Soft Drink Prac (1 Viewer)

[peony]

this prac is cool ! regarding the dot point-perform a 1st hand

investigation to decarbonate soft drink and gather data to

measure the mass changes involved and calculate the voulme of

the gas released at 25 C and 100kPa, we're told to list as many

errors as possible and suggest ways to improve

accuracy and i didn't came up with alot of ideas,

anyone could help...?

In addition, what are some aspects to talk about

under the point

discussion and what are the molar values for STP

and SLC now, i heard they have changed

 

[CHUDYMASTER]

Errors include:
-some of the soft drink might evaporate, hence making mass change reading incorrect.

-The weight reading will fluctuate since the ions and water molecules are excited and gradually cool off. This is so because the excited particles exert more force on the balance as they jump up and down

To improve accuracy, add a small amount of acid and note the mass of the acid beforehand. This will cause the emission of CO2 (refer to carbonate + acid equation)

Also...

STP (0 degrees celsius, 101.3 kPa) L/mol = 22.41
SLC (25 degrees celsius, 101.3 kPa) L/mol = 24.47

Even if they have changed, it will be given on the data sheet in the exam, so best just to stick with the value they give you.

 

[jims]

it was changed to the volume of an ideal gas at 100kPa:
at 0 = 22.71L
at 25 = 24.79L
should be on the 2003 data sheet

 

[The Bograt]

I came to this thread looking for this experiment. Exactly how do you perform the experiment, and measure the carbon dioxide accurately. My teacher asked us to think up how to do this experiment, and I really need some help!
Thanks in advance

 

[elizabethy]

a good description of this experiment is given in macquarie revision guide for chemistry....it has the errors n how 2 improve the prac as well
have a look if possible or i will post it up for u!!
thanx

 

[CHUDYMASTER]

There's no real strict experiment...

-Basically you measure the mass of the soft drink before and after opening it.

-The reaction is H2CO3 --> CO2 + H2O (the equilibrium shifts due to the reduction in pressure)

-Therefore, since CO2 is emitted as a gas, you can measure the reduction in mass as the mass of CO2.

-Knowing the mass of CO2, you can work out the moles of CO2, since n = m/M (M = 44 g/mol in this case)

-Then you may find the volume released using the formula V = 22.41 (or whatever the new value is for SLC)*moles of CO2

That should suffice.

 

[The Bograt]

elizabethy anything you could post from that revision guide would be great as I do not own it.
Thanks guys for everything posted so far

Is it fesible to add a catalyst and just wait for the CO2 to leave? how do you know that no more carbon dioxide is leaving the can?

 

[abdooooo!!!]

what is this... ahh im forgetting stuff. wait i have a something in my notes.

here:

2.3.1 Identify data, plan and perform a first hand investigation to decarbonate soft drink and gather data to measure the mass changes involved and calculate the volume of gas released at 25C and 100kPa.

Procedure:
A 390mL soft drink was bought
Weigh the soft drink (unopened)
Heated with electric hotplate to about 50C (open the soft drink)
Leave it standing for 2 hours
When cool, reweigh the can to determine the mass loss
Perform calculations

Calculations:
Loss of mass due to escape of carbon dioxide gas
Conversion of grams of CO2 lost to moles of CO2
Use of the knowledge that one mole of gas at 25oC and 100kPa occupies 24.8 L

Conclusion:
Carbon dioxide were lost
CO2(g) + H2O(l) H2CO3(aq) is exothermic
By using Le Chateliers principle:
o Heating pushes reaction to the left releases CO2
o Opening the lid reduces pressure pushes reaction to the left releases CO2

Accuracy and Reliability:
Water vapour is lost due to heating
o Control is set up: another bottle is filled with water equal volume to the soft drink and is heated together for same amount of time
o Mass difference between the bottles is the CO2

A means of weighing to at least the nearest gram with a electronic weighing scales for accuracy

Electric hot plate is used to provide a more even heating so to minimise the loss of water

Repetition and averaging the result would increase the accuracy and minimise experimental errors

Justification:
Buy unopened bottles with the liquid level as low as possible to avoid spilling

Electric hot plate is used because naked flame would burn the plastic bottle

 

[The Bograt]

I can't thank you guys enough!
Excellent work

 

[mushroom_head]

on one of my worksheets for this experiment said that a 375mL can of soft drink contains 1.4L of carbon dioxide. i don't understand how it can fit 1.4L when it's only a 375mL can...is it because of the pressure? That's what i thought it was all along.

 

[abdooooo!!!]

1.4 L of gas under what conditions? yes its because pressure.

gases can vary in terms of volumn depending on the pressure and temp... worksheet should of said it in terms of moles of gas.

 

[spice girl]

no, it's related to the pressure in the can because it's a closed system, but it's also because the CO2 is dissolved. remember that gases are particles that are very well spaced apart, but when dissolved, they are more close together

 

[t-i-m-m-y]

we drank it.

 

[t-i-m-m-y]

and yeah. use the one on the data sheet; good thing i used the data sheet in physics and chem, i memorised all the values of plancks constant etc

apparently it was changed around halfway thru the HSC 03 course

 

[peony]

Originally posted by The Bograt
I can't thank you guys enough!
Excellent work

i second that

 

[The Bograt]

My teacher said in 4 years that they have been doing the experiment only one kid got the exact answer (how much CO2 is in a can ok coke?) and it was some loser kid who was heaps bad in class. Teacher got angry at him cause he was doing nothing, so he said he could get the excact answer in 2 minutes.

He went and phoned the coke hotline on his mobile and they gave him the exact answer. What a genius