lab final
(e) What is the cost per oz of acetic acid?
(3.3/5.36)x100 =61.567 =62
**Calculate Delta H_neutzn in joules per mole for the reaction of 1.00 mol of HNO_3 with 1.00 mol of NaOH.
dH = - 2738 J / 0.050 mole dH = -54,756 J /mol your asnswer is: dH = -54.8 kiloJoules
(c) How will you measure the volume of the Erlenmeyer flask
divide by 1000mL
How will you determine whether you need to clean your buret before beginning the experiment?
if there are any water dropplets in the inner surface
The titration of 25.00 mL of a vinegar sample with 0.500 N sodium hydroxide solution required 44.60 mL . Assume the density of the vinegar sample is 1.00g mL b) Calculate the number of grams of acetic acid in the sample.
mass of acitic acid 60 grams 0.0223 x 60/1 = 1.338
A pressed polystyrene top was used to cover the polystyrene cup after the acid and the base solutions had been mixed how it would afect the resuts
nothing as long as the reactants and solvents were ionic
How will you recognize the end point of your titration of KHP solution with NaOH solution?
the pink color will be in the titration mixture
titrant
the standard solution added to the sample in a titration
a student who was in a hurry to complete this experiment didn't completely dry the crystalline product before the final weighing. how would this error affect the calculated percent yield of the experiment?
the weigh will be higher causing a yeild over 100%
the student in (1) didn't bother to cool the water used to wash the crystals. how would this error affect the calculated percent yield of the experiment?
the yeild would go down because warm water might dissolve the cristals
Titration end point
when there is a color change then the end point has been reached
(d) if 16 oz of the vinagar cost 53 cents, what is the cost per oz of vinagar solution?
(53/16)=3.31 cents oz
2. Would the molar mass of a volatile liquid, calculated using the procedure in this experiment, be incorrectly high, incorrectly low, or unaffected by the following procedural changes?
(a) You did not completely vaporize the liquid when you heated it. When not completely vaporized then pressure value was less than actual. As a result, the value of n would be less. Molar mass value would be incorrectly high. (b) The foil cap got wet while you were cooling the flask and its contents with running water. When the foil cap retained some water, increasing the vapor pressure value.making the, value of n would increase and consequently the molar mass value would be incorrectly low. (c) You added the boiling stone to the flask after you had already determined the mass of the empty flask and foil cap. then stones mass was added to the mass of the unknown liquid. As a result, the molar mass value was incorrectly high. (d) You forgot to measure the volume of the flask, so you used the volume printed on the flask for your calculations. Volume measured from the volume printed on the flask was correct and the value of molar mass was unaffected. (e) Your unknown liquid had a boiling point of 102.3 Celsius. If the unknown liquid had a boiling point higher than water then they would never boil a result, pressure value would be low and the molar mass value would be incorrectly high
Explain how the following changes in the procedure for this experiment would affect the results. A) A glass beaker was used instead of a pressed polystyrene cup?
-It insulates causing a more accurate measurement B)
Recalculate your percent yield, taking into account the water solubility of aspirin when you calculate the theoretical yield.
0.0152 x 180/1mol = 2.74 g
The titration of 25.00 mL of a vinegar sample with 0.500 N sodium hydroxide solution required 44.60 mL . Assume the density of the vinegar sample is 1.00g mL a) Calculate the number of gram-equivalents of acetic acid in the vinegar sample.
0.0223 x 1/1 = 0.223 g
Calculate the number of moles of HNO_3 reacting when 50.0 mL of 3.00 M HNO_3 and 50.5f 1.00 M NaOH solution are mixed.
0.05 x 1 = 0.05
How many grams of aspirin were lost in the washing process you used to purify your product, assume you used 50 ml of water for washing? The solubility of aspirin in water is 0.33 g per 100 ml at room temp.
0.33/100 x50 = 0.165 g
Calculate the mass of the reaction mixture. Assume the density of the mixture is 1.03 mL^-1.
1.03 x 100.5 ml = 103.5
The titration of 25.00 mL of a vinegar sample with 0.500 N sodium hydroxide solution required 44.60 mL . Assume the density of the vinegar sample is 1.00g mL c) What is the percent acetic acid in the vinegar sample?
1.338 g -------- x 100 =5.352 % 25 g
A student performing this experiment titrates 1.390 g of KHP with a NaOH solution. The initial buret reading is 0.73 mL and the final buret reading is 22.38 mL. What is the monetary of the NaOH solution? ...
1390 / (22.38-.73 ) x 204.22 = 0.3144 M
Calculate Delta T for the reaction. Assume the initial temperature of both reactants is 25.0 degree C
30.3-25 = 5.3 C
Calculate the volume of the reaction mixture
50 ml + 50.5 ml = 100.5 Ml
On the basis of an accepted Delta H_neutzn of 58.5 kJ mol^-1 for the reaction, determine the percent error in your calculated Delta H-neutzn.
58.5-56 -------- x 100 = 4.3% 58.5
Suppose that, in an attempt to minimize waste, a laboratory teaching assistant decided to give each student only 1 mL of each liquidf for use to measure density in this experiment.
A) (1) Estimate the magnitude of the absolute error and percent error in the measured sample volumes. Compare those errors to the errors that occur when measuring volumes of approximately 8 mL, as is normally done in this experiment Assume that the graduated cylinder used to measure all of the volumes has 0.1-mL graduations. You're save assuming (0.1 / 2) mL error with 0.1 mL graduations, so +/-0.05 mL absolute error, 0.05 mL / 1 mL = 5% relative error in a 1 mL sample. With an 8 mL sample, absolute error is the same but relative error is 1/8 as large (because the sample is 8 times bigger). B) Based on your answer to (1), would you be more or less confident about your density measurement if you used the smaller sample volume, rather than the normal 8-mL sample? Breifly explain more confident knowing it would yield a closer measurment.
Studying an unknown liquid using the procedure of this experiment, a student recorded in table 2 the following data. Table 2 Volume of liquid, ml 8.30 mass of cylinder & liquid, g 45.00 mass of graduated cylinder, g 38.44 Solubility: in water i in cyclohexane s boiling point, �C 80
A) calculate the density: 45 - 38.44 = 6.56 g 6.56/8.30 = 0.79g/ml B) List the liquids in table 2 whose densities and boiling points most closely match those of the unknown liquid. List these liquids densities, boiling points, & solubilities. Propanone methanol ethanol C) Based on your evaluation of all of the data in your answer to (2), including solubilities, identify the unknown liquid. Briefly explain your reasoning. ethanol has a density of 0.789 & 78.5 boiling point and its miscible with H2O and cyclohexane
Briefly explain why the procedure you used to determine boiling point would not work for liquids with boiling point greater than 100 degrees C.
Because it is sitting in water and the boiling point for water is 100 degrees so the water tempurature cannot get any higher.
A student was given only one graduated cylinder to use for this experiment. After using it to measure 50.0 mL of the assigned acid, the student failed to rinse or dry the cylinder before measuring out the 50.5 mL of the base. would the calculated change in Heat Neutralization be higher, lower, or the same as the literature for change in heat neutralization. Briefly explain this difference as a result of using only one graduated cylinder for the experiment.
Calculated H neutzn will be higher since cylinder used without rinsing contains little acid which will react with the base this will make base's strength lesser than the original. & Now when you will do titration (neuralization) the base required will be more than the actual. where actually the base used should be less and actual concentration of H therefore should have been less.
Acid-base indicator
Chemical dyes whose colors are affected by acidic and basic solutions
the same student mixed the crystalline product with ethanolic 1% FeCl3 solution and obtained a colored solution. briefly explain what might have caused this result.
FeCl3 is used to indicate the presence of a phenol by turning purple color. the color change was a result of still having salicylic acid a result of improper heating.
The accepted ΔH neutzn of hydrobromic acid(HBr) reactingwith NaOH solution and HNO3 reacting with potasium hydroxide (KOH)solution are identical. 1. Write net ionic equations to show whataqueous HBr and HNO3 have in common.
H+(aq) + Br- (aq) + Na+(aq) +OH-(aq) ----------> Na+(aq) +Br-(aq) + H2O(l) H+ (aq) +NO3- (aq) + K+(aq) +OH-(aq) ----------> K+(aq) +NO3-(aq) +H2O(l) Net ionic equations H+ (aq) +OH-(aq)----------> H2O(l) H+ (aq) +OH-(aq)----------> H2O(l)
using structures for all species, write the complete esterification reaction begun below: methanol (CH3OH) + salicylic acid ------H2SO4------> ?
H3c-o::-H + []-OH =O-OH + H2O
A student doing this experiment was puzzled by the fact that while each of the individual solutions being used is dangerous the mixture could be safely disposed of by pouring it into the drain and diluting with a large amount of running water. Describe the hazards of each of the solutions. Explain why the mixture is not as hazadhous as the original solution from a waste disposal point of view.
It could be that each of the individual solutions neutralize on addition of water. The heat of reaction would be very high hence making the solution dangerous. After mixing and diluting with a large amount of running water, most of the heat would be dissipated.
Why is the buret rinsed with the sodium hydroxide solution prior to filling with solution?
NaOH ensures that all water or acid previously used in the buret is removed so you can have the correct balance.
the densty of air at 100 C is less than 1 gram is it reasonable to assume the vaporized liquid will forse all of the air out during heating?
No, it won't. The amount of air forced out will be equal to the amount of water vapor produced The amount does not increase with temperature past 100 degrees Celsius, so SOME of the air will be forced out, but not all.
A desiccant, or drying agent, is often added to aspirin in order to prolong the aspirin's shelf life by delaying hydrolysis. How can you easily determind if any aspirin has begun to hydrolize
Smell it, it will smell like vinegar. This is because when aspirin decomposes, acetic acid is formed, which is vinegar.
Is it necessary for the Erlenmeyer flask to be dry before pipeting the 25.00 mL sample of vinegar in it? Explain
The Flask doesnt have to be dry when the additional sample of vinegar sol are placed in the flask because the water present will not affect the quantity of acetic acid present
(b) Why would you not allow water to contact the foil cap while you are cooling the flask and vapor with running water
The Foil might retain some water and give a false or inaccurate result
Why must the vinegar sample be obtained in a dry beaker?
The beaker must be dry because any water present will dilute the vinegar sample.
Explain why you would expect thatΔH neutzn for HBr reacting with NaOH solution andΔhneutzn for HNO3 reacting with KOH solution would be identical. Write appropriate equations to support this explanation.
The net ionic equations for both the reactions aresame so they have identical ΔH neutralization
(a) How will you determine when the unknown liquid in the flask has completely vaporized?
The ring of liquid surrounding the boiling stone disappears as vaporization is complete
1.) Briefly explain why it is important to carry out this experiment in a well-ventilated area.
The unknown may be flammable, toxic and irritant
Briefly explain why it is important to stir the water in the hot water bath while you are determining the boiling point of a liquid.
The water is gonna heat up from the bottom up when you stir it, it lets the water heat up uniform.
Would the measured boiling point of your unknown liquid have been too high or too low if the thermometer bulb had rested on the bottom of the water-filled beaker? briefly explain.
Too high because it would be measuring the tempurature of the glass, not the water.
1.) Briefly describe the safety precautions that you must take working with flammable compounds.
Wear eye protection handle with care, no open flames
***A student following the procedure of this experiment obtained the following data for an unknown volatile liquid: mass of flask, boiling stone, foil cap and unknown after cooling 83.350 mass of flask, boiling stone, and foil cap, g 82.657 water bath temperature, °C 95.0 barometric pressure, in Hg 30.09 volume of flask, mL 270 accepted molar mass of unknown, g mol 86.2
a) mass of unknown 83.350-82.657= 0.693 g b)Temperature in K 95 + 273.15= 273.15 ? c)barometric pressure in atm 30.09/760= 0.0396 d)vol of the flask in liters 270/1000= 0.27 L e)density 0.693/0.27 = 2.57 f) MM of vaporized : g)percent error:
State what aqueous NaOH and KOH have incommom.
aqueous NaOH and KOH haveOH- ion in common.
Briefly explain why it was not necessary for you to determine the mass of unknown liquid that you transferred to the flask before heating.
because, as you heat this gas, you are creating sufficient vapor to drive out the air so to have the vapor of the liquid present,the test tube will contain only the vapor that you require to calculate the molar mass.
What hazards should you know about when you work with: 6M HCl used in part V of this experiment? ... ...
corrosive toxic and could burn
What hazards should you know about when you work with: (a) Your NaoH solution? ...
corrosive toxic and could burn
Calculate the heat transferred from the reaction of 50.0 mL of 1.00 M HNO_3 with 50.5 mL of 1.00 M NaOH solution. Assume the heat capacity of the mixture is 3.9 j g^-1 deg^-1
dH = - 103.5 grams(3.89J/g-C)(31.5 - 24.7C) dH = - 103.5 grams(3.89J/g-C)(6.8C) dH = - 2738 J
