Lab techniques AP Chem Rev.pptx

AP Chem Lab Techniques and

Analysis Tools Review

2 FRQs based on lab data and experimental

design!

Preparing Solutions

•

Molarities by diluting

•

(you should be able to explain how to make a

new solution and chose the correct tools to

use to make these solutions)

–

Aqueous to aqueous

–

Solid to aqueous

•

ALWAYS measure volumes in pipets, burets or

Example:

Data Analysis

•

If given data from a lab experiment, you should be

able to figure out what experiment was performed

and why. This will help you figure out what types

of calculations you must perform to analyze the

data and answer the questions in the FRQs.

–

Pressure, volume data = gas laws (PV=nRT)

What to do if

Use the last heating mass and figure out what to subtract

from it to determine a mass

(a) Calculate the mass of the blue crystals at the start of the

investigation.

What to do if

What to do if

What to do if

Figure out which will go thru oxidation and which thru reduction.

Remember that the greatest (most positive cell potential) is

reduced at the cathode (red cat) and the lowest (most negative cell

potential) is oxidized at the anode (an ox).

What to do if

What to do if

What to do if

Spectroscopy

•

Many different types, each will be outlined

with an example of data.

•

In a “nutshell” spectroscopy works by utilizing

electrons (sometimes ions) and their ability to

absorb and release energy, this energy can

then be analyzed.

•

Main types

: mass spectrometry, emission

Mass Spectrometry

• Intensity of the peaks

gives us relative %

abundance.

• Which Cl isotope is

more abundant?

Emission Spectroscopy

•

Used to determine energy emitted by

electrons within atoms. Can also be used to

probe electronic structure; also can be used as

a means to identify unknowns since each

Infrared Spectroscopy (IR)

•

IR is associated with transitions in molecular

vibrations and can also be used to detect the

presence of different types of bonds. It is

Photoelectron Spectroscopy (PES)

•

Used to prove existence of the “shell model”

of the atom and electrons residing in regions

of different energy (eg. 1s, 2s, 2p all have

different energies associated with them at

different distances from the nucleus)

•

(You have a PES packet that would be good to

review!)

•

Coulomb’s Law and nuclear charge

are used

Data from PES

•

Peaks with more “Binding Energy” are held

tighter to nucleus than valance electrons.

Intensity of the peaks relates to how many e-

are found in each sublevel.

•

E- tightly bound have more nuclear charge

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B i n d i n g E n e r g r y ( M J / m o l e )

2 4

6 8

1 0

0 . 9 0 1 1 . 5

Importance of PES

•

PES provides evidence of the existence of

Spectrophotometry

•

Use of visible light to determine the

concentration of solutions. Only works for

solutions of color. Based on light absorbed (or

transmitted) through an unknown solution, its

concentration

can be determined.

•

*You did a lab where you used a spec to

First step in spectrophotometry is

to pick the correct wavelength to

measure your sample.

Set spec to that wavelength.

Make various dilutions of your

sample to analyze, stick them in the

machine and collect absorbance

data.

Other types of Experiments

•

You should be familiar with the following lists

of laboratory techniques/experiments and the

purpose for performing each type of

Separation Techniques

1. Filtration – separate a solid product from a liquid

(also sometimes called gravimetric analysis)

2. Distillation – purify or collect a liquid from a

liquid by difference in boiling points

3. Chromatography – prove existence of different

substances in an aqueous mixture using IMFs

4. Electrolysis – separate elemental components

Separation of a Mixture

Separation of a Mixture

Separation of a Mixture

What do you do if…

Separation of a Compound

The Electrolysis of water

Water



Hydrogen + Oxygen

H

O



H

+ O

Reactant



Products

Compounds must be

separated by

chemical

means.

Calorimetry

•

Used to measure heat of chemical reactions, a

Styrofoam cup is the most common calorimeter

used.

•

System and surroundings do opposite, must

switch the sign of the surroundings to be the

system’s heat.

•

Use: q = mCΔT formula

Experiment Set-up

•

Data gathered is usually

temperature and time

•

Should also have masses

of samples added to one

another.

Titrations

•

Used to determine the concentration of an

unknown solution by chemical reaction.

•

MaVa = MbVb

•

Most commonly used with acids and bases

(this is the way you performed this lab)

•

Can also perform a redox titration (no

Titration Lab Set-up

•

Data gathered from a titration

should be volume data and

concentrations

•

Use MaVa = MbVb to

determine unknown

•

Watch out for diprotic acids,

must multiply that side of

formula by 2!

•

Can also generate titration

Acid/Base Titration Curves

•

Be familiar with all

aspects of these curves

•

Strong acid, weak acid,

•

Strong base, weak base

•

Equivalence point and

half-equivalence point

(weak)

Example: Collecting gas over water

Gas Collection

First find the P

O2

from:

P

T

= P

H2O

- P

O2

Then use PV = nRT to

find n

Volume of gas collected?

Error Analysis Using Data

The accepted value and the experimental value

do not agree. If the calorimeter leaked heat

The reaction is known to be first order with respect to bleach. In a

second experiment, the student prepares solution of food coloring and

bleach with concentrations that differ from those used in the first

experiment. When the solutions are combined, the student observes

that the reaction mixture reaches an absorbance near zero too rapidly.

In order to correct the problem, the student proposes that following

three possible modifications to the experiment.

Good “buzz words”

•

Polarizable

– large elements have more

electrons, can be used to explain LDFs of larger

elements or molecules

•

IMFs

– good explanation of higher BP of

molecules, always explain acronym before

using! (LDFs, Le Chat…)

•

Nuclear charge

– good explanation of higher IE

or smaller radius of ions, atoms, molec.

•

Coulomb’s Law

– good explanation of lattice

Any thing else…..

Always explain things at the molecular level, don’t just say

increasing temperature increases rate – explain why? KE,

collisions…

If given two substances to compare (IMFs for instance) be

sure to reference them both in your response

IF in doubt, always provide more info than needed! Give

background, never make assumptions, explain what you are

assuming in your FRQ response.