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Experiments 1-6

Purpose of an Exhaust Hood

It has a fan to exhaust fumes out of the hood and away from the user

When is an exhaust hood used?

When studying noxious, hazardous or flammable materials

Which is correct? Pouring acids into water or water into acids?

Pour acids into water

Why do you pour acids into water (not the other way around)?

Because the heat of solution will cause the water to boil and the acid to splatter

Which common reagents are highly flammable?

Alcohols, acetone and ether

What does SI stand for?

International System of Units

Unit for Mass or Weight

gram

Gram

1 cubic centimeter of water at 4*C and 760 mmHg

Mass

quantity of material

Weight

mass times gravitational force

Unit for Length

meter (m)

1 meter = __ cm = __ mm = __ in.

100, 1000, 39.37

Unit for Volume

Liter

Liter

volume of 1 kg of water at 4*C

Unit for Temperature

*C

Temperature

measures heat intensity

Conversion between C andF

(9/5)C = F - 32

Unit for Heat

calorie

Calorie

the amount of heat required to raise 1 gram of water 1*C

1 cal = ____ J

4.184

Density for Liquids

g/mL

Density for Gases

g/L

Density for Solids

g/cm^3

Density

mass / unit volume

Specific Gravity

sp gr = density of a substance / density of a reference substance

Femto-

10^-15

Pico-

10^-12

Nano-

10^-9

Micro-

10^-6

Milli-

10^-3

Centi-

10^-2

Deci-

10^-1

Kilo-

10^3

Mega-

10^6

Giga-

10^9

SI Unit for Length

meter

1 inch = ___ cm

2.54

SI Unit for Volume

cubic meter (m^3)

1 L = __ cm^3 = __ m^3 = __ qt

1000, 0.001, 1.06

SI Unit for Mass

kilogram

1 kg = __ g = ___ lb

1000, 2.205

1 lb = ____ g

453.6

SI Unit for Energy

Joule (J)

SI Unit for Temperature / Conversion to *C

Kelvin (K)
*C + 273.15

What is the purpose of a lab balance?

It is used to obtain the mass of various objects.

What are graduated cylinders? What do they measure?

Tall, cylindrical vessels with graduations scribed along the side of the cylinder; measure volume

What is more accurate: a tall cylinder with a small diameter or a short cylinder with a large diameter?

A tall cylinder with a small diameter

What principle are thermometers based on?

Liquids expand when heated

What liquid is inside common thermometers?

Mercury or colored alcohol

How are thermometer calibrated?

Measure 2 temps - BP of water and FP of water then divide the distance between those two temperatures into respective numbers (so between 0 and 100*C there would be 100 divisions)

What are pipets?

Glass vessels that are constructued and calibrated so as to deliver a precisely know volume of liquid at a given temperature

To what place is mass recorded from an analytical balance? From a top-loading balance?

0.0001, 0.001

Is the meniscus in a graduated cylinder convex or concave?

Concave

How do you correct temp of BP of water?

(760 mmHg - atmospheric pressure) (0.037C/mm)

What is the true BP after temperature correction?

100 - (BP correction) = ___ *C

Net weight =

gross - tare

What is the precision of a measurement?

A statement about the internal agreement among repeated results; a measure of the reproductibility of a given set of results

What is the simplest measure of precision?

The average deviation from the mean

How is the average deviation calculated?

sum of |value - mean| / number of values

1 mL = ____ cm^3

1

An object weighs exactly 5 g on an analytical balance that has an accuracy of 0.1 mg. To how many significant figures should this mass be recorded?

5.0001 - 5 SF

What is chromatography?

A technique by which the components of a mixture, dissolved in a fluid solvent, are separated through differences in adsorption to a solid surface (components of a mixture are separated)

Chromatography: as the fluid is passed through the solid...

The stronger the interaction of the components with the solid surface, the slower the components pass by or through the solid compared to the solvent

How is the water wicked through the paper in paper chromatography?

Capillary action

The stronger the components of the mixture interact with the cellulose of the paper, the ____ distance the components will travel along the paper.

Smaller

Retention Factor

Rf = distance traveled by spot / distance traveled by solvent front

What "water" is used for paper chromatography?

0.1 NaCl

Common Dyes

Blue #1, 2
Yellow #5, 6
Red #3, 40
Green #3

Why would the Rf values vary?

Temperature and other variables

Chromatography - General Procedure

1. Use a medicine dropper to place a drop of water on top of each piece of candy. Wait 10 minutes for water to dissolve dyes.
2. Put NaCl in a beaker (just enough to cover bottom).
3. Label chromatography paper.
4. After transferring dye to chromatography paper and letting it dry, put it in the beaker with line of dyes facing the NaCl
5. Don't let filter paper touch sides. Cover with saran wrap. Wait until NaCl travels to 1 cm from the top.
6. Remove paper. Record distances traveled by solvent and by dyes.

Why is it important to use a pencil and not a pen when doing the paper chromatography experiment?

The ink from a pen may travel up the filter paper in a similar fashion as the dye.

What do you think might happen during the solvent migration up the paper if the two long edges of the filter paper overlapped when made into a cylinder?

The molecules would interfere and the paper would also interact with the glass.

What is the purpose of the Percent Water in a Hydrated Salt Experiment?

To determine the percent by mass of water in a hydrated salt
To establish the formula of a hydrated salt

What does it mean when a salt is hydrated?

A number of water molecules are chemically bound to the ions of the salt in its crystalline structure

Water molecules that are chemically bound to the ions of the salt are called...

Waters of Crystallization

Is the number of moles of water per mole of salt constant or variable?

Constant

Formula for hydrated iron (III) chloride

FeCl3 * 6H2O

Formula for hydrated copper (II) sulfate

CuSO4 * 5H2O

What is an anhydrous salt?

A salt without water; the water molecules are so loosely bound to the ions that heat removes them to form this

Efflorescent

Hydrated salts that spontaneously (without heat) lose water molecules to the atmosphere

Deliquescent

Hydrated salts that readily absorb water

What is the formula for epsom salt?

MgSO4 * 7H2O

Can anhydrous FeCl3 form? Why or why not?

No, because the water molecules are so strongly bound to the salt that it cannot form regardless of the intensity of the heat

Percent by mass of water in the salt:

grams of water (# moles H2O 18.01g/mol) / grams of hydrated salt 100%

Gravimetric Analysis

An analytical method that relies almost exclusively on mass measurements for the analysis

What method does the Percent Water in a Hydrated Salt experiment use? How?

Gravimetric analysis; the mass of a hydrated salt is measured, the sample is heated to drive off the waters of crystallization, and the mass of remaining sample is measured again. Cycles of heating and measuring of the sample's mass are continued until reproducibility of the mass measurements is attained.

What materials are needed for the Percent Water in Hydrated Salt experiment?

Crucible and lid, tongs, bunsen burner, utility clamp, clay triangle, calculator, desiccator, balance

What is the general procedure of the Percent Water in a Hydrated Salt experiment?

Prepare a clean crucible by heating on a clay triangle
Determine the mass of the sample
Put the sample in the crucible and heat slowly and gradually
Cool in a desiccator
Measure the sample (crucible and lid first then with sample - subtract)
Reheat. Cool in a desiccator.
Re-measure the mass. If it's within 0.010 grams, you're good

Why can CaCl2, a deliquescent salt, be used as a desiccant in laboratory desiccators?

Deliquescent salts readily absorb water. Desiccators are used to remove any excess water before mass measurements. CaCl2 is a suitable desiccant because it helps remove some of the water from the crucible and sample before mass measurements.

What is the purpose of firing the crucible in the Percent Water in a Hydrated Salt experiment?

Get rid of any condensation that is naturally from the air in the lab

How does the use of crucible tongs in the experiment maintain the integrity of the analysis?

If you use your fingers, the oils from your fingers will interfere with the amount of condensation on the crucible and in the sample (the mass of the water will be too high)

Why are mass measurements performed only at room temperature?

the scales were likely calibrated at room temperature. thermal expansion can cause them to give false readings especially if you are taking very accurate measurements.

Why is the position of the crucible lid critical to the dehydration of the salt during the heating process?

If the lid were placed directly on to the crucible, the water would not be able to escape. This would result in accurate mass measurements because the sample would still be hydrated.

Percent water in the hydrated salt =

mass of hydrated - mass of anhydrous / total mass of hydrated salt * 100

Heat of Reaction / Enthalpy Change

the energy change of a reaction that occurs at constant pressure

Enthalpy Change Symbol (written out)

delta H

If heat is evolved, the reaction is __________.
If heat is absorbed, the reaction is ________.

exothermic, endothermic

What is the heat of neutralization?

The enthalpy of neutralization, or the change in energy, when an acid and a base react to form water.

What is a calorimeter?

A thermally insulated vessel

The heat liberated in the neutralization will cause a(n) ________ in the temperature of the solution and of the calorimeter.

increase

If the calorimeter were perfect, _____ would be radiated into the lab.

NO heat

What is the heat capacity of the calorimeter?

The amount of heat (the number of joules) required to raise its temperature 1 K, which is the same at 1*C.

Change in enthalpy, delta H =

negative (-) product of the temperature change, delta T, times the heat capacity of the calorimeter and its contents

= -deltaT (heat capacity of calorimeter - heat capacity of contents)

Because delta H is negative for an exothermic reaction whereas delta T is positive, a ____ sign is required in the deltaH equation

negative

How is the heat capacity of the calorimeter determined?

By measuring the temperature change that occurs when a known amount of hot water is added to a known amount of cold water in the calorimeter. The heat lost by the water = heat gained by the cold and the calorimeter. Assume no heat is lost to lab.

Heat lost by warmer water =
(Use and define variables)

(T2 - Tf) mass specific heat
T2 = temperature of the warmer water added to it
Tf = temperature after mixing

Heat gained by colder water =
(Use and define variables)

(Tf - T1) mass specific heat
Tf = temperature after mixing
T1 = temperature of a calorimeter and the cooler water

Heat lost to the calorimeter =

(heat lost by warmer water) - (heat gained by cooler water)

Heat lost to the calorimeter =
(Condensed equation)

(Tf - T1) * heat capacity of calorimeter

Heat of reaction =

(heat gained by the solution) + (heat gained by the calorimeter)

General Procedure for Heat of Neutralization

1. Construct a calorimeter (2 coffee cups inside one another, lid, thermometer with stopper so it doesn't touch bottom)
2. Measure base and add it to the calorimeter. Place lid (without thermometer) on top.
3. Measure out acid into a dry beaker. Let stand. Measure temp.
4. Insert thermometer into calorimeter. Measure temp of base. (base and acid should be +/- 0.5*C)
5. Add acid to base. Record temp every 15 seconds for 3 minutes while stirring.
6. Construct a temp vs. time curve and determine deltaT.

Purpose of Heat of Neutralization Experiment

Calculate deltaT and the heat of neutralization per mole of water formed

Define the term heat capacity.

The amount of heat (the number of joules) required to raise its temperature 1 K, which is the same at 1*C.

Define the term specific heat.

The heat required to raise the temperature of 1 g of a given substance by 1*C.

What is the difference between heat capacity and specific heat?

Heat capacity is more general; specific heat is for 1 g

Describe how you could determine the specific heat of a metal by using the apparatus and techniques in this experiment.

Obtain and weigh a metal.
Put it in boiling water and record its temperature.
Record the temperature of room temp water in a calorimeter.
Place the metal in the calorimeter once the temperatures are about equivalent.
Plot temp vs. time on a curve to determine deltaT and use the respective equations to determine specific heat -- Q = m(Cp)(deltaT) or (heat gained by water) / (heat lost by metal)

Neutralization

reaction of an acid with a base; forms water

Neutralization Reaction

H3O+(aq) + OH-(aq) --> 2H2O (l)

Purpose of Neutralization Reaction

To determine the concentration of a prepared base solution

Define standardization.

The process of determining the concentration of a solution

General Procedure of Titration of Acids and Bases

1. Standardize the base (NaOH) solution
2. Measure the volume of standardized base that is required to exactly neutralize the acid present in the unknown.
3. Use an indicator solution to determine when an acid has exactly neutralized a base (or vice versa)

Purpose of Titration of Acids and Bases

To determine the amount of acid in an unknown

Define titration.

The technique of accurately measuring the volume of a solution required to react with another reagent.

Define end point.

The point (immediately after the equivalence point) where the color changes, signifying that the base has completely neutralized the acid or vice versa.

When does a suitable indicator change color?

When equivalent amounts of acid and base are present

Example of an indicator

phenolphthalein (pink at a pH of about 9)

What is the formula for potassium hydrogen phthalate?

KHC8H4O4 (abbreviation: KHP)

How many acidic hydrogens does KHP have?

1 -- monoprotic acid

What is the molar mass of KHP?

204.2 g/mol

What is the balanced equation for the neutralization of KHP?

KHC8H4O4(aq) + NaOH(aq) --> H2O (l) + KNaC8H4O4(aq)

Define equivalence point of titration.

The point at which stoichiometrically equivalent quantities are brought together; a theoretical point determined qualitatively

Molarity units

moles solute / volume of solution liters
10^-3 mol (mmol) / 10^-3 L (mL)

% KHP =

(g KHP / mass of sample) * 100

What is parallax and why should you avoid it?

The effect of failure to level eyes with the bottom of meniscus; avoid it because it creates inaccurate readings and results

Why is it necessary to rid the distilled water of CO2?

CO2 dissolved in water creates H2CO3 (acid)

Identify each of the following as measurements of length, area, volume, mass, density, time or temp:
ns; kg/m^3; pm; 750 km^2; 83K; mm^3

time, density, length, area, temperature, volume

How many sig figs?
5.231 * 6.1
72.3/1.5
12.21 + 0.0132
31.03 + 12

2, 2, 2 decimal places, 0 decimal places

Describe the method for finding the boiling point of water at 620 mmHg.

(760 mmHg - 620 mmHg) (0.037C/mm)

How do you find standard deviation?

sum of |value - mean| / number of values

What are the two main types of chromatography?

Thin-layer chromatography (TLC)
Column chromatography (CC)

What kind of chromatography did we use?

Thin-layer chromatography (TLC)

What are the uses of chromatography?

- To separate the components of a mixture (TLC and CC)
- To determine the purity of a compound
- To see if two compounds are identical
- To monitor the progress of a reaction

The more polar a molecule, the _____ it goes up the filter paper in chromatography

more slowly

State examples of a polar stationary phase.

Alumina, silica gel, cellulose/paper

What is the mobile phase?

solvent(s) of varying polarity

State examples of a mobile phase.

NaCl, water

Define adsorb.

Come in contact with and integrate themselves into cellulose structure.

How does chromatography work?

Sample is loaded onto polar stationary phase.
Polar compounds will adsorb onto the stationary phase to a greater extent than nonpolar compounds.
Mobile (eluting) phase helps "push" the compounds either down a column (for CC) or up a plate (for TLC)

Define elution.

Process of solvent moving up the paper

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