1. Jan 6, 2005

thick1

as my username suggests...i am thick when it comes to Chemistry....so i really need some help with my coursework.

basically i need to know the 2 chemical tests (without use of indicators) to test an unknown aqueous substance to see if it is an acid.

1 test is CO2 emission in Limewater.
2 test is H emission from acid + metal.

thing is...i dont know how you actually DO these tests....or anything about the H+ ions which cause the gas emissions.

i need to know about the donating and receiving of H+ ions AND the apparatus needed and the methods of both the 2 tests.

Sorry...should have said...the unknown acid formula is MHSO4 (where M is either sodium or potassium).

2. Jan 6, 2005

The Bob

Simply heat whatever produces the carbond dioxide and then 'direct' the carbon dioxide into the limewater. The linewater will then turn cloudy because:

$$CO_2_{(g)} + Ca(OH)_2_{(l)} \rightarrow CaCO_3_{(s)} + H_2O_{(l)}$$

Simple as that.

Search for a website and you should find the set up and the equation.

3. Jan 6, 2005

Gokul43201

Staff Emeritus
I don't see how the CO2 test in limewater help identify if an unknown liquid is an acid. What role does the unknown liquid play in this experiment ? Anyway, the reaction is what The Bob has described above and the carbonate (CaCO3) will form a milky white dispersion. This can be done by simply blowing the CO2 into the liquid using a transfer tube. In fact, as your breath has some CO2 in it, you can simply blow through a straw suberged in limewater to see it turn milky.

The second test makes sense. Take a fresh piece of metal, one without any oxide layer - preferably in the form or wire, wool, filings or ribbon, so as to provide a large surface area. Zinc ribbon or well-cleaned copper wire will do. Drop it into the unknown liquid and look for bubbles rising up from the piece of metal.

Establishing that the gas evolved is really hydrogen is a little harder and I don't know if that's required at your level.

Edit : Just noticed your last line which says that the unknown is (Na/K)HSO4. These are bisulphates, and though they contribute H+ ions, they are not strictly considered acids. Now I can definitely think of better tests to determine the unknown cation, but I'm not sure now, what exactly you're trying to identify - the unknown cation, or the acidity of the liquid.

Last edited: Jan 6, 2005