Quizzes Flashcards
Safety glasses should not be worn when working in the laboratory.
False
A pipette should be kept horizontally on the bench-top when not in use.
True
Charcoal can be used to remove color contaminants in the sample.
True
Melting point is not an identification technique
False
Give two uses of a pipette.
- To add a solvent drop-wise
2. Filtering
Your dissolved sample is yellow in color and contains sand particles. How can you remove these impurities?
By adding charcoal and boiling chips, then performing a hot gravity filtration.
In micro-recrystallization centrifugation is used. Why?
It is used because the sample is too small to use a Büchner funnel, and the speed of the spinning separates the filtrate and mother liquor based on mass.
State two methods to induce crystal growth.
- Add a formed crystal to act as a “seed”
2. Scrape the side of the flask to create an etch for crystals to grow in.
The crystals collected in the Büchner funnel should be washed with cold water, not with hot water. Why?
Hot water could make the crystals dissolve, and you would lose some of the ones that you collected.
Melting Point of an unknown A = 95-97 C. Following information was obtained from mixed melting point experiments.
A + X = 84-86
A + Y = 90-92
A + Z = 96-98
From the three, which is the unknown compound?
Z
You started with 1.32 grams of an unknown sample and after recrystallization you obtained 0.93 grams of solid crystals. Calculate the percent recovery for the sample.
(0.93g /1.32g) x 100% = 70.45% recovery
Organic waste can be discarded directly into the sink.
False
Chemicals that are kept in the fume hood can be taken out to working stations.
False
You have been provided with an unknown mixture containing the following compounds. What order should the be extracted in?
B-Naphthol, Chlorobenzoic Acid, Fluorene
1 - Chlorobenzoic Acid
2 - B-Naphthol
3 - Fluorene
Write the products:
R-COOH + NaHCO3 —>
RCOO- Na+ + CO2 + H2O
Write the products:
R-COOH + NaOH —>
RCOO- Na+ H2O
Write the products:
Ar-OH + NaHCO3 —>
No reaction
Write the products:
Ar-OH + NaOH —>
Ar-O- Na+ H2O
State whether the following compounds are miscible in water or not.
Hexane, Methanol
Hexane - No
Methanol - Yes
What is the use of a drying agent in an extraction?
Used to remove trace amount of water.
Even though diethyl ether is an effective extraction solvent, is has drawbacks. State 2.
- Highly flammable
2. Highly volatile
You have been assigned to extract compound X (molecular weight 60g/mol). A 100mL solution of water containing 15g of X is provided to you, as well as 40 mL of diethyl ether. Assume partition coefficient Kd = 10.
How do you add the diethyl ether for the highest recovery? Why?
- Add 20 mL of diethyl per each step and extract twice.
- Extracting twice will give the highest rate of recovery, since the second extraction will remove some of the compound that was in the organic portion to the aqueous portion.
In TLC, compounds are separated according to polarity.
True
Safety glasses should not be worn at all times during the lab.
False
Iodine jars should not be taken out of the fume hood.
True
Chromatography is a separation technique.
True
What are the two phases in a TLC experiment?
Stationary and Mobile
For a TLC experiment SiO2 has been used as the absorbent. Is it polar or non-polar?
Polar
Arrange the following compounds in the order of increasing affinity towards the stationary phase.
Chloroethane, Ethyne, Ethanamine, Ethane, Acetic Acid, Acetaldehyde
1 - 6 (Least - Most)
1 - Ethane 2 - Ethyne 3 - Chloroethane 4 - Acetaldehyde 5 - Ethanamine 6 - Acetic Acid
What is the purpose of using a piece of filter paper (wick) in the TLC chamber?
The wick saturates the chamber by letting more of the solvent give off vapors.
What are the 2 visualization techniques used in TLC?
Shortwave UV light and Iodine
Column chromatography is a separation technique.
True
The loaded column should not have air bubble in it.
True
Air pressure can be used to facilitate the solvent flow through the column.
True
Name two compounds that can be used as the polar stationary phase in column chromatography.
SiO2, alumina
What is the force used in column chromatography to percolate the solvent through the column?
gravity
When packing the column with initial sand and alumina layer, it should be done in a way that no air bubble will remain in the layer. Why?
The air bubbles can interrupt solvent flow, which disturbs the even bands of each compound as they flow down.
Write down the simple technique that can be used to achieve a column packing without air bubbles.
After loading each layer, tap the side of the tube so that it settles.
Is petroleum ether polar or non-polar?
Non-polar
