TOPIC 2 INTRO TO CHEM FOR ENGR.pdf

INTRODUCTION TO CHEMISTRY FOR ENGINEERS What are soda cans made of ? ▪ How Chemistry and Engineering helped transform aluminum into an inexpensive structural material ▪ The Study of Chemistry ▪ The Science of Chemistry: Observations and Models ▪ Numbers and Measurements in Chemistry ▪...

INTRODUCTION TO CHEMISTRY FOR ENGINEERS What are soda cans made of ? ▪ How Chemistry and Engineering helped transform aluminum into an inexpensive structural material ▪ The Study of Chemistry ▪ The Science of Chemistry: Observations and Models ▪ Numbers and Measurements in Chemistry ▪ Problem Solving in Chemistry and Engineering ▪ Material Selection and Bicycle Frames What makes aluminum an attractive material for making soda cans? ✔ light but fairly strong ✔ aluminum can is much lighter than tin or steel can ✔ the can does not add much weight compared to the soda itself, so the can are easier to handle and cheaper to ship. ✔ does not readily undergo chemical reactions that might degrade it as the cans transported and stored widespread availability of aluminum collaboration between the basic science of chemistry and the applied sciences of engineering  In 19th century, aluminum was a rare an precious material. In Europe, Napoleon was emperor of a sizable portion of the continent, and he would impress guests by using extravagant aluminum tableware.  the capstone at the top of the Washington Monument is aluminum Weighing in at 100 ounces, the capstone of the monument was the largest single of pure aluminum ever cast at that time Why was aluminum so expensive then, and what changed to make it so affordable now? ▪Society has needs for goods and materials. ▪The raw materials needed to make these goods must somehow be extracted from the earth. ▪When the goods are used up, the leftovers become waste that must be disposed of, completing the cycle by returning the exhausted materials to the ecosystem. Role of engineering in this cycle: ✔ maximize the efficiency with ✔ minimize the amount of which materials are extracted waste that is returned  Aluminum occurs in an ore, called BAUXITE (composed of useless rock and aluminum in combination with oxygen) Before aluminum can be used in our soda can, it must first be extracted from its ore and purified. BAUXITE THE STUDY OF CHEMISTRY CHEMISTRY ▪the central science ▪important to so many fields of scientific study ▪help you appreciate the chemical viewpoint and the way it can help you to understand the natural world Three Levels of Understanding on the Nature of Chemistry 1. MACROSCOPIC PERSPECTIVE When we observe chemical reactions in the laboratory or in the world around us, we are observing matter at the macroscopic level. When we study chemistry, we need to be aware that some of what we observed in nature is not matter. For example, light is not considered matter because it has no mass.  One of the most common ways to observe matter is to allow it to change in some way. Two Types of Changes: 1. PHYSICAL CHANGE 2. CHEMICAL CHANGE PHYSICAL PROPERTIES ▪ Variables that we can measure without changing the identity of substance being observed ▪ MASS and DENSITY object given and some standard ▪ Mass –measured by using balance ▪ Density – a ratio of mass to volume ▪ also include color, viscosity, hardness, and temperature ▪ Other physical properties are heat capacity, boiling point, melting point, and volatility CHEMICAL PROPERTIES are associated with the types of chemical changes that a substance undergoes. For example, some materials burns readily whereas other do not. Burning in oxygen is a chemical reaction called COMBUSTION CORROSION – the degradation of metals in the presence of air and moisture. ability of paint to prevent corrosion can be determined only by observing how a substance changes its identity in chemical reactions  Both chemical and physical properties of aluminum are important to its utility MALLEABILITY – a measure of a material’s ability to be rolled or hammered into thin sheets - is a physical property because the substance remains intact – it is still the same metal, just in a different shape - Aluminum can is formed during its manufacturing process, but its shape can be changed, you may crush it then put in a recycle bin  Chemical Property of Aluminum Pure aluminum would react with the acids in many popular soft drinks Aluminum cans are coated inside with a thin layer of polymer –a plastic – to keep the metal from reacting with the contents Three Common States or Phases When we observe chemical reactions macroscopically, we encounter three common states or phases: SOLID, LIQUID and GAS 1. SOLIDS –At macroscopic level, solids are hard and do not change their shapes easily. When a solid is placed in a container, it retains its own shape rather than assuming that of the container. 2. LIQUIDS – adapt to the shape of the container in which they are held 3. GASES – expands to occupy the entire volume of its container Aluminum that we encounter daily is a solid, but during the refining process, the metal must become molten, or liquid. Handling the molten metal, pouring it into containers, and separating impurities provide both chemical and engineering challenges for those who design aluminum production plant. 2. MICROSCOPIC OR PARTICULATE PERSPECTIVE We consider the particles that make up matter All matter is composed of atoms and molecules In many cases, the matter we encounter is a complex mixture of chemicals, and we refer to each individual component as chemical substance. All matter comprises a limited number of building blocks called elements.  Atoms – are unimaginably small particles that cannot be made any smaller and still behave like chemical system When we study matter at levels smaller than an atom, we move into nuclear or elementary particle physics. But atoms are the smallest particles that can exist and retain the chemical identity of whatever element they happen to be.  Molecules – are groups of atoms held together so that they form a unit whose identity is distinguishly different from atoms alone Chemical bonds attractive forces responsible for holding the atoms together in molecules  This perspective provides a more detailed look at the distinction between chemical and physical changes. Because atoms and molecules are far too small to observe directly or to photograph, typically we will use simplified, schematic drawings. Often, atoms and molecules will be drawn as spheres to depict them and consider their changes. 3. SYMBOLIC REPRESENTATION The third way that chemist perceive their subject is to use symbols to represent the atoms, molecules, and reactions that make up the science. The symbolic representation of water H2O Symbolic level of understanding provides a way to discuss some most abstract parts of chemistry We need to think about atoms and molecules, and the symbolic representation provides a convenient way to keep track of these particles we’ll never actually see. Al Aluminum oxide in Bauxite Pure Aluminum THE SCIENCE OF CHEMISTRY: OBSERVATION AND MODELS Chemistry -> an empirical science We study chemistry by measuring properties of chemical substances and observing chemical reactions Once observations have been made, models are created to help organize and explain the data Observation in Science Why observations in chemistry are made? Observations are made because materials with certain properties are needed. Example: containers that hold liquids such as soft drinks need to be strong enough to hold the liquid but light in weight so they don’t increase the cost of transporting the product too much Before steel can were the containers that society demanded. But steel is relatively heavy, so there was an incentive to find a different packaging material. Scientists and engineers worked together to make observations that confirmed the desirability of aluminum for this use. ACCURACY AND PRECISION A. Accurate and Precise B. Accurate and not precise C. Not accurate and precise D. Not accurate and not precise ACCURACY AND PRECISION Because we cannot observe nature with complete certainty, we need to establish the type of uncertainty we encounter in making observations. To do this, two terms are used: ACCURACY AND PRECISION ACCURACY indicates how close the observed value is to the true value. PRECISION is the spread in values obtained from the measurement. RANDOM ERROR AND SYSTEMATIC ERROR Error in measurement is unavoidable. Characteristics of error fall into categories: 1. RANDOM ERROR 2. SYSTEMATIC ERROR SYSTEMATIC ERROR RANDOM ERROR -> is predictable and either constant or proportional -> If you take multiple measurements, the values to the measurement cluster around the true value -> primarily influence a measurement's accuracy -> primarily affects precision. Examples: -> affects the last significant digit of a measurement. 1. Forgetting to tare or zero a balance produces Examples: mass measurements that are always "off" by 1. When weighing yourself on a scale, you position the same amount. An error caused by not yourself slightly differently each time. setting an instrument to zero prior to its use is 2. When taking a volume reading in a flask, you called an offset error. may read the value from a different angle each 2. Not reading the meniscus at eye level for a time. volume measurement will always result in an 3. Measuring your height is affected by minor inaccurate reading. posture changes. 3. Measuring length with a metal ruler will give a different result at a cold temperature than at a hot temperature, due to thermal expansion of the material. Interpreting Observations TWO TYPES OF REASONING: 1. Inductive Reasoning - Begins with a series of specific observations and attempts to generalize to a larger, more universal conclusion. EXAMPLE: We have asserted that all gases expand to occupy the full volumes of their containers. This universal conclusion was first drawn by inductive reasoning based on observations of many different gases under many different conditions. 2. Deductive Reasoning -takes two or more statements or assertions and combines them so that a clear and irrefutable conclusion can be drawn. EXAMPLE: Consider the developments that led to the affordable refining of aluminum. Even in the 19th century, aluminum ore was available. Metallurgists and other scientists were aware that the combination of aluminum with oxygen in ores is very stable. Observations allowed them to reduce that the chemical bonding forces in the alumina must be strong and would be difficult to overcome. Initial schemes for refining the metal involved heating and adding materials, such as carbon, that would react with oxygen that might be liberated. MODEL IN SCIENCE To organize this vast amount of information, scientists create models and theories to make sense of a range of observations. MODEL – refers to a largely empirical description, such as the fact that gas pressure is proportional to temperature IMPORTANCE 1. They allow us to summarize a large number of observations concisely. 2. They allow us to predict behavior in circumstances that we haven’t previously encountered 3. They represent examples of creative thinking and problem solving 4. Constructing and refining models can lead us ultimately to a more fundamental understanding of a problem.  THEORY – an explanation that is grounded in some more fundamental principle or assumption about the behavior of a system. LAWS - are theories that become so sufficiently refined, well tested, and widely accepted that they come to be known NUMBERS AND MEASUREMENTS IN CHEMISTRY Chemistry - an experimental science that requires the use of a standardized system of measurements. MEASUREMENT - a collection of quantitative or numerical data that describes a property of an object or event. A measurement consists of two parts: 1. the amount present or numeric measure, and 2. the unit that the measurement represents within a standardized system. The internalization of science and engineering led to the establishment of a standard system that provides the needed flexibility to handle a wide array of observations. By international agreement in 1960, scientists around the world now use International System of Units or SI Units (Système International d'Unités) that are based on the metric system of measurements. SI defined UNITS as combined set of prefixes that designate powers of ten. When observations are reported in this system, the base unit designates the type of quantity measured. EXAMPLE: we can immediately recognize any quantity reported in meters (m) as a distance. BASE QUANTITIES OF THE SI SYSTEMS OF UNITS PROPERTY UNIT, WITH ABBREVIATION Mass kilogram, kg Time second, s Distance meter, m Electric current ampere, A Temperature Kelvin, K Number of particles mole, mol Light Intensity candela, cd  Not every quantity can be measured directly in terms of just the seven base units. Some units comprised combinations of these base units. DERIVED UNITS –units comprised of combination of base units Example: Joule (J) 1 J = 1 kg m2/s2  Chemists also use a wide variety of units to describe concentration, which measures how much of a particular substance is present in mixture. Metals often contain minor impurities, and in some cases the units used are simply percentages; other used include parts per million (ppm) and part per billion (ppb) ppm (parts per million) tells how many particles of particular substance are present for every 1, 000, 000 particles in the sample. ppb – the sample size is one billion particles. TEMPERATURE degrees Fahrenheit, degrees Celsius, Kelvin temperature scale can be measured using thermometer. The familiar Fahrenheit scale originally chose body temperature as one reference and set it to 100oF. The second reference point was the coldest temperature that could be achieved by adding salt to ice water, a practice that lowers the melting point of ice.  This established 0oF, and the temperature range between the two points at 32oF and the boiling of water at 212oF. The Celsius scale was developed in a similar way, but with the freezing of pure water set at 0oC and the boiling point at 100oC. Conversions between temperature scales Celsius to Fahrenheit: o F = (1.8 x oC ) + 32 Fahrenheit to Celsius: o C = (oF – 32)/ 1.8 Kelvin to Celsius: o C = K – 273.15 Celsius to Kelvin K = oC + 273.15 Engineers in some disciplines use the Rankine temperature scale (0R), which is an absolute scale whose degrees are the same size as those of the Fahrenheit scale. PRACTICE EXERCISE: A.) Express 275oC in K and oF. B.) Express 138K in oC. C.) Express -47.0 oF in K. Numbers and Significant Figures Scientific Notation - used to express very small and very large numbers Example: Pesticide production in the world exceeds millions of tones, whereas pesticide residues that may harm animals or humans can have masses as small as nanograms. Significant Figures When numbers are derived from observations of nature, we need to report them with the correct number of significant figures. are used to indicate the amount of information that is reliable when discussing a measurement. RULES FOR SIGNIFICANT FIGURES IN NUMBERS REPORTED FROM SCIENTIFIC OBSERVATION: 1. When a zero establishes the place for the decimal in the number, it is not significant. e.g. 51300 m and 0.043 g 2. A zero is significant when it is the final digit after a decimal or when it is between other significant digits. e.g. 4.30 mL and 304.2 kg PRACTICE EXERCISE 1.) An alloy contains 2.05% of some impurity. How many significant figures are reported in this value? 2.) How many significant figures are reported in each of the following measurements? A. 0.000403 s B. 200, 000 g  We need to account for significant figures in assessing values that we obtain from calculations. The general principle is that the calculated value should be reported with a number of significant figures that is consistent with the data used in the calculations. Three key rules required to determine the number of significant figures in the result of calculations. RULE 1: For multiplication and division, the number of significant figures in a result must be the same as the number of significant figures in the factor with the fewest significant figures. 0.24 kg x 4621 m = 1109.04 kg m Correctly reported SF -> 1100 kg m or 1.1x103 kg m RULE 2: For addition and subtraction, the rules for significant figures center on the position of the first doubtful digit rather than on the number of significant digits. The result should be rounded so that the last digit retained is the first uncertain digit. If the numbers added or subtracted are in scientific notation with the same power of 10, this means that the result must have the same number of digits to the right of the decimal point. 4.882 m + 0.3 m = 5.182 m Should be reported as -> 5.2 m RULE 1 and 2 apply to any numbers that result from most of the measurements that we make take. But in the special case of countable objects, we must consider RULE 3: RULE 3: When we count discrete objects, the result has no ambiguity. Such measurements use exact numbers, so effectively they have infinite significant figures. Thus if we need to use information such as four quarts in a gallon or two hydrogen atoms in a water molecule, there is no limitation on significant figures. PRACTICE EXERCISE: A.) 4.30 x 0.31 = B.) 4.033 + 88.1 = C.) 5.6/ 1.732 x104 = PROBLEM SOLVING IN CHEMISTRY AND ENGINEERING Calculations play a major role in the practice of chemistry and in its application to real world issues and problems. Engineering designs routinely rely on tremendous number of calculations. To a chemist, the questions associated with aluminum ore require looking into the nature of chemical bonding and how to overcome the stability of strong bonds between aluminum and oxygen. To an engineer, the problems to be addressed in refining the ore might focus on how to deliver enough electricity when and where it is needed. USING RATIOS We encounter and use ratios regularly. We discuss the speed of our cars. When we form the ratio and carry out the indicated arithmetic, the result tells us how much of the numerator is equivalent to one unit if the denominator. A/B (tells how much A is in one unit of B) B/A (tells how much B is in one unit of A)  DIMENSIONAL ANALYSIS OR FACTOR-LABEL METHOD We use ratios in a variety of common calculations in chemistry. One that you will undoubtedly also encounter in engineering is the need to convert between units if different sizes. PRACTICE EXERCISE: Visible light is commonly described in terms of its wavelength, which is usually given in units of nanometers. In subsequent calculations, this measurement often needs to be expressed in units of meters. If we considering orange light of wavelength 615 nm, what is its wavelength in meters? 1 m = 1 x 109 nm CONCEPTUAL CHEMISTRY PROBLEMS To ensure that the concepts involved in chemistry are understood, we will also work problems that focus on the particulate representation and other concepts. We could be asked to draw a diagram that depicts what happens to the molecules when steam condenses into liquid water. EXAMPLE PROBLEM: Dry ice is solid carbon dioxide; it is called dry in large part because it goes directly from a solid to a gas without becoming a liquid under ordinary conditions. Draw a picture that shows what the carbon dioxide molecules might look like as a solid and as a gas. VISUALIZATION IN CHEMISTRY ▪Chemistry provides multiple simultaneous ways to view problems, including the completely abstract perspective of atoms and molecules that will never be observed directly. ▪We can explore this idea by thinking about refining of aluminum. ▪We can look at a large-scale industrial process while thinking in the microscopic perspective. Several steps in the processing of Bauxite Separating the aluminum oxides from the remainder of the rock. The first is digestion of the ore. Process engineers design digesters in which crushed ore, caustic soda and lime are mixed at the high temperature to create a slurry. We can visualize this process at the microscopic level: The molecular level pictures show aluminum as atoms of aluminum and oxygen, and the rock as silicon and oxygen (or silica).  The next step in aluminum refining is smelting. At this stage, a chemical reaction is induced where the aluminates, now dissolved in a material called cryolite (Na3AlF6 ), lose oxygen atoms to carbon rod, forming relatively pure aluminum and carbon dioxide. MATERIAL SELECTION AND BICYCLE FRAMES For the average rider who doesn’t wish to spend a great deal of money on a bike, the frame is likely to be some alloy of steel. Using other materials for the frame can improve certain aspects of performance but also increase the cost of the bicycle. Among the properties that an engineer must consider in choosing a material for a frame are strength, density (affects the weight of the frame), and stiffness. Stiffness is related to a property called the ELASTIC MODULUS of the material. Elastic modulus measures the amount of stretch or compression a material experiences when it is stressed.  A high modulus will stretch very little even when experiencing large force, and a bicycle frame composed from such a material would seem stiff. The strength of the material is formally measured by the property called the YIELD STRENGTH. The yield strength measures the amount of force required to produce a specified deformation of the material. A stronger material can withstand greater forces before it deforms and so has higher yield strength. There are benefits from having a lighter frame, materials with low densities are also desirable. Three most common metal for bicycle: Material Elastic Modulus (psi) Yield Strength Range(psi) Density (g/cm3) Aluminum 10.0 x 106 5.0 x 103 – 6.0 x 104 2.699 Steel 30.0 x 106 4.5 x 104 - 1.6 x 105 7.87 Titanium 16.0 x 106 4.0 x 104 - 1.2 x 105 4.507  Although aluminum is light weight, it is neither as strong nor as stiff as steel or titanium. Steel is the strongest, stiffest, and heaviest of the materials. The engineer has more than the choice of material available in making a design for a bicycle frame. The size and connectivity of the tubing can also be adjusted. Aluminum frames generally feature tubing with much larger diameter than that in steel or titanium frames. These larger diameter tubes give the frame itself stiffer feel. New aluminum alloys containing trace amounts of scandium can achieve lower frame weights without the large tubing diameters The extremely aerodynamics bikes preferred for high-speed time trial racing are most often made from carbon fiber composites that are molded easily into exotic shapes that reduce air resistance. “Chemistry is the science of matter, and since all engineering designs involve matter, therefore, there are links between chemistry and engineering.”