Chemistry: Methods and Measurement (Chapter 1) PDF

CHEMISTRY: METHODS AND Unit Conversion: English and Metric Systems MEASUREMENT (Chapter 1) conversion factor/ series of conversion factors- used in converting o...

CHEMISTRY: METHODS AND Unit Conversion: English and Metric Systems MEASUREMENT (Chapter 1) conversion factor/ series of conversion factors- used in converting one unit to another and relate Chemistry - study of matter. two units. Biochemistry- life at molecular level - factor label method Organic Chemistry - Carbon and hydrogen Inorganic Chemistry- all elements Conversion of units from one system to another Analytical Chemistry- analysis of matter Physical Chemistry - Behavior of matter A bridging conversion unit – used to convert a quantity expressed in units of one system to an The Methodology equivalent quantity in other system. Observation of a phenomenon The conversion may be represented as three step A question process: A Hypothesis 1. Conversion from the units given in the problem Experimentation (The scientific method) to a bridging unit. Theory - further experimentation New Hypothesis - Development of new 2. Conversion to the other system using the bridge. experimentation and hypothesis Law, Theory, Hypothesis and model 3. Conversion within the desired system to units required by the problem. Law - a statement of observed behavior for which no exceptions have been found. Summarizes the Error, Accuracy, Precision and Uncertainty similar behavior of all matter. Error – the difference between the true value and Theory - a hypothesis supported by testing our estimation, of the value. (experimentation) that explains scientific facts and can predict new facts. - Random error causes data from multiple measurements of the same quantity scattered in a Hypothesis - simply an educated guess; a more or less uniform way around some average reasonable attempt to explain an observation, or value. series of observations in a common-sense way. - Systematic error causes data to be either smaller Model - a system often used to make ideas more or larger than the accepted value. clear. Accuracy – the degree of agreement between the Science and Technology true value and the measured value. Technology - the conversion of a material or Uncertainty – the degree of doubt in a single information from its current form to a more useful measurement. form. Precision – a measure of the agreement of Applied Science - the use of scientific principles to replicate measurements. meet human needs. Significant Figures Science - breeds technology with both its benefits Significant figures is defined to be all digits in a and its potential dangers. number representing data or results that are known with certainty plus the first uncertain digit. Data, Results and Units Recognition of Significant Figures A scientific experiment produces data. Results are the outcome of an experiment. Rule: All nonzero digits are significant Units defines the basic quantity of mass, volume, 7.314 has four significant digits. time or whatever quantity is being measured.  Rule: The number of significant digits is the answer can be nor more precise than the least independent of the position of the decimal point. precise number from which the answer is derived. 73.14 has four significant digits. Rounding off numbers Rule: Zeros located between nonzero digits are significant. Rule: When the number to be dropped is less than 60.052 has five significant figures. 5, the preceding number is not changed. When the number to be dropped is 5 or larger, the preceding Rule: Zeros at the end of a number are number is increased by one unit. significant if the number contains a decimal point. Experimental Quantities 4.70 has three significant figures. The quantities that are most often determined Rule: Trailing zeros are insignificant if the include mass, length, volume, time pressure and number does not contain a decimal point and are energy. significant if a decimal point is indicated. 100 has one significant figure. Mass – describes the quantity of matter in an 100. has three significant figures object. Zeros to the left of the first nonzero integer are - Weight is the force of gravity on an object. not significant; they serve only to locate the position of the decimal point. - Weight = mass × acceleration due to gravity 0.0032 has two significant figures - Mass is a result of a comparison of an unknown Scientific Notation mass with a known mass called standard mass. Also referred as exponential notation which involves the representation of a number as a power - Balances are instruments used to measure the ten. mass of materials. Rule: To convert a number greater than 1 to Volume - You will often find the volume of an scientific notation, the original decimal point is object stated in terms of some unit of length. moved x places to the left, and the resulting number is multiplied by 10. The exponent is a positive For example, to calculate the volume of a box we number equal to the number of places the original might multiply the length by the width by the height. decimal point was moved. The SI unit of volume is the cubic metre, Rule: To convert a number less than 1 to scientific abbreviated m³. notation, the original decimal point is moved x places to the right, and the resulting number is For most practical purposes, therefore, we use the multiplied by 10−. The exponent (-x) is a negative metric unit of volume, the litre (L). For liquid number equal to the number of places the original measure in English System, the basic unit is the decimal point was moved. gallon, which may be divided into quarts, pints, or gills. Significant Figures in Calculation of Results Time - The standard unit of time is the second. ADDITION AND SUBTRACTION the answer cannot have greater significance than Matter may be characterized by measuring the any of the quantities that produced the answer. (2 time required for a certain process to occur. decimal). MULTIPLICATION AND DIVISION The rate of a chemical reaction is a measure of In multiplication and division, the decimal point change as a function of time. position is irrelevant. It is the number of significant figures that is important. Temperature - is the degree of “hotness” of an Accuracy and Precision object. Precision and accuracy are distinctly different The temperature of an object is the measure of concepts and should not be used interchangeably. the amount of heat in the object. (strictly not true) Precision refers to how closely individual measurements agree with each other. It is usually An object increases in temperature because its expressed in terms of percent deviation. heat content has increased and vice versa, however the relationship between the heat content and Absolute deviation (AD) is the difference between temperature depends on the composition of the the measured value (Mo) and the mean (M) for the material. set of several measurements. Three common temperature scales are Fahrenheit Absolute error is the actual difference between the (°F), Celsius (°C), and Kelvin (K). measured value and the accepted value. Although Fahrenheit temperature is most familiar Percent Error can also be obtained by the absolute to us, Celsius and Kelvin temperature are used difference between the accepted value (or true value) exclusively in scientific measurements. and the average measurement (or average experiment value) divide by the accepted value. It is often necessary to convert a temperature reading from one scale to another. LABORATORY LESSON 1: INTRODUCTION Energy - is the ability to do work. COMMON LABORATORY APPARATUS The first and foremost rule of any laboratory is to be Categorized as either kinetic energy – energy in safe! This may seem obvious, but people often motion or potential energy, the energy of position. disregard safety protocols for one reason or another, putting themselves and those around them in danger. The principal forms of energy are light, heat, The best thing you can do is to make sure you mechanical, electrical, nuclear and chemical energy. follow all safety protocols at all times. Heat energy may be represented in units of Safety Goggles and Safety Equipment calories or joules : 1 calorie (cal) = 4.18 joules (J) Safety goggles are required wear in all chemistry One calorie is defined as the amount of heat laboratories. energy required to change the temperature of 1 gram of water 1 °C. - Not wearing them puts you in danger of eye irritation and possibly blindness in the case of an Concentration - is a measure of the number of accident. particles of a substance, or the mass of those particles, that are contained in a specified volume. - A small droplet of acid could splash out of the container at any time. Better safe than permanently Concentration is a widely used way of blinded! representing relative quantities of different substances in a mixture of those substances. Latex gloves - should be used when there is a possibility of corrosive chemicals spilling onto your Density and Specific Gravity hands. The density of a substance is defined as the mass A laboratory apron or coat can also prevent of that substance per unit volume (often expressed injury in case of spills or splashes. in grams per cubic centimetre: g/cm3). Density depends on the temperature because the volume of A beaker is a common container in most a substance can change in temperature. Therefore, laboratories. when comparing densities of several substances, the measurements are all taken at a constant temperature. -It is used for mixing, stirring, and heating -When a large number of samples need to be tested chemicals. Most beakers have spouts on their rims and compared, test tubes are used to make this to aid in pouring. easier. -They also commonly have lips around their rims -They are also easily capped with a rubber or glass and markings to measure the volume they contain, stopper. although they are not a precise way to measure liquids. Beakers come in a wide range of sizes. A watch glass is just a round piece of glass that is slightly concave/convex (think of a lens). Erlenmeyer flasks also known as Conical flasks. - It can hold a small amount of liquid or solid. They can be used for evaporation purposes and also can Erlenmeyer flask was named after its inventor in function as a lid for a beaker. 1861. - It has a narrow neck and expands toward its base. A crucible is a small clay cup made of a material that can withstand extreme temperatures. They are -This allows easy mixing and swirling of the flask used for heating substances and come with lids. without too much risk of spilling. A laboratory funnel is just like any other funnel -The narrow opening also allows for the use of a except that it was designed to be used in a rubber or glass stopper. laboratory setting. They can be made of plastic or glass and can have either a short stem or a long -It can easily be clamped to a ring stand (discussed stem, depending on what they are needed for. There below) as well as heated or shaken mechanically. are several sizes that can be chosen from based on the amount of liquid that needs to go through them An important safety tip here is to never heat this quickly. flask while it is capped. This could cause a pressure build-up that could result in explosion. This is a primary measuring tool for the volume of a liquid. There are several markings up and down Florence flasks also known as Boiling flasks. the length of the container with specific increments. Graduated cylinders come in many sizes. The Florence flask has a round bottom and a long neck. smaller they are in diameter, the more specific the -It is used to hold liquids and can be easily swirled volume measurements will be. and heated. A volumetric flask is a round flask with a long -It can also easily be capped by rubber or glass neck and flat bottom. stoppers. -It is used to measure an exact volume of liquid. -Once again, safety dictates that this flask never be There is a small line on the neck that indicates how heated when capped. Pressure build-up and far to fill the bottle (use the bottom of the meniscus). explosions can and do occur. -They come with special caps that will not let Test tubes being lifted with tongs from a rack. anything in or out. A test tube is a glass tube with one end open and Droppers These are small glass tubes with narrow the other end closed. tips on one end and a rubber bulb on the other. They suck up liquid that can then be squeezed out -The closed end is rounded. Test tubes are used to in small drops. These can be used to add an hold small samples. indicator to a solution about to be titrated. -They are primarily used for qualitative assessment There are a large variety of pipettes designed to and comparison. accomplish specific goals. However, they are all for measuring an exact volume of liquid and placing it - A common place to see these is the biochemistry into another container. laboratory. A buret. These are usually attached with a clamp to COMMON LABORAOTY OPERATIONS AND a ring stand. TECHNIQUES -buret is a glass tube that is open at the top and Using a Thermometer comes to a narrow pointed opening at the bottom. 1. Make sure that your thermometer covers the right -A buret is used for extremely accurate addition of temperature range. liquid. 2. The bulb must not touch the container and must be at the center of the substance. The ring stand is used to suspend burets, beakers, 3. Never use a thermometer to stir a liquid. Use a flasks, crucibles, etc. above other containers or, in stirring rod. some cases, a heat source (such as a Bunsen burner, 4. Read the temperature to the nearest ½ degree, discussed below).Always make sure everything is after the height of the mercury or alcohol remains clamped to the stand tightly. steady. 5. When reading the temperature, make sure your Two tongs above and a pair of forceps below eye is level with the height of the liquid in the thermometer. Tongs and forceps are for grabbing things that should not be touched by hand. Using a Balance - Some tongs are specially made to hold beakers, 1. Place your container gently on the center of the others to hold test tubes, and so on. There are also pan. general tongs. 2. Press the tare button, make sure that it is now measuring zero. - Forceps are used to grab small things like solid 3. Add your substance, making sure it is not hot chemicals that are broken into chunks, so they can (Air currents produced will influence your be safely handled and added to containers. readings). 4. If you spill anything on the balance or bench Spatulas and scoopulas are for scooping solid clean it immediately. chemicals. They are typically used to scoop a 5. Record your readings. chemical out of its original container onto a weigh 6. If you are measuring several substances, always boat so that it can be weighed on a balance. use the same balance to eliminate any error between balances. A laboratory thermometer is used for measuring the temperature of liquids. It can be made of glass Using a Measuring Cylinder or it can be a thermocouple made of different metals. 1. Always take the reading from the bottom of the meniscus. A Bunsen burner is a mechanical apparatus that is 2. Only take the reading when you are at eye level. connected to a flammable gas source. 3. Take the reading to the nearest centimeter cubed (cm3 /ml) if possible. - There is a knob to adjust the amount of gas flow and a rotating collar that controls airflow. - These both must be adjusted to get an ideal flame Transferring a Solid for heating purposes. The burner is lit with a striker. 1. Always use a spatula. 2. Never dig the spatula deep into the substance. A balance is used to weigh chemicals. The 3. Never over fill the spatula. chemicals are always in some form of container and 4. Don’t sprinkle a solid into the top of a test tube; never placed directly on the balance. it may stick to the sides. Instead, tip the solid off when the spatula is as deep into the test tube as you - It is important not to move a balance because they can get. have been calibrated for the exact position they are in. Pouring Liquids from a Reagent Bottle Heating Materials in a Test Tube 1. Hold the bottle with the label pointing towards 1. Always use a suitable test tube holder and grip your palm to stop any drips from damaging the the top of the test tube. label. 2. Always point the mouth of the test tube away 2. Pour the liquid along a stirring rod. from you and others. 3. Move the tube over the hottest part of the flame. Using Filter Paper Do not leave it stationary. 4. Liquids are poor conductors; always shake the 1. Fold the round filter in half. tube when you are heating a liquid. 2. Fold the filter in half again. 3. Open the cone and tear the outside corner off. Evaporating a Liquid 4. Place the cone in the funnel and add some water or any other solvent you may be using to help it 1. Place the liquid in an evaporating dish and place remain in place. that over a beaker of boiling water. 5. Pour the liquid that you are filtering down a 2. Continue heating until solids remains the stirring rod to eliminate any drips. evaporating dish. Smelling a Chemical Burning Substances 1. Fill your lungs with air before smelling the gas 2. Dilute the gas with air by wafting it towards your 1. A combustion spoon is used to burn solids or nose. liquids in a chosen gas. Using a Litmus Paper 1. Dip a stirring rod into the liquid that you want to test. 2. Touch the stirring rod to the litmus paper that is lying flat on a watch glass. This will stop you from contaminating your sample. Mixing the Contents of a Test Tube 1. Tap the tube to vibrate the contents. Using Mortar and Pestle 1. Place the material into the mortar. 2. Grind to pulverize and pound to reduce the size of the particles. Lighting a Bunsen Burner 1. Attach the burner to the gas. 2. Make sure the air intake valve is closed. 3. Turn on the gas main and gas valve on the burner. 4. Quickly strike the match or lighter and ignite the gas. 4. Adjust the height of the flame with the gas valve at the burner’s base or the main valve. 5. Adjust the air intake to obtain a blue cone.  HIGHLIGHTED TOPICS - before any measurememt made, there is aready same measurement MORE. Vernier Caliper - an instrument that measures the - solution? ADD this error reading. internal diameter as well as the external diameter and distances of the object. - this device takes more precise meausrements than the regular ruler. Procedures on how to use vernier caliper 1. Loosen the lock screw and use the thumbscrew to check if the zero mark of the vernier scale coincides exactly with the zero mark of the main scale. 2. Place the object between two jaws to measure the inside diameter or outside diameter or distances. In the measuring jaw and move the thumb grip to position the object. 3. Read the measured value. Micrometer Caliper - a micrometer screw gauge is a small measuring device that works on the screw principle and is used for measuring dimensions smaller than those measured by the vernier caliper. Procedures on how to use micrometer screw gauge: 1. As in using a vernier caliper, make sure that the zero of the micrometer caliper coincides exactly with the zero of the main scales. 2. Place the object between the anvil and the spindel and move the rachet screw to position the object. 3. Measure the dimensions or diameter of the objects asked for the experiment. Zero Errors in Vernier Calipers for the reading to be accurate, there should be no zero. the two zero marks on the main scale and the vernier scale must for a straight line, when the jaws are complete closed. Correcting Zero Error Positive zero error - mark of the varnier scale is slightly to the right of the main scale. - before any measurements MORE. - solution? SUBTRACT this error from reading. Negative zero error - the zero mark of the vernier scale is slightly to the left of the main scale