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23 Nov 2019

Which of the following would create a supersaturated solution ofsugar and water?
A. Dissolve sugar in water at 95°C up to the solubility limit,followed by cooling the solution to a
temperature of 50°C.
B. Dissolve sugar in water at 50°C up to the solubility limit,followed by increasing the temperature of the
solution to 95°C.
C. A supersaturated solution is made by adding a seed crystal to anunsaturated solution.
D. There is no such thing as a supersaturated solution.

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Elin Hessel
Elin HesselLv2
29 Mar 2019

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Related questions

Multiple Choice Questions

1.) The process of dissolving sugar in water is endothermic but this is not true for all compounds. Dissolving vinegar (acetic acid) in water, for example, is exothermic. Will increasing the temperature increase the solubility of vinegar in water?

(No / Sometimes / Yes), because increasing the temperature ( shifts the equilibrium towards the products / provides more heat for the reaction to overcome the activation energy / shifts the equilibrium towards the reactants / breaks the chemical bonds in vinegar / makes the molecules move faster) and (does not change, increases / decreases ) the solubility of vinegar in water.

2.) The process of dissolving sugar in water is endothermic but this is not true for all compounds. Dissolving vinegar (acetic acid) in water, for example, is exothermic. Which side of the reaction will heat appear for the dissolution of vinegar into water?

a. Heat does not appear in the reaction

b. product side

c. reactant side

c. both sides

3.) For the rock candy to form, sugar needs to come out of solution slowly to allow crystal formation. Would adding more sugar after the heat is turned off be an effective way to create crystals?

Adding more sugar will shift equilibrium toward ( neither reactant or product / aqueous sugar / both reactant and product / solid sugar ). This would ( leave undissolved suager crystals / occur slowly / occur quickly / supersaturate the solution ), so the rock candy ( will / will not ) crystalize well.

bromine br2(l) is more soluble in dichloromethane

Procedure: Setting Up: Add 1.0 g of p-aminobenzoic acid and 10 mL of absolute ethanol to the round-bottom flask containing a stir bar. Stir the mixture until the solid is completely dissolved. Add 1 mL of concentrated [18M] sulfuric acid dropwise to the ethanolic solution of p-aminohenzoic acid, equip the flask with a condenser, and set up the apparatus for heating under reflux using the heating mantle. Reaction: Heat the mixture under gentle reflux for 30 min, stirring all the while. If any solid remains in the flask at this time, remove the flask from the heat source and allow the mixture to cool for 2-3 min. Add an extra 3 mL of ethanol and 0.5 mL of concentrated H2SO4, to the reaction flask and resume heating under reflux. After the reaction mixture becomes homogeneous, continue heating it under gentle reflux for another 30 min. For the experiment to succeed, it is important that all of the solids dissolve during the reflux period. Work-Up and Isolation: Allow the reaction mixture to cool to room temperature and then pour it into a beaker containing 30 mL of water. Basify the mixture to a pH of about 8 by slowly adding 10% aqueous sodium carbonate with stirring. Be careful in this step as frothing occurs during the neutralization. You should calculate beforehand the approximate volume of 10% aqueous sodium carbonate that will be required to neutralize the total amount of sulfuric acid you used. Collect the crude benzocaine that precipitates by vacuum filtration. Use three 10-mL portions of cold water to rinse the solid from the beaker and wash the filter cake. Air-dry the product. Purification: Weigh the crude product and recrystallize from methanol/water pair of solvents: Place the solid in a 50 mL Erlenmeyer flask. Add the minimum amount of hot methanol to dissolve it. Keep on a steam bath. Slowly add hot water to the solution using a disposable pipette just until the solution becomes cloudy and fails to clear up when it is swirled. To the hot solution on the steam bath add hot methanol, drop wise, until the turbidity or crystals just disappear. Allow the solution to cool to room temperature and then cool it in an ice-water bath for 10-15 min to complete crystallization. Isolate the crystals by vacuum filtration, wash them with 5-10 mL of cold water, and allow them to air-dry. Weigh the crystals and calculate the percentage yield.

True or False? When analyzing the IR spectra of starting material and product, a positive indication suggesting that the product was made would be the disappearance of a strong stretch between 1690-1740 cm-1.

True
False

Why is it important that all of the solids dissolve during the reflux period for you to obtain a good yield of product?

A. Because everything needs to be in solution for the reaction to happen to the fullest extent.

B. Because the product will be impure if the intermediate doesn't dissolve completely.

C. Because the ethanol will evaporate off if it's not dissolved.

D. All of the above

What is the gas that is evolved during neutralization?

A. O2

B. CO2

C. SO2

D. CO3

Why is it necessary to neutralize the reaction mixture to work up the product?

A. Because it is dangerous to work with an acidic solution.

B. Because after the addition of ethanol and sulfuric acid, the benzocaine exists as ammonia and must be protonated so that it becomes insoluble and collectable.

C. Because after the addition of ethanol and sulfuric acid, the benzocaine exists as a soluble carboxylic acid and must be neutralized so that it becomes insoluble and collectable.

D. Because after the addition of ethanol and sulfuric acid, the benzocaine exists as a soluble ammonium salt and must be neutralized so that it becomes insoluble and collectable.

If you end up adding 1.5 mL of concentrated sulfuric acid (18 M), how many mL of 10% aqueous sodium carbonate would be required to neutralize the reaction mixture?

A. 1.5 mL

B. 3 mL

C. 15 mL

D. 29 mL

What is the purpose of the sulfuric acid?

A. To catalyze the reaction.

B. To protonate the intermediate salt.

C. To protonate the ethanol.

D. To increase the pH of the reaction mixture.

What is the theoretical yield of the product?

A. 1.00 g

B. 2.98 g

C. 1.20 g

D. 10 mL

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