The effect of dissolved carbon dioxide on the pH of water (2 Viewers)

[princesscal]

We're doing a prac for our first assessment task and it's worth 20%. It's on the syllabus point 2.3.1 - Perform a first hand investigation to demonstrate the effect of dissolved carbon dioxide on the pH of water.

To make the CO2 we need to add HCl to Marble Chips (CaCO3), I need to know how we can collect the gas after making it and perform the actual experiment. I am having trouble with this for some obscure reason.

 

[xiao1985]

An easier way to make CO2: exhale.

use a straw and blow into a water solution containing universal indicator and observe colour change.

 

[white ferret]

An easier way to make CO2: exhale.

use a straw and blow into a water solution containing universal indicator and observe colour change.

no offence, but that's a really bad way to do it coz it doesnt prove that it's the CO2 that's causing the change in acidity.

We're doing a prac for our first assessment task and it's worth 20%. It's on the syllabus point 2.3.1 - Perform a first hand investigation to demonstrate the effect of dissolved carbon dioxide on the pH of water.

To make the CO2 we need to add HCl to Marble Chips (CaCO3), I need to know how we can collect the gas after making it and perform the actual experiment. I am having trouble with this for some obscure reason.

ull need 2 test tubes, a delivery tube with a rubber/cork stopper, which should all b supplied aniwayz.. add the acid + marble to one test tube, then use the stopper to make sure that all the CO2 created goes into the delivery tube which feeds into the 2nd test tube containing distilled water + universal indicator. u should then b able to observe the colour change.

[sorry if that was confusing.. look at the equipment.. that might helppp]

 

[Adamman]

We just did this experiment not too long ago.

Firstly, we did it as xiao1985 suggested.

First of all, do a investigation to back up the claim that we do indeed exhale CO2; blow through a straw into a beaker of Limewater, if it turns cloudy, which it will, this will prove we produce CO2.

From there place 100ml of water in a beaker, and place some universal indicator in the beaker, this will be your control. You should get a colour which matches a pH level of about 7.5.
Then get another beaker with 100ml of water, place the universal indicator in it, but blow into the beaker with a straw for 1 minute, the colour will change to a yellow/orange meaning it has turned slightly acidic.
A chemical reactions has also taken place:
CO2 + H2O == H2CO3 [Carbonic Acid]

Carbonic Acid is a chemical which is not wanted in the body, hence why we exhale it; our body wants to get rid of it as quickly as possible.

 

[katie_tully]

yeah thats all we did
we exhaled into a straw into a beaker of water and watched the pH change

no offence, but what else in exhaled air would be causing the pH change

 

[Reirax Gnow]

actually, the prac i did was also blowing CO2 into water. So what? The experiment doesnt necessary to be successful in order to get high mark! This method provides a lot of things to be discussed(such as why isnt the results valid) and gives us opportunities to show the marker our understanding in what we are doing.

 

[xiao1985]

well... to be honest, if one is to conduct a vigorous test of the effect of CO2 on pH of the water, not only does one have to use AR grade CaCO3, AAS grade nitric acid, but also a pH meter that can detect up to 3 sig fig.

I admit blowing exhaled air is abit crude, but at times, compromise needs to be made...

also this method gives you one more thing to write about in terms of safety (don't suck)

 

[katie_tully]

well... to be honest, if one is to conduct a vigorous test of the effect of CO2 on pH of the water, not only does one have to use AR grade CaCO3, AAS grade nitric acid, but also a pH meter that can detect up to 3 sig fig.

I admit blowing exhaled air is abit crude, but at times, compromise needs to be made...

also this method gives you one more thing to write about in terms of safety (don't suck)

HSC biology doesnt need to be that indepth though anyway. It's assumed knowledge that blowing into a straw will produce CO2 and a change in pH. Even if you did a more complex and accurate test the results are going to be the same.

Bludge your way through the HSC man, seriously.

 

[xiao1985]

shhh,

i'm making my defence here! =)

 

[katie_tully]

sorry