CHEMISTRY - BROWN 13E BONUS: LAB TECHNIQUES AND...

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CHEMISTRY - BROWN 13E

BONUS: LAB TECHNIQUES AND PROCEDURES

CONCEPT: LABORATORY MATERIALS 1 The laboratory portion of your chemistry course puts into practice some of the concepts you’ll gradually be learning. In this section we will familiarize ourselves with some of the basic apparatuses you’ll be using.

Apparatus Use Apparatus Use

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CONCEPT: LABORATORY MATERIALS 2 Our previous review of laboratory apparatuses dealt with the measuring and transferring of liquids and aqueous solutions. Now we take a look at apparatuses dealing with solids.

Apparatus Use Apparatus Use

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PRACTICE: LABORATORY MATERIALS EXAMPLE 1: If a scientist wishes to measure out exactly 25.0 mL of a 0.100 M HCl solution and add it to a 0.200 M NaOH solution, which instrument would be most useful?

a. Transfer pipet b. Soxlet extractor c. Graduated cylinder d. Volumetric flask e. Buret

Extractor EXAMPLE 2: What is the molarity of a solution made by mixing 200 mL pure water with 100 mL of 0.75 M KCl (aq)?

a. 0.10 M KCl (aq) b. 0.25 M KCl (aq) c. 0.50 M KCl (aq) d. 1.50 M KCl (aq) e. 2.25 M KCl (aq)

EXAMPLE 3: How can a 100-fold dilution be achieved?

a. 1 part solvent to 99 parts solution. b. 90 parts solvent to 10 parts solution. c. 99 parts solvent to 1 part solution. d. 100 parts solvent to 1 part solution. e. 10 parts solvent to 1 part solution.



CONCEPT: EXPERIMENTAL ERROR When any calculation is done there is a level of error involved.

• Error can be grouped into 2 categories: random (lack of ______________) and systematic (lack of ______________).

• Random errors are unpredictable and can lead to results that are either too high or too low.

• Systematic errors are more predictable and can lead to results that are always too high or always

too low, but not both.

• In most cases, a percent error of less than __________ will be acceptable.

%error =Experimental value − Theoretical value

Theoretical value×100

The percent error formula is a useful tool for determining the __________________ of your calculations.

• The _________________ value is your calculated value, and the _________________ value is your known value.

EXAMPLE 1: Which of the following features are indicative of random errors? i. Doing numerous measurements and taking the average in order to minimize any errors. ii. The results of an experiment are consistently greater than expected or less than expected. iii. Refining the parameters of the experiment help to eliminate any errors. iv. The exist of the error is hard to determine.

EXAMPLE 2: Which of the following represent a systematic error when measuring the mass of an anhydrous object? i. You weigh the object before all the water has evaporated. ii. The scale used has not been properly calibrated. iii. Airflow near the balance causes the precise mass to vary. iv. You write down the incorrect mass of the anhydrous object.



CONCEPT: MIXTURE SEPARATION – DISTILLATION & FLOATATION 1 In order to separate the different components of a mixture it must be ______________________.

• In this form each component maintains its individual ________________ properties. • Chemical reactions rarely produce a single, pure product so these types of mixtures are common.

Distillation

This technique involves the separation of liquids and or gases based on a difference in their boiling points. There are many types of distillation methods, but the two most common forms are simple and fractional distillation.

_________________________ Distillation _________________________ Distillation



CONCEPT: MIXTURE SEPARATION – CHROMATOGRAPHY Chromatography

This technique involves the separation of components within a mixture because of a difference in molecular attractions.

• In the procedure a mixture is spotted on a silica plate and the progression of the components on that plate is based on their affinity to the solvent or the plate itself.

• Phase – represents the silica plate, which holds the mixture.

• Phase – represents the solvent, which moves up the silica plate. Moves up by capillary action.

The distance traveled by the components is a method we can use to an Rf value, which helps in the identification of the compound.

Rf =dis tance traveled by compounddis tance traveled by solvent



CONCEPT: MIXTURE SEPARATION – FILTRATION & EVAPORATION

Filtration

This technique involves the separation of a(n) ______________ from a ___________ by its movement through a filter.

• The ____________________ is left behind on the filter paper and is termed the __________________.

• The solvent passes through the filter paper and is termed the __________________.

Example: Use a coffee filter to separate the coffee flavor from the coffee beans.

Evaporation

This technique involves the separation of a ___________________ from a _______________ based on the boiling point of the solvent.



CONCEPT: MIXTURE SEPARATION – EXTRACTION

Under extraction we have the separation of a ______________ and a ______________ .

• Removal of a component from a mixture by selective __________________ in a new solvent.

_________________ extraction is the most commonly used form.

• pH of the system is selectively varied by adding strong/weak base

• Depending on the pKa of the component, its solubility in the aqueous and organic solvent will change (i.e. creation

or removal of a charge by protonation/deprot.)

• Formation of an ion = increased solubility in the _______________ solvent layer.

• Non-ionic form = increased solubility in the _________________ solvent layer.



PRACTICE: MIXTURE SEPARATION – EXTRACTION

Whenever you do an acid-base extraction typically it is better to add a __________ base before a __________ base.

• This allows you to only isolate the ____________ acid (by ↑ aq. solubility)

Organic Layer 0.25 M NaHCO3

Organic Layer 0.25 M NaOHH3O+

H3O+

Organic Layer 0.25 M HCl

OH–

CH3CH2CH3 CH3NH2 HC6H5O CH3COOHpKa = 60 pKa = 10.64 pKa = 9.88 pKa = 4.74



CONCEPT: TEST FOR ANIONS

A chemical reaction occurs when a solid, liquid or gas is formed. Besides these phases being formed ions will also exist within solution. Below are the useful tests that can be employed to identify them.

Anion Application Observation(s)

Chloride ion (Cl –)

To a solution mixture add HNO3 followed by AgNO3.

Bromide ion (Br –)


Iodide ion (l –)


Carbonate ion (CO32-) and Bicarbonate ion (HCO3–)

Adding hydrochloric acid, HCl.

Sulfate (SO42-) and bisulfate (HSO4–)

Adding hydrochloric acid followed by barium chloride, BaCl2.

Sulfite ion (SO32-) Add hydrochloric acid

Nitrate ion (NO3–) Add cold iron (II) sulfate, FeSO4 followed by sulfuric acid, H2SO4.



CHEMISTRY - BROWN 13E BONUS: LAB TECHNIQUES AND...

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