pH of CO2.... practical (1 Viewer)

[currysauce]

anyone got any info on this prac... i just want some background knowlegde....

thanks!

 

[meLoncoLLie]

Study guides/your teacher/notes from past HSCers/CSU HSC Online website

 

[*sarah*]

Which prac is that? The one where you blow air into water and measure the ph change?

 

[Danoz The Great]

Basically, dissolved CO2 in water lowers the pH of it. I think that's all you really need to know.

I think the pH went from 7 - 3ish.

 

[lukebennett]

http//:hsc.csu.edu.au/biology/core/balance/9_2_2/922net.html

 

[xiao1985]

if u need eqn:

co2 + h2o <---> h2co3
carbon dioxide + water <-------> carbonic acid

 

[currysauce]

any info on variables or have i got it right?

indep. varibl. is the addition C02
dep. varbl. is the pH change correct

would a control be, doing one without any C02 addition, thus effectively showing that it is the C02 that is causing the pH change?

 

[lukebennett]

any info on variables or have i got it right?

indep. varibl. is the addition C02
dep. varbl. is the pH change correct

would a control be, doing one without any C02 addition, thus effectively showing that it is the C02 that is causing the pH change?

ie another cup of water with a pH of about 7 or neutral. i dont think you need one though because you can see what the water began as and ends as. you are looking just for the effect on ph=decreased pH

 

[currysauce]

well u need a control....well we need one

 

[acmilan]

If you are doing the one by blowing in the water the control can just be a beaker of water that you dont blow air into, proving its pH will remain at 7. Technically you should perform a procedure to prove that your breath actually contains carbon dioxide, this can be done by blowing into lime water, that will make it go foggy.

Alternate method that can be used is to mix hydrochloric acid with calcium pebbles. This forms CO2 gas that can be trapped using an elbow in the flask and directed straight into a beaker of distilled water

 

[lukebennett]

If you are doing the one by blowing in the water the control can just be a beaker of water that you dont blow air into, proving its pH will remain at 7. Technically you should perform a procedure to prove that your breath actually contains carbon dioxide, this can be done by blowing into lime water, that will make it go foggy.

Alternate method that can be used is to mix hydrochloric acid with calcium pebbles. This forms CO2 gas that can be trapped using an elbow in the flask and directed straight into a beaker of distilled water

it is performed with the knowledge that the air we breath out contains CO2.

 

[acmilan]

I know but you cant make assumptions when performing experiments, if that was the case you wouldnt need controls as it is obvious that nothing will occur to the control water

 

[lukebennett]

i know what you mean but i dont think it really matters for this experiment. it is such a basic fact that we expell CO2 from our lungs that it doesnt need any testing. its not in the aim or anything either. a simple control is the pH of the water before you blow into it also. the lungs are simply the source of the CO2. its like when we have bottles of HCl-we dont test to make sure its HCl. i think ill stop arguing now lol. getting a bit silly. test it for CO2 if you like. did your teacher make you do that?

 

[acmilan]

Well not really we did the HCl and calcium pebbles one but he did a quick demonstration of the blowing into air one and someone happened to ask the question of how can we be certain that we are expelling CO2 so he pulled out the lime water

 

[lukebennett]

we asked ours and he said as long as it is CO2 it was fine. we didnt test it but the person who asked was either dumb or trying to be stupid for fun lol

 

[currysauce]

ok ... lol stop arguing... i haven't go teh method......

but say its the blowing one... the control would be one without blowing.... at least that says its our breath chanign the pH.....

but since we have to dicuss modifications... i would say limewater... with the justification that, our breath contains Co2... for starters... the fact that it might not be just c02 we are exhaling... other factors (i.e our breath vapor may have its own pH)... etc...

nice i got a lot to talk about!

 

[xiao1985]

if u really need a control, stir a soln vigorously, or use a pump to pump normal air into the soln...

just as a side fact, with atmospheric conc of co2, water's ph can be as low as 4 or so...
lolz, once we poured some universal indicator into the distilled water, and it turned pink...

 

[jamesy_1988]

anyone got any info on this prac... i just want some background knowlegde....

thanks!

if you need any info on the prac email me at jamesy_1988@hotmail.com because i have just done mine.

If you want to have a look at the results go to www.geocities.com/jamesyscience/1.bmp

Make sure that you save the picyure that way the graphics will turn out better

Jamesy