Exam I Flashcards
(57 cards)
True or False
When the flame is yellow, open the air control valve
True
True or False
When the flame jumps, close the gas control valve
True
In the “Basic Laboratory Operations”, what is the purpose of rolling the solid in the cylinder
Remove any air bubbles that are trapped or that adhere to the solid
What does “TD” on a pipet stand for
To Deliver
The mass of a beaker is 5.333g. After addition of 5.00mL of saltwater using a volumetric pipet, the mass of the beaker is now 11.229g. What is the density of the salt water (g/mL).
A) None of the above
B) 1.1800
C) 1.180
D) 1.18
D; This is the answer due to the sig figs.
A student’s pipet is not clean, and a few drops of water cling to the inner wall of the pipet during a density experiment. What effect will this technique have on the reported density?
A) Reported density will be as expected
B) Reported density will be higher than expected
C) Reported density will be lower than expected
D) None of the above
C; this is because it will most likely increase the mL part of the density equation, cause the mL/volume to be higher than the expected grams, making density small
For the “Synthesis of Potassium Alum” lab, what step must be performed in the hood
A) Addition of sulfuric acid
B) Addition of potassium hydroxide
C) The vacuum filtration
D) The gravity filtration
B
For the “Synthesis of Potassium Alum” lab, the reaction of KOH with the aluminum pieces requires it to be heated in order for the reaction to start. Is this reaction….
A) Endothermic
B) Exothermic
B; The reaction itself is exothermic, the part of the question talking about the pieces being heated is just there to throw you off. When the pieces are heated, that’s when they release the gases
For the “Synthesis of Potassium Alum” lab, what is the purpose of the gravity filtration step (Step A3)
A) To concentrate the solution
B) To remove impurities
C) To purify the product
B; Filtration filter things out
For the “Synthesis of Potassium Alum” lab, the aluminum sample is not cut into small pieces, but rather left as one large piece. Will the percent yield of your alum be….
A) Too high
B) Too low
C) Unaffected
C; The only that changes between cutting it up or leaving it in a ball is the rate of the reaction. The percent yield would still be the same
For the “Synthesis of Potassium Alum” lab, if 22.5g of Alum are recovered from a reaction with a theoretical yield of 50.25g, what is the percent yield.
A) 97.59%
B) 44.77%
C) 102.46%
D) 68.41%
B; 22.5/50.25 * 100
For the “% Water in a Hydrated Salt” lab, weighing your salt when it is not completely cooled to room temperature after heating it to remove the water in this experiment can change the apparatus weight of your sample….
A) True
B) False
A; Common sense
For the “% Water in a Hydrated Salt” lab, you can use beaker tongs for handling the crucible in this experiment…..
A) True
B) False
B; You use crucible tongs for handling crucibles, not beaker tongs
For the “% Water in a Hydrated Salt” lab, after drying your salt to remove the water with the first heating, what is the max. difference between the mass of the sample before and after the second heating is allowed to be considered constant?
A) .001g
B) .010g
C) .100
D) 1.00g
B; Just think that for final measurements, that is the only time it is allowed to be .001g off. Since this is in between measurement, you can only be .010g off.
For the “% Water in a Hydrated Salt” lab, what is the most likely reason it is important to check your crucible for hairline cracks prior to the experiment?
A) Some of your sample can be lost in the cracks when it is heated with a Bunsen burner
B) Small cracks can cause the crucible to crack when heated on a Bunsen Burner
C) The flame from the Bunsen burner can superheat the portions of the sample that lie near the crack
B; The heat will start to make the crack spread and cause a risk the the crucible to crack
For the “% Water in a Hydrated Salt” lab, if the hydrated salt molecules are not completely removed from the salt in the heating process will the reported percent water be….
A) Too High
B) Too Low
B; You could think of it as…the hydrated salt molecules would be absorbing the water in the salt, therefore if they aren’t completely gone, the water would be lower than expected.
For the “Carbonate Analysis” lab, why do use Alka-Seltzer in this experiment?
A) Generate experimental levels of CO2
B) Increase the reaction rate
C) Prevent the loss of CO2 to the water
D) To create a vaccuum
C
For the “Carbonate Analysis” lab, what might happen if you don’t invert the tube with the HCl slowly…
A) Bubing from the generator may pop off
B) Vaccuum might be broken
C) CO2 might escape into the water
D) Mass of the sample in the generator might be lost
E) Sample might be containminated
A
For the “Carbonate Analysis” lab, the rubber stopper has a small “crack” resulting in not a tight seal on the burette. How will this affect the calculated the molar volume of CO2?
A) Too high
B) Too low
C) Unaffected
B
For the “Carbonate Analysis” lab, vapor pressure is 750 Torr. The vapor pressure of water is 25 C is 24 Torr. What is the pressure of the CO2 collected over the water?
A) 31 Torr
B) 721 Torr
C) 769 Torr
D) None of the above
D; You would use Dalton’s Law and subtract the 2 numbers
For the “Carbonate Analysis” lab, what are the units for the molar volume of a gas?
A) moles/liters
B) liters/mole
C) grams/mole
D) None of the above
B
For the “Volumetric Analysis” lab, when the pH indicator changes color during a titration, this is considered the…
A) Titration point
B) Equivalence point
C) Stoichiometric point
D) Endpoint
D; The color change is the end of titration (remember that when J2’s thing was pink, that’s when she took the picture)
For the “Volumetric Analysis” lab, All aqueous waste’s from this lab should go in the aqueous waste barrel…
A) True
B) False
False; in the most recent lab that we did, some waste can go down the sink
For the “Volumetric Analysis” lab, The purpose of the burn during this experiment is to prevent making mistakes…
A) True
B) False
False
