Coursework - unknown acid: tests - PLEASE HELP

In summary, the conversation discusses the need for help with a Chemistry coursework involving the identification of an unknown aqueous substance as an acid. The two chemical tests suggested are CO2 emission in limewater and H emission from acid + metal. The process for the CO2 test involves heating the substance to produce carbon dioxide and directing it into limewater, which will turn cloudy due to the reaction between CO2 and Ca(OH)2. The second test involves dropping a piece of metal into the unknown liquid and observing for bubbles, indicating the presence of hydrogen gas. However, it is mentioned that the unknown substance may not necessarily be an acid and there may be better tests for determining its cation.
  • #1
thick1
1
0
coursework - unknown acid: tests - PLEASE HELP!

can someone PLEASE help me?!

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 don't know how you actually DO these tests...or anything about the H+ ions which cause the gas emissions.

PLEASE PLEASE PLEASE can someone help me out?

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).
 
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  • #2
thick1 said:
1. Test is CO_2 emission in Limewater.
Simply heat whatever produces the carbond dioxide and then 'direct' the carbon dioxide into the limewater. The linewater will then turn cloudy because:

[tex]CO_2_{(g)} + Ca(OH)_2_{(l)} \rightarrow CaCO_3_{(s)} + H_2O_{(l)}[/tex]

Simple as that.

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

The Bob (2004 ©)
 
  • #3
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.
 
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1. How do I prepare for the unknown acid coursework?

To prepare for the unknown acid coursework, it is important to review the principles and techniques of acid-base titration and pH measurement. Familiarize yourself with the equipment and chemicals that will be used, and practice carrying out titrations and recording accurate measurements. Additionally, make sure to carefully read and understand the instructions and guidelines for the specific tests that will be performed on the unknown acid.

2. What are the safety precautions for testing unknown acids?

When working with unknown acids, it is crucial to take safety precautions to avoid any accidents or exposure to harmful chemicals. Wear appropriate personal protective equipment, such as gloves and goggles, and make sure to work in a well-ventilated area. Follow proper handling and disposal procedures for the chemicals used, and always wash your hands thoroughly after handling any substances.

3. How do I identify the unknown acid using titration?

To identify the unknown acid using titration, you will need to perform an acid-base titration using a known concentration of base (such as sodium hydroxide) and a suitable indicator (such as phenolphthalein). The volume of base required to neutralize the acid will allow you to calculate the concentration of the unknown acid using the equation M1V1 = M2V2. You can then determine the identity of the acid by comparing its concentration to known values for different acids.

4. What other tests can be performed on the unknown acid?

In addition to titration, you can perform other tests on the unknown acid to gather more information about its properties. For example, you can measure the pH of the solution using a pH meter or indicator paper, or conduct a flame test to observe the color of the flame when the acid is heated. You can also use conductivity measurements or qualitative analysis techniques to determine the presence of specific ions in the solution.

5. What factors can affect the accuracy of the results for the unknown acid tests?

There are several factors that can impact the accuracy of the results for the unknown acid tests. These include human errors, such as incorrect measurement or recording of data, as well as environmental factors like temperature and humidity. Contamination of equipment or chemicals can also affect the results, so it is important to properly clean and handle all materials. It is also essential to follow all instructions and perform the tests carefully and precisely to obtain accurate results.

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