall effect is the property of colloids to scatter light in all direction  Properties of Matter o Physical - observed without changing the identity and composition of the substance.  A physical property is an attribute of matter that is independent of its chemical composition.  Chemical - describes the way a substance may change, or react, to form other substances. A physical property is an attribute of matter that is independent of its chemical composition.  Intensive and Extensive Property of Matter Intensive properties of matter – An intensive property is a bulk property, which means it is a system’s local physical property that is independent of the system’s size or volume of material. Intensive properties are those that are independent of the amount of matter present. Pressure and temperature, for example, are intensive properties.  Extensive property of matter – A property that is dependent on the amount of matter in a sample is known as an extensive property. Extensive properties include mass and volume. The scale of the system or the volume of matter in it determines the extensive property of the system. Extensive properties are those in which the value of a system’s property is equal to the sum of the values for the parts of the system.  Other Important Physical Properties  Luster defined as the way it reacts to light.  Malleability means that it can deform under an amount of stress.  Ductility ability to be drawn into a thin wire  Density determine if an object will also determine whether it will sink or float in a particular chemical o Chemical Property  Reactivity - The tendency of matter to combine chemically with other substances is known as reactivity. Certain materials are highly reactive, whereas others are extremely inactive. Potassium, for example, is extremely reactive, even in the presence of water. A pea-sized piece of potassium reacts explosively when combined with a small volume of water.  Flammability - The tendency of matter to burn is referred to as flammability. As matter burns, it reacts with oxygen and transforms into various substances. A flammable matter is anything like wood.  Toxicity - Toxicity refers to the extent to which a chemical element or a combination of chemicals may harm an organism.  Acidity - A substance’s ability to react with an acid is a chemical property. Some metals form compounds when they react with different acids. Acids react with bases to create water, which neutralizes the acid.  Physical and Chemical Change Physical Change Chemical Change When a substance undergoes a When a substance undergoes a chemical physical change, its composition change, its molecular composition is changed remains the same despite its molecules entirely. Thus, chemical changes involve the being rearranged. formation of new substances. Physical change is a temporary A chemical change is a permanent change. change. A Physical change affects only physical Chemical change both physical and chemical properties i.e. shape, size, etc. properties of the substance including its composition A physical change involves very little to During a chemical reaction, absorption and no absorption of energy. evolution of energy take place. Some examples of physical change are A few examples of chemical change are freezing of water, melting of wax, digestion of food, burning of coal, rusting, etc. boiling of water, etc. Generally, physical changes do not Chemical changes usually involve the involve the production of energy. production of energy (which can be in the form of heat, light, sound, etc.) In a physical change, no new A chemical change is always accompanied by substance is formed. one or more new substance(s). Physical change is easily reversible i.e Chemical changes are irreversible i.e. original original substance can be recovered. substance cannot be recovered. o Physical Change  The changing of color of a substance is not necessarily an indicator of a chemical change. For example, changing the color of a metal does not change its physical properties. However, in a chemical reaction, a color change is usually an indicator that a reaction is occurring. Painting the metal car does not changing the composition of the metallic substance.  Temperature  Although we cannot see temperature change, unless if a change of state is occurring, it is a physical change.  One cannot see the pan physically changing shape, color, texture, or any of the other physical properties. However, if one were to touch the pan, it would be incredibly hot and could cause a burn. Sitting idle in a cupboard, this pan would be cold.  Shape  The shape of an object can be changed and the object will still remain true to its chemical composition. For example, if one were to fold money, as shown by the figure below, the money is still chemically the same.  Change of State  The change of state is likewise a physical change. In this scenario, one can observe a number of physical properties changing, such as viscosity and shape. As ice turns into water, it does not retain a solid shape and now becomes a viscous fluid. The physical "reaction" for the change of ice into liquid water is:  H2O(s)→ H2O(l)  The following are the changes of state: o If heat is added to a substance, such as in melting, vaporization, and sublimation, the process is endothermic. In this instance, heat is increasing the speed of the molecules causing them move faster. o The following are the changes of state: o If heat is removed from a substance, such as in freezing and condensation, then process is exothermic. In this instance, heat is decreasing the speed of the molecules causing them move slower. o Chemical changes  Change in Temperature  In a chemical alteration, the temperature change occurs as a result of the breaking or formation of chemical bonds.  When the chemical bonds of the reactants are broken, sometimes excess energy is released, causing heat to be discharged, and leading to an increase in temperature. o Burning wood is an example of a reaction that releases excess energy as heat.  Alternatively, a reaction may require energy from the environment in order to take place, causing heat to be absorbed, and leading to a decrease in temperature. o A chemical cold pack in a first aid kit is an example of a chemical reaction that absorbs heat energy resulting in cooling.  Change in Color  A change in color is also another characteristic of a chemical reaction taking place. For example, if one were to observe the rusting of metal over time, one would realized that the metal has changed color and turned orange. This change in color is evidence of a chemical reaction. However, one must be careful; sometimes a change in color is simply the mixing of two colors, but no real change in the composition of the substances in question.   4Fe+3O2+6H2O→4Fe(OH)3  Noticeable Odor  When two or more compounds or elements are mixed and a scent or odor is present, a chemical reaction has taken place. For example, when an egg begins to smell, (a rotten egg) a chemical reaction has taken place. This is the result of a chemical decomposition  Formation of a Precipitate  The formation of a precipitate may be one of the most common signs of a chemical reaction taking place. A precipitate is defined to be a solid that forms inside of a solution or another solid. Precipitates should not be confused with suspensions, which are solutions that are homogeneous fluids with particles floating about in them. For instance, when a soluble carbonate reacts with Barium, a Barium Carbonate precipitate can be observed.  Formation of Bubbles  The formation of bubbles, or rather a gas, is another indicator of a chemical reaction taking place. When bubbles form, a temperature change could also be taking place. Temperature change and formation of bubbles often occur together. For example, in the following image, one can see a gas spewing. This is the formation of a gas.  Na2CO3 (aq)+2HCl(aq)→ 2NaCl (aq) +H2O (l) +CO2 (g)  Separation Techniques o Decantation  A process whereby the solid particles are allowed to settle first to the bottom of the container and then the liquid portion is being poured out.  Solid Portion = Residue (it is being retained)  Liquid Portion = Decantate (it is being poured out) o Filtration  The process of separating solid particles from liquid by pouring the mixture through the filter paper.  Useful for separating heterogeneous mixture where solid particles is observed in a liquid or gaseous medium, or by the product of precipitation  Filtrate = Liquid portion  Residue = Solid Portion  How to fold a filter paper?  o Precipitation  The soluble substances is separated from a solution as a solid by means of chemical reagent.  Precipitant = liquid portion  Precipitate = solid portion  𝑁𝑎𝐶𝑙 (𝑎𝑞) + 𝐴𝑔𝑁𝑂 (𝑎𝑞) →→ 𝐴𝑔𝐶𝑙(𝑠) + 𝑁𝑎𝑁𝑂 (𝑎𝑞) o Evaporation  A process wherein molecules escape from the surface of a liquid, vaporizes in air.  Useful if collecting solid residue from a liquid solution.  It involved three kinds of evaporation:  Direct Evaporation – Involves heating. (Direct Fire)  Indirect Evaporation – Direct involvement of fire but using waterbath for the samples to be evaporated.  Spontaneous Evaporation – without the application of heat – usually done for volatile solvents o Distillation  Process wherein substances are miscible and they can be separated due to their differences in boiling point.  Useful if collecting liquid sample from a solution.  Involves the process of evaporation and condensation  Example: Boiling point of Acetone and Water  Acetone = 56C  Water = 100C  Magnetization o Process of separating, two solid particles, where one substance is attracted to magnet and the other is not.