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Chemistry Lab Manual
 

Chemistry Lab Manual

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    Chemistry Lab Manual Chemistry Lab Manual Document Transcript

    • Chemistry Lab ManualName:_____________Introduction to working as a Chemist.Use a highlighter as you work through this booklet. ESL students, make vocab lists of theterminology that is defined or described here.Assessment Statements Outline the Scientific Method  State SI units of measurement for Identify independent, dependent & controlled  Mass: grams (g) variables.  Length: Metres (m), millimeters (mm) Demonstrate correct and safe use of laboratory  Concentration: molarity (M) o equipment.  Temperature: Degrees Celsius ( C) Distinguish between quantitative and qualitative  Volume: Litres (L) or millitres (mL) data  Density: grams per cubic centimeter 3  Qualitative is descriptive, not using (g/cm ) numbers, e.g. properties, colour, gas  Conductivity: Siemens (S) production, sound, odor.  Acidity or alkalinity (pH)  Quantitative is mathematical, including  Energy: Joules (J or kJ)Determine the  Raw data (as recorded ) uncertainty of digital and analog measuring tools  Processed (after calculations)  Usually ± 1 of the smallest division Distinguish between accuracy and precision  Calculate the % error of a given or recorded set  Accuracy describes the correctness of a of values set of measurements  ((Measured – True) / True) x 100  Precision describes the repeatability of a  State values to appropriate numbers of set of measurements significant figures  Calculate values to appropriate numbers of significant figuresRelated Concepts:  01.1 Element symbols (Quia quiz: http://www.quia.com/quiz/3246640.html)  01.2 Accuracy, Precision, Error, Uncertainty (Quia quiz: http://www.quia.com/quiz/3507626.html)  01.3 SigDigs and Notation (Quia quiz: http://www.quia.com/quiz/3504378.html)Command Terms: Be sure you understand what is being asked of youAnalyse Break down to identify key parts. Interpret information to reach conclusions.Apply Use knowledge & understanding in response to a real situation or given circumstances.Calculate Obtain a numerical answer, showing relevant stages in the working.Define Give the precise meaning of a word, phrase, concept or physical quantity.Describe Give a detailed account or picture of an event, pattern, process or pattern.Design Produce a plan, simulation or model.Determine Obtain the only possible answer.Discuss Offer a considered and balanced review that includes a range of arguments, factors or hypotheses. Opinions or conclusions should be presented clearly and supported by appropriate evidence.Distinguish Make clear the differences between two or more concepts or items.Evaluate Assess the implications and limitations; make judgments about the ideas, works, solutions or ideas in relation to selected criteria.Explain Give a detailed account including reasons or causes.Identify Provide an answers from a number of possibilities. Recognise and state briefly a distinguishing fact or feature.Label Add title, labels or brief explanation(s) to a diagram or graph.List Give a sequence of answers with no explanation.Outline Give a brief account.Recall Remember or recognize from prior learning experiences.State Give a specific name, value or other brief answer without explanation or calculation.Suggest Propose a solution, hypothesis or other possible answer. 1
    • Use Apply knowledge or rules to put theory into practice. 2
    • AssessmentSubmit for checking once complete. Ask for help when needed.Criterion F: Attitudes in Science(Highlight the statements that best fit your effort)Level Level descriptor 0 The student does not reach a standard described by any of the descriptors below. 1–2 The student requires some guidance to work safely and some assistance when using material and equipment. The student requires some guidance to work responsibly with regards to the living and non-living environment. When working as part of a group, the student needs frequent reminders to cooperate with others. 3–4 The student requires little guidance to work safely and little assistance when using material and equipment. The student works responsibly with regards to the living and non-living environment. When working as part of a group the student cooperates with others on most occasions. 5–6 The student requires no guidance to work safely and uses material and equipment competently. The student works responsibly with regards to the living and non-living environment. When working as part of a group, the student cooperates with others.Expectations:  Your working area and personal space are kept clean and neat at all times.  You work safely with regard to chemicals, equipment and others.  You are sensible and precise in your use of science equipment and materials.  All equipment is properly cleaned and returned to the proper place.  You show cooperation and respect for others in your group work.Comments:Criterion E: Processing Data (Formative) (Highlight the statements that best fit your effort)Level Level descriptor 0 The student does not reach a standard described by any of the descriptors below. 1–2 The student collects some data and attempts to record it in a suitable format. The student organizes and presents data using simple numerical or visual forms. The student attempts to identify a trend, pattern or relationship in the data. The student attempts to draw a conclusion but this is not consistent with the interpretation of the data. 3–4 The student collects sufficient relevant data and records it in a suitable format. The student organizes, transforms and presents data in numerical and/or visual forms, with a few errors or omissions. The student states a trend, pattern or relationship shown in the data. The student draws a conclusion consistent with the interpretation of the data. 5–6 The student collects sufficient relevant data and records it in a suitable format. The student organizes, transforms and presents data in numerical and/or visual forms logically and correctly. The student describes a trend, pattern or relationship in the data and comments on the reliability of the data. The student draws a clear conclusion based on the correct interpretation of the data and explains it using scientific reasoning.Comments: 3
    • The Scientific MethodScience is never about proving something right or wrong. It is about making observations, forminghypotheses and developing methods to test those hypotheses. If the data support our hypothesis,we can try to explain why. If not, we develop a new hypothesis and a new method to test that.Use the correct language!A FACT is something that is observable and true. It is a fact that the Sun shines. It is a fact that reacting HCl and Mg produces a gas.A LAW is something that always happens in defined conditions, following “if.. then…” rules. The Law of Conservation of Mass states that atoms (matter) can neither be created nor destroyed. If a reaction occurs, then all the atoms involved as reactants must be accounted for in the products. The Law of Diffusion states that molecules in fluids (liquid, solution or gas) will diffuse from areas of high concentration to areas of low concentration. If the concentration gradient is high, the rate of diffusion will be faster.A HYPOTHESIS is a scientific prediction that is testable and can be explained with a reason. A NULL Hypothesis is the standard against which we compare the outcome.  “There is no significant difference/ effect of... on…” The ALTERNATE Hypothesis is your prediction:  It makes clear the independent and dependent variables  Independent Variable (IV): The variable that is being changed - Usually requires at least five increments (different values) - Usually plotted as the x-axis on a graph  Dependent Variable (DV): The variable that is being measure in response to the IV - Usually plotted as the y-axis on a graph It predicts how incremental changes in the independent variable could affect the magnitude of the dependent variable. It can be testable under Controlled Conditions  Controlled Variables: all the factors that might impact the outcome of the investigation must be kept at the same value to ensure the results are reliable.HYPOTHESIS TESTING Good scientists design reliable experiments to test the validity of the hypothesis  RELIABILITY:  Is the method easily repeated? Is it free of random and systematic error?  Are the results reliable? This is indicated by the variability of the data.  VALIDITY:  To what extent does the method allow the RQ to be addressed?  To what extent is do the results support the hypothesis?A THEORY is the highest level of certainty in science. It is supported by lots of empirical evidence.It has been tested over and over again and can be explained scientifically. It has not beendisproven… yet. Atomic theory states that all matter is composed of atoms, made up of a nucleus containing protons and neutrons, outside which is a cloud of electrons. Kinetic theory of gases state that particles (atoms and molecules) in gases are moving randomly, colliding with each other. They move more rapidly at high temperature. Cell theory states that all living things are made of cells; cells are the smallest units of life; cells come only from other cells. 4
    • What is/areDATA?“Not everything that can be counted counts. Not everything that counts can becounted.” Albert Einstein.QUANTITATIVE DATA (EMPIRICAL DATA) Can be measured and compared using numbers Can be continuous or non-continuous.  Continuous: on a scale, such as time, temperature, concentration  Non-continuous: not scaled, such as categories, groups. Includes the values of the increments of the IV Includes raw and processed data of the DV  Raw data includes all numbers recorded during the experiment.  Processing shows how transformations work with the data: calculations  Processed data are the the final results, after calculations  Presented data are the tables and graphs that are producedQUALITATIVE DATA (OBSERVATIONAL DATA) Descriptive, not numerical Provides important insights that might help explanationsBoth types of data are essential in lab reports. ……….o0O0o………..There’s no such word as ‘amount’!What do you really mean when you say “amount”?Matter is anything that has mass and volume(takes up space): We measure mass in kilograms (kg), or grams (g). We measure volume in litres (L) or millilitres (mL) (sometimes cm3).We also describe other quantities: Time in seconds (s) Length or distance in metres (m) Energy in joules (J) or kilojoules (kJ) Heat/temperature in degrees Celcius (oC) (the SI* unit is Kelvin, K) Quantity of a substance in moles (mol) Concentration of a solution in moles per litre (M) Acidity or alkalinity in pH (0 is a strong acid, 7 is neutral, 14 a strong base) Electrical conductivity of a solutionin Siemens (S)*Standard International (SI)units are based on the metric system – numbers that divide easilyinto tens and hundreds. Most countries in the world use these units and it makes calculationsmore straightforward.In this activity, we’ll learn how to measure some of these physical quantities using the appropriatetools in the lab. Complete this lab manual as you go along – you will use it as a tool throughout thecourse. 5
    • Safety FirstWe must be safe in the lab at all times. Check that you can find these:  Goggles What should you do if there is an accident in the lab?  Fire blanket   Fire extinguisher  Phone Do not try to clean up broken glass – MrT will do it.Safe Bunsen ‘driving license’  How do you turn on the Bunsen? …………………………………………………………………………………………………… ……………………………………………………………………………………………………  What is the ‘safety flame’? ………………………………………………………………………………………………… …………………………………………………………………………………………………  What is the ‘roaring flame’ and which part is the hottest? ………………………………………………………………………………………………… ………………………………………………………………………………………………… NEVER point a hot container towards yourself or others. ALWAYS be careful in the Chemistry Lab!Visual guide to Chemistry Lab equipmentAs you work through the tasks, draw some simple diagrams of the lab equipment to help youremember the names.Beaker Conical flask Test tubeTripod & Gauze mat Test tube tongs Wash bottlePasteur (dropping) pipette Filter funnel Spatula 6
    • Units and Uncertainty (Quia quiz: http://www.quia.com/quiz/3507626.html)All measurements have uncertainties – a range of values in which the true measurement could lie.More precise measuring tools have a smaller degree of uncertainty.Significant Digits (or Significant Figures) Tutorial:http://is.gd/sigfigsWe use significant digits to communicate how precise a measurement is – how certain we are inour measurement. In the example above, there are 4 significant digits.Significant digits are: All non-zero digits (and all the zeroes in-between non-zeroes!) Any digits after a decimal pointBut they are NOT: Leading zeroes, e.g. 0.000345 has only 3 sigdigs: 345 Trailing zeroes with no decimal, e.g. 10,000 has only 1 sigdig (we can’t tell if it is exactly 10,000 or a number that is close and has been rounded).How many significant digits in these numbers? Write these numbers to 3 sigdigs:  123.45 _________ sig digits  12420 = _______________  123000 _________ sig digits  1.008 _________ sig digits  0.03209 = _______________  01.67 _________ sig digits  4050.0 = _______________  1000 _________ sig digits  1000.0 _________ sig digits  0.0101010 = ______________Calculating Significant DigitsWe can only report values to the minimum degree of certainty, so: When adding or subtracting, use the number of decimal places of the weakest value. When multiplying or dividing, use the number of sigdigs of the weakest value.1. 2.01 - 1.0 = 5. 3.44–4.0 =2. 123 + 456.789 = 6. 1.23 + 45.6 =3. 1.2 x 3.45 = 7. 0.66 x 1.34 =4. 34.678 /3.33 = 8. 1.34 / 0.66 = 7
    • Accuracy, Precision & Errors (Quia quiz: http://www.quia.com/quiz/3507626.html)There is always an element of error in our measurements.The accuracy of a measurement is how close it lies to the true value (“correctanswer”). The precision of a measurement is how repeatable that measurement is.Identify which of the dartboards shows (Circle): 1. High precision and high accuracy? Top - Middle - Bottom 2. Low precision and low accuracy? Top - Middle - Bottom 3. High precision but low accuracy? Top - Middle - BottomSystematic error is an error that is the same for all measurements and can beadjusted. For example, a digital balance that is poorly calibrated might measure0.5g too much each time.Random error is not consistent between measurements and cannot be adjusted.For example, errors introduced by using different recording tools or people.Identify which of the dartboards shows: 4. Random error: Top - Middle – Bottom 5. Systematic error: Top - Middle - Bottom Dartboard diagrams from http://preparatorychemistry.com/Bishop_Book_1_eBook.pdfScientific Notation (Quia quiz: http://www.quia.com/quiz/3504378.html)Often we produce measurements or readings with a large number of zeroes.We use scientific notation to present these numbers in a clear, standard format.Simple rules:  There is alwaysone digit before the decimal  It always ends x 10x(“times ten to the power of x”)  Significant digits are important. The examples below have 3sigdigs (1.23)  The value of x tells us how many places the decimal has been moved.  If you are making a large number small, x is positive.  If you are making a small number (less than zero) larger, X is negative.e.g. 1230000000000 can be written as 1.23 x 1012 The decimal has moved 12 places to the left.e.g. 0.000000000123 can be written as 1.23 x 10-10 The decimal has moved 10 places to the right.Expand the following notations:1.0 X 103= ______________________ 4.56 X 105= _____________________________1.0 X 10-6= ______________________ 7.01 X 10-4= _____________________________ 8
    • Statethe following in scientific notation to 3 significant digits: • 12340000 = _____________________________ • 00012340 = _____________________________ • 10101010 = _____________________________Compare the following measurements:3.04 x 104 kJ 3.040 x 104 kJ 3.0400 x 104 kJWhat is a Solution?A solution is a homogenous* mixture of a substance in a liquid. The solvent is the liquid, e.g. water or alcohol, which dissolves the… Solute, which is the solid, e.g. salt or sugar.  Label the solventand the solute in the beaker to the right. ----------->*mixtures can be: Homogenous = evenly distributed, like solutions Heterogeneous = unevenly distributed, like soup, oceans, mixtures of solids.Beaker from: http://www.wpclipart.com/science/beaker/beaker.png.htmlConcentration of a SolutionA more concentrated solution contains more molecules per unit volume.We measure the concentration of a solution by the number of moles of solute it contains per litre.This is called molarity, and uses the unit ‘M’. A 1M solution contains 1mole of solute per litre.One ‘mole’ of a substance is 6.02 x 1023 units (atoms or molecules). So a 1M solution of sugar has 6.02 x 1023 molecules of sugar per litre.Expand the notation above. 9
    • Measuring VolumeWe use graduated cylinders to measure volumes of a liquid. We do not use beakers or conicalflasks – the marks on those are estimates only.Label the meniscus on the diagram to the right. This is where we measure fluids. Put the cylinder on the table and move your eyes to read it.Observe these different-sized measuring cylinders. Complete the table. Size Markings every… Recorded volume (ml) Uncertainty (± ) 10mL 50mL 100mLIdentify which cylinder has: 1. The most precise gradations (markings): _______ mL 2. The biggest uncertainty: _______ mLAdd up the total volume of water in the four cylinders. Present your working and give the answerto the most appropriate significant digits. Explain your answer.…………………………………………………………………………………………………………………………………………..…………………………………………………………………………………………………………………………………………..…………………………………………………………………………………………………………………………………………..…………………………………………………………………………………………………………………………………………..Measuring MassWe use digital balances to measure the mass of a substance.  Check the range of the balance – do not press on it or add a mass that is heavier than the maximum. You will break it.  Use a measuring tray or paper on top of the stage. “Tare” (“zero”) it if you need to.  Never stack balances, push hard on the tray or drop them.  Never get the balance wet or dirty.Choose one known mass and measure it using three different balances. Complete the table.Balance Range (g) Recorded mass (g) Uncertainty (± ) What is this balance good for? A B C 10
    • Measuring TemperatureCompare the glass thermometer with the temperature probe on the data logger.Remember: Thermometers and dataloggers are NOT for stirring!  Measure the temperature of the solution/ liquid – NOT the container  Don’t touch the thermometer or probe against the glass  Wait for the temperature to stabilize before taking the reading Which would you choose to get Glass thermometer oC (± ) quick readings of a reaction that changes temperature? Temperature probe oC (± )Measuring pHWe use pH probes on the datalogger to measure the acidity oralkalinity of a solution. Strong acids have low pH, neutral pH is 7 andstrong bases have high pH.Measuring ConductivityIn some solutions, ions form. These are positive ions (cations +) ornegative ions (anions -). When these ions move, they carry electricalcharge, which can be detected with the conductivity probe. A highconcentration of ions will give a high conductivity. pH scale from:http://www.ec.gc.ca/acidrain/kids.htmlTake care of the probes:  Make sure the electrolyte bottle is secure when not being used.  Rinse gently with distilled water between every reading.  Do not stir or shake the probe.Taking readings:  Submerge the probe and wait for the reading to stabilize  Record the pH to an appropriate level of precisionRecord the pHand conductivityof these three solutions: Solution A B C pH (± ) conductivity μS (± ) This symbol means ‘micro’ or one-thousandth. 1 μS = 0.001 S (Siemens is the unit of conductivity)Probes must be calibrated regularly to make sure they are accurate (to avoid systematic error). 11
    • Matter, Elements & The Periodic Table Draw a helium atom:Matter is anything that has mass and volume (takesup space).All matter is made of atoms, which contain: Protons & neutrons in a central ‘nucleus’ A cloud of electronsThe number of protons is the atomic number and defines the element.An element is a substance that is made up only of atoms that contain the same number ofelectrons.The periodic table arranges elements based on atomic number, as well as into groups with similarchemical and atomic properties.It is very helpful to know the names of the most common elements, so that you can recognize them fromformulas and use them more quickly in your work. We will remember these elements, and complete somequizzes to help us do so. Try this quiz, which changes each time: http://www.quia.com/quiz/3246640.htmlSome rules: The first letter of the element symbol is always CAPITALISED, but any other letters must be lower-case Only capitalize the first letter of the name when it starts a sentence. Do not use capitals otherwise. e.g. the first element is hydrogenSymbol Name Symbol Name Symbol Name H hydrogen Cl Sn He helium Ar I Li lithium K Xe Be beryllium Ca Cs B boron Cr Ba C carbon Mn Pt N nitrogen Fe Au O oxygen Co Hg F fluorine Ni Pb Ne neon Cu At Na sodium Zn Rn radon Mg magnesium Br Fr francium Al aluminium Kr Ra radium Si silicon Rb U uranium P phosphorous Sr Pu plutonium S sulphur AgCompounds are formed when two or more elements are combined chemically.Mixtures are made up of two or more substances that are not combined chemically. Eachsubstance keeps its own properties. Mixtures can be separated: Filtration separates differently-sized solid particles, or solids from liquids/ solutions. Evaporation separates a solute from a solvent in a solution. Distillation (evaporation and condensation) separates liquids based on their boiling point. 12
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