Experimental Techniques & Data Handling Notes

Experimental Techniques

Safety

• Being Principled: Acting with integrity, honesty, fairness, and taking responsibility for actions in experimental work.

• Accident Prevention:

  • Lab safety is crucial; includes wearing PPE, risk assessments, and safer alternatives.

  • Safety considerations: Protect experimenter, environment, and others in the lab

• Personal Protective Equipment (PPE):

  • Commonplace: Safety goggles and lab coats.

  • Historical Perspective: Note that PPE use wasn't always standard; analyze old photos for safety risks.

• Risk Assessment:

  • Completed before experiments, involving:

    • Hazards: Substances/activities causing harm (e.g., hot crucible).

    • Risks: Evaluating harm severity/likelihood (e.g., burns from touching a hot crucible).

    • Control Measures: Minimizing risk/removing hazards (e.g., cooling crucibles, using tongs, balance location).

• Disposal Procedures:

  • Following local rules/policies to protect the environment and disposal personnel.

  • Reagent Recovery: Left-over reagents should be recovered for future use if possible.

• Green Chemistry Principles: Accident prevention and waste prevention.

Academic Integrity

• Respecting Others' Ideas: Citing information sources to give credit.

• Distinguishing Own Words: Using quotation marks and citations for others' ideas.

• Paraphrasing: In-text citations are needed when rephrasing someone else's ideas.

• Full References:

  • Included at the end in a bibliography/works cited/references section.

  • Minimum information: author name, publication date, source title, page numbers, URL (if applicable).

• Referencing Style: No specific style mandated by IB, but consistency is expected.

Measuring Variables

• Handling Data: A vital skill.

• Qualitative Data: Non-numerical information (e.g., color changes, bubbling).

• Quantitative Data: Numerical information from measurements.

• Measurement: Core aspect of science, providing quantitative data.

Accuracy and Precision

• Precision:

  • Repeating measurements assesses precision.

  • Precise values are close to each other (small range).

• Accuracy: How close a measured value is to the true value.

• Measurements Assessment: Assessed in terms of validity and reliability.

Figure 5: illustrates values close to each other and the true value.

Figure 6 demonstrates the difference between accuracy and precision.

Validity and Reliability

• Validity: Measuring what it's meant to measure;

  • Invalid Measurement Example: pH with an improperly calibrated probe.

• Reliability: Consistent results upon repetition.

  • Assessed with repeatability: agreement of results when using the same methods by the same experimenter.

• Good Practice: Repeating trials to calculate a mean, assess precision and spot outliers.

• Number of Trials: Three trials are generally a good rule of thumb.

• Concordance: For titrations, measurement should be repeated until several concordant values are obtained; values agree with each other and is generally a range of less than 0.1 cm^3 (although this value is not set in stone, and it is best to specify it when writing up lab investigations).

• Reproducibility: Consistency of results by different people, instruments, and reagent sources.

• Reporting Findings: Include detailed experimental methods to allow reproduction by others.

Types of Measurements

• Key types in chemistry: mass, volume, time, temperature, length, pH, electric current, and electric potential difference.

Mass

• Balance Precision: Greater precision balances measure to more decimal places.

• Trailing Zeroes: Don't omit trailing zeroes; they indicate precision.

• Gravimetric Analyses: Measuring mass changes during reactions (e.g., gas production or absorption).

• Container Mass: Record the mass of the empty container in gravimetric analysis.

Volume

• Equipment Suitability: Depends on function and desired precision.

• Measuring Cylinders: Not very precise; used for approximate volume.

• Volumetric Analyses: Need pipettes, burettes, and/or volumetric flasks.

• Beakers/Conical Flasks: For holding, not precise measurement.

• Meniscus: Read from the bottom of the meniscus for aqueous solutions (Figure 10); mercury forms an upside-down meniscus (Figure 11).

Time

• SI Unit: Second (s).

• Rate of Reaction: Stopwatch to record time for gas production.

• Uncertainty: Context-dependent; experimenter reaction time often more significant than stopwatch precision.

Temperature

• Measurement: Use digital or analogue thermometers.

• Accuracy/Precision: Depends on the experiment's context.

• Continuous Monitoring: Temperature probes connected to data loggers (Figure 14).

Length

• Measurement: Rulers or calipers.

• Scale Resolution: Impacts significant figures; estimate the last digit (Figure 15).

pH

• Estimation: Indicators like universal indicator/red cabbage extract; compare color to a key.

• Reliable Measurement: Properly calibrated pH probe (Figure 18).

Electric Current

• Measurement: Amperes (A), using an ammeter.

• Circuit Connection: Ammeter in series; current is the same throughout the series circuit.

• Conductive Liquid/Solution (Electrolytes): Requires inert electrodes (graphite/platinum).

• Electrical conductivity: Is the ability to conduct charge and can be measured directly with a probe.

• Influencing Factors: Electrode surface area, distance, voltage, and materials affect resistance.

• Reaction Monitoring: Conductivity measures progress when ions are consumed/produced; conductivity depends on ion concentration/identity.

Electric Potential Difference

• Measurement: Volts (V) using a voltmeter.

• Circuit Connection: Voltmeter in parallel to the component being measured.

• Voltaic Cells: Potential difference between anode/cathode = cell potential (Figure 22).

• Electromotive Force (emf): Maximum potential difference when no current flows; measured with high-resistance voltmeters.

Applying Experimental Techniques

Preparation

• Standard Solution Preparation:

  1. Weigh solid/liquid solute using an analytical balance.

  2. Dissolve in a small volume of deionized water; stir with a glass rod.

  3. Transfer to volumetric flask using a funnel.

  4. Rinse beaker, rod, and funnel 3x with deionized water, adding to the flask.

  5. Add deionized water to the graduation mark.

  6. Stopper and invert at least ten times to mix.

  7. Transfer to labeled reagent bottle (formula, concentration, date, initials, hazards).

Figure 24: Demonstrates the preparation of a standard solution.

• Inappropriate Equipment: Don't use measuring cylinders/beakers for volume measurement; balance must have at least four significant figures.

• Preparation of solutions by dilution: Use a burette or volumetric pipette and transfer to a volumetric flask and add deionized water up to the graduation mark.

  • Concentrated \times Volume = Concentrated \times Volume, which is expressed as: c1 \times V1 = c2 \times V2

  • Serial dilutions are used to accurately prepare a series of solutions of increasingly lower concentration.

Figure 25 outlines performance preparation of a simple solution.
Figure 26 demonstrates a serial dilution.

Reflux and Distillation

• Similar equipment, different purposes.

• Reflux: Heating reaction mixtures minimizing loss of volatile substances.

• Distillation: A separation method separating of components of a mixture to their boiling points.

• Condenser Used in Both: Tube-within-a-tube cooled by continuous water flow.

• Anti-bumping granules: Ensuring smooth boiling.

Figure 27: a) Represents Reflux Apparatus while b) Represents simple distillation apparatus.

• Simple Distillation: Separates volatile liquid from non-volatile solid or liquids with very different boiling points.

• Fractional Distillation: Separates miscible/volatile liquids with similar boiling points.

• Fractionating Column Fitting: Allows repeated cycles of vaporization/condensation.

Figure 28 Represents fractional distillation apparatus.
Figure 29 Represents industrial fractional distillation.

Isolation

• Drying to a Constant Mass: Solid samples might contain water, samples are often dried to a constant mass to ensure that they do contain any water(or other volatile impurities).

  1. heat the sample

  2. allowing it to cool for a few minutes

  3. weighing it

  4. repeating the process until two consecutive equal masses are obtained.

  • Heating is done with Bunsen burners, hotplates, and drying ovens and carefully so it doesn't decompose the solid.

• Separation of mixtures: Depends on the properties of the mixture of components.

• Filtration: Separates particles by size through a medium with holes/pores.

  • Insoluble solids from liquids.

  • Residue- the Solid left behind in filter paper .

  • Filtrate: the liquid that passes through the filter.

• Gravity filtration is the filtrates passes due to gravity.

Figure 30: Describes gravity filtration.
Figure 31 shows the steps for making a fluted cone from circular filter paper.

• Vacuum filtration: Quicker.

  • Lay Sheet of moist filter paper flat on the perforated plate inside a Buchner funnel.

  • Suction from a vacuum pump draws the liquid through the filter paper and into a receiving flask underneath

• Crystallization. solid can be crystallized out of a solution by removing the solvent.

  • Most of the solvent is evaporated off by heating it over boiling water until the solution becomes saturated.

  • Spotted a drop of it onto a cold tile and watching for the formation of crystals as it cools.

  • Finally, any remaining solvent is removed from the crystals by filtration and are allowed to dry to constant mass on a wrist glass.
    *
    Figure 32 Shows the Vacuum Filtration Apparatus.
    Figure 33: Shows the Crystallization Apparatus.

• Miscible Liquids : Can be separated by fractional distillation.

• Immiscible Liquids:

  • Oil and Water which are placed in a separating funnel (Figure 35).

  • After ensuring that the stopcock is closed, the mixture is poured into the funnel; Soon after, the liquids form two distinct layers.

  • Denser, lower layer is then drained into an underlying beaker by opening the stopcock.

• Separating funnels: Are also used to selectively extract solutes from one solvent into another.

Recrystallization

• Purification process based on selective solubility used to isolate a desired solid from mixture of solids.

• Isolated technique requires a solvent to selectively dissolved different components of the mixture depending on the temperature.

  • Insoluble impurities that are insoluble in the solvent at all temperatures

  • Impurities that are soluble in the solvent at all temperatures

  • The desired solid that can only be dissolved at hot than insoluble when cold

Figure 36 Demonstrated Recrystallization Process.

Analysis

Melting Point Determination:

• Purity of a solid sample is placed inside a capillary tube.

• The sample is heated, observed closely, noting down the temperature(s) at which begins and finishes melting.

• Pure substances have sharp melting points that agree with published values.

• If impurities are present, the melting point is usually lowered and the solid melts over a temperature range.

Figure 37 Shows Melting Point Determination with a Thiele tube.

Chromatography

• Collective term for methods analyzing a mixture by separating components by phase affinities.

• Two main types:

  • Paper Chromatography.

  • Thin-Layer Chromatography (TLC).

Figure 38: Shows the set-up for paper chromatography, and the resulting chromatogram.
Figure 39: Shows Thin-layer chromatography (TLC).

Calorimetry

• Technique to measure heat released/absorbed during a chemical reaction.

• Enthalpy change causes a measurable temperature change in known mass of water.

Figure 42: Calorimetry of the reaction between magnesium and dilute hydrochloric acid.

Heat loss is minimized by setting up an insulated container. (See Figure 42).
Enthalpies of combustion can be determined using the apparatus shown in (Figure 43).*

Titration

• Unknown concentration can be determined

• Reacting with a standard solution of known concentration and volume in a titration with a substance in solution

Equivalence Point: The point at which the reagents are present in stoichiometric amounts must be easily identified.

Indicators: are added to the reaction mixture is an acid-base and redox titrations.

Construction of Electrochemical Cells

Two types of electrochemical cells that are required to know are electrolytic and voltaic.
Both involve electrodes, electrolytes and a complete circuit with allows electrons to be gained by chemical species at one electrode and lost at the other.

• Electrolytic cells Convert electrical energy into chemical energy

• Voltaic cells Chemical energy is spontaneously converted into electrical energy

Colorimetry and Spectrophotometry

• Spectrophotometry uses a range of UV, visible or radiation.

• Calorimetry is a similar technique that is limited to wave lengths of visible light.

Molecular Models

• Molecular Features that cannot be appeared from the Lewis structures can be from the models.

• It helps us to visualize the three-dimensional structure of a molecule

• Digital models can be easily be saved as files for future reference.

Sensors

Digital devices that can be used to measure physical properties and transmit the results electronically.
Colorimeters and pH probes are examples of digital devices that require frequent calibration (Figure 57).

Spreadsheets

Spreadsheet for manipulating and analysis of large amounts of data
Operators, formulas and function to perform a certain operations with a small selection of simple operators
Operators and functions are summarized in Table 1.

Databases

Digital repositories or large amounts of information, all organized to facilitate retrieval and continuous updates.
Tools 2: Technology

Mathematical Skills

Units

• International Bureau that SI Units should be used and conventions should be followed.

• Space Between a Numerical Value and it Unit.
  Different Units should be separated by a space

A space between a numerical value and its unit.
Decimal markers should be preceded by a number, even if this number is zero.
Different units should be separated by a space.

SI unit for:

*Time
*Energy
*Volume
*Amount of substance.
*Pressure

Uncertainties

*Measurements values that can always be measured exact

Types of Instruments to estimate an instrument

1.Digital( has a scale)
The reading of "1" in the lowest decimal place on the display (Figure 63), the way to estimate an instruments .

2. Analogue instruments have scales marked on them.the estimation the uncertainty is estimated a half the smallest scale division
   Instrument with the more precision gives greater number of the decimal places
   Values the fluctuate the value of some values fluctuate overtime.in these cases the uncertainty can be estimated based on the variation in the values you observed

Further source of Uncertainty

These should be noted by the experimenter for example a thermometer it's a rate is 42 sec and human reaction is the instrument is ± 1s

Express uncertainty in different formats:

1. Absolute

2. Relative

3. Precentage ( the uncertainty is often stated in just only one significant figure)
   Relative uncertainty in the decimal points if the values is the decimal value so it has to show it number points as well.

Decimals placed and significant figure.

A length sample measure with ruler and it has has a specific significant figure. The result of an experiment that always come with calculations that will always equal a specific number that has are two rules of time. Depending on two calculations and how to carry it out
1.Adding and Subtracting- the answer recorded it need to equal the lease number decimal point present it to that the value used

2. multiplying and divide the same process needs carry out as well too it.
   Propagating uncertainty.
   We usually obtains some kind of form of results at the end with the right measurements and the result are going ti have the right uncertainty
   There are three kinds it that are involved in calculating the final measurements

3. the addition (to propagation the uncertainty)and subtraction value ( has to be added abs uncertainty and also the value add it subtract it)

4. multiplication and division if the calculation is used and we need precent we must add all the percentage used.
   With multiplication or division required that an individual calculate the percentage uncertainty first and calculate that values to make calculations.
   Trials that are repeated to that there are repeatable to main and mean at the result.

Graphs and Tables

*Graph that Shows that there are changes affect in an independent and to help to interpret the data between the data .
A graph has a has a different and unseal axis are used to that shows the quality is that those variables are proposal or invers proposal

1. Pie charts are compare of most as percentage of the of the mass and what its total composition contains.
   These tips for helps to to that you do the thing to facilitate a that help when you get it from the data from a data bass when you got of
   Time for a 15 to 20 looking around the database.
   Noting about the search terms and search parameters about that used.
   Organizing a lot data that have it the spreadsheet to that along go.
   Many data bays they tell them to where the origin is in the message.
   These steps shows the graphs has to follow
   Include all the features of a good quality
   Most spreading that has a can be easy when has to plot. the sample
   Some function ally has to mainly to be limited and has to more more particularly when trying to plot different error bars when is drawn on curves
   What kind code needs the must the show the perfect image.
   Graphs is should be to that are high that would it high.
   the graph has to tell when it have the must show for it it has to be shown
   We show it show it to the all the error to to do that easy in the process.
   Lines can used and be to plot if to show if graph do it for it.
   .It means they can it easy it means it be to show
   Show have tell the must it
   Interpretation of a graphs when that the is features the come the from the gradients that are intercepts all the minima.
   Also to use used interpolation extrapolate the to when and some kind of
   When I do to make a the be must to think and what be great what it do and do is I to with that you about great and do. For in when and for think I of
   That for good must
   For 86 show are.

The cofficient value

(Coefficient of Determination, R is a measurements that how value the graph is for. the close points data how is how close it is a successfull and all the data is linear the the the how
The interpretation and is always the to to of value is what to it and data graph a linear the if if

Data and that they'll see have in that

This information or the data you see there of

Sources of experiment

.These values how we have and that always we should and with that show can
Show how is what we to make with that what we and can it
These are and should if that what to it and
All have have show make think should then and. These to code from are is to.
This graph must I the must data good a what what with if am a good
Thank read I is all if what is now and here make you Thank!