Final

Question 1

Define Calorimetry

Answer 1

Measuring the energy released when burning one gram of something.

Question 2

What is meant by a small calorie (c) and a food calorie (C)?

Answer 2

c is a scientific calorie.

C is food, and it measures the energy in food. It’s made up of 1000 c’s.

Question 3

Define Spectroscopy

Answer 3

The study of light waves interacting with matter.

Question 4

The difference between a line and continuous spectrum and give an example each.

Answer 4

Continuous Spectrum: Is when a light that is emitted through an entire spectrum (ex: sunlight)
Line spectrum: emits a few frequencies and colors. (ex: Hydrogen gas)

Question 5

What kind of energy transitions occur in emission and absorption?

Answer 5

Electronic transition.

Question 6

What is white light? What’s it’s wavelength range?

Answer 6

Visible Light.

450nm to 700nm

Question 7

List the colors of the spectrum from the highest to the lowest frequency.

Answer 7

Violet blue green yellow orange red

Question 8

What is the purpose of the discharge tube?

Answer 8

When turned on, gas particles become excited and emit light that can be observed through a spectroscope and then measured the wavelength.

Question 9

How does the spectrum change with:

a) The slit width
b) The distance from the source of light to the spectroscope

Answer 9

a) Changes the size of the spectral lines

b) Changes the intensity of the light

Question 10

How was the spectroscope calibrated?

Answer 10

On a graph I put 3 dots that corresponded with 3 spectral lines, drew a line a through them and calculated the equation of a line.

Question 11

What is the complementary nature of absorbed/observed colors?

Answer 11

When a color is absorbed, the opposite the color is observed.

Question 12

What is the main reason a substance absorbs light?

Answer 12

Radiation’s energy moves electrons from the low energy state to high energy sate.
An electron jumps to a specific wavelength which corresponds to electron transmission energy.

Question 13

Describe the technique of colorimetry?

Answer 13

A process where a set of solutions of known concetration of some light absorbing substance is placed in a series of containers. Unknown concentration solution can be determined by comparing with the calibration set.

Question 14

What process removes the energy from excited food dye molecules in aqueous solution?

Answer 14

The extra energy is continuously transferred by solvent molecules bumping against food dye molecules

Question 15

The dilution equation?

Answer 15

MV=MV

Question 16

Describe the OTO observations

Answer 16

Tap water was mixed with OTO to turn yellow and be able to observe heavy chlorine presence.
The Brita filter lowers the concentration of Cl, lighter color cuz of the carbon.

Question 17

Why is aluminum expensive to produce?

And then give two uses for the alum compound you synthesized.

Answer 17

1-Because the hall-herault process is extremely energy intesive and 2-most high-grade bauxite deposits occur outside the US.
1-making paper and 2-cosmetics.

Question 18

What’s an Alum?

Answer 18

Hydrated double salt, usually Aluminum sulfate/

KAl(SO4)2*12H2O

Question 19

When H2SO4 is added to one of the scratched up areas of an aluminum can bubbles are observed. write a reaction to explain this observation.

Answer 19

2Al(s) + 3H2SO4(aq) ==> 3H2(g) + Al2(SO4)3 (aq)

The bubbles form because of the H gas.

Question 20

Write an equation which explains carbonated beverages are acidic?

Answer 20

CO2+H2O==>H2CO3
OR H+HCO

(Acidic due to H)

Question 21

How did you test for the presence of SO4,K,Al,H2O?

Answer 21

SO4:BaCl2 was added to react with the sulfate ion (white precip. forms)
K: Flame test. Color was pink/violet.
Al: KOH was added to Al(OH)3 was produced
H2O: Cracked when heated.

Question 22

You did a melting point test on the alum you made. What two things does this test tell you about your compound?

Answer 22

1-It clarified how pure the alum was

2-It confirmed the identity.

Question 23

Draino reaction.

Answer 23

Al2O3(s)+2KOH+2H2O ==> 2KAl(OH)4

Question 24

Explain “Like dissolve like”

Give example

Answer 24

Identical IMF’s = dissolve.

Ex: H2O+HN3 (LDF & H-bonding)

Question 25

Use the like dissolve like principle to explain the solutbility experiments you did with water, kerosene, ethanol, pentanol

Answer 25

Water: Polar by structure
Kerosene: Added to water. Runs off. Nonpolar
Ethanol: Added to nonpolar kerosene. Doesn’t mix. Polar.
Pentanol: In water it will separate but not fully dissolve. So partially pressure.

Question 26

Write out the chemical explain the following:
1-Why aqueous Sodium Carbonate is basic

2-Why Aluminum chloride is acidic.

3-Why pottasium iodide is neutral

Answer 26

1-Na2CO3 + H2O => HCO3 + OH + 3Na

2-Al+H2O => Al(OH) + H

3-KI + H2O => KOH + HI

Question 27

Why is aqueous ammonia/ammonium hydroxide called that?

Answer 27

Ammonia can react with water to form ammonium hydroxide.

NH3 + H2O ==> NH4OH

Question 28

4 major types of chemical reactions in aqueous solutions.

Answer 28

1-Precipitation: Produces new compound that’s not soluble in aq. sol.
2-Acid-base: formation of covalent, and water and salt.
3-Complexation: One or more covalent bonds are produced in the formation of the product.
4-Redox: Electrons are reduced and oxidized.

Question 29

Solubility rules?

Answer 29

Soluble: NO3, SO4, Cl, Br, I (OH, PO4, CO3 only with Na, K)
Insoluble: OH, PO4, CO3

Question 30

Why is a BTB indicator better than the red cabbage indicator?

Answer 30

Cuz BTB is synthesized so we know it’s in it. More accurate

Question 31

The diffference between the single well and serial titrations.

Answer 31

Single Well: 1 well. dd known M, and then add unknown until reading the endpoint.
Serial: Well strips. Add drops of known M serially. Then add a solution unknown and see where an equivalence point is melt.
Single well is easier and faster.
Serial is more accurate.

Question 32

You did some titrations of HCl with NaOH, using a BTB indicator. What is observed at the endpoint, and what is the overall and net ionic equation? You should also know how to calculate the concentration of an unknown given titration results.

Answer 32

HCl+NaOH==>NaCl+H2O
H+OH==>H2O

The BTB turned from yellow to blue

MV=MV

Question 33

1-What is back titration.

2-Why is this a better approach than a regular titration for the analysis of calcium carbonate in egg shells.

Answer 33

To add an excess of acid to completely dissolve CaCO3 and then titrating the unreacted acid with soluble base.
2-It’s easier and faster.

Question 34

Why is hard water a problem?

Answer 34

1-scale formation in industrial boilers.

2-narrowing pipes.

Question 35

Why is a buffer necessary in EDTA method?

2-And why does each sample need to be spiked with MgEDTA?

Answer 35

1-Breaking down Mg and Ca

2-Turning water red to be able to observe color change.

Question 36

Formula to calculate water hardness with EDTA results

Answer 36

1x10^-3 mol caco3 * 100gcaco3 * 1000mgCaco3 = 100ppm

Question 37

What is the purpose of the “standards” that are run as part of an AA analysis?

Answer 37

To test how good the calibration graph is to the concentration value in ppm.

Question 38

What is the problem with analyzing a sample whose absorbance exceeds 1 absorbance unit? What is sometimes done in this experiment to compensate for this problem?

Answer 38

Theoritically, a substance canot absorbe over 100 percent.

Usually a sample is diluted 50 percent with water in this problem.

Question 39

How to convert Ca and Mg to hardness with AA results?

Answer 39

ppm multiplied by 100gcaco3 over molar mass