Inorganic QA

Inorganic QA

Inorganic QA is one of the most feared components besides planning question for H2 Chemistry practical.

QA inorganic chemistry

Here’s a useful framework you can use to approach this part of the practical assessment.

  1. Preliminary observations: Begin by making preliminary observations of the sample, such as color, odor, and physical state. These observations can provide initial clues about the composition of the sample.
  2. Group separation: In inorganic QA, ions are often grouped based on their solubility properties. The sample is typically divided into different fractions by adding specific reagents (eg adding NaOH or ammonia to test for metal cations) to selectively precipitate or dissolve certain groups of ions. This step helps to simplify the analysis process.
  3. Confirmatory tests: Once the ions are separated into different groups, you can perform specific confirmatory tests to identify the presence or absence of particular ions within each group. These tests typically involve the addition of reagents that produce characteristic color changes, precipitates, or gas evolution reactions. For example, if you are told there is certain anions in the group, you can add silver nitrate to test for halide ions, or barium chloride to test for sulfate ions etc. Take care NOT to add sulfuric acid then test for sulfate ions (i.e. don’t add reagents with the ions you are testing for!)
  4. Observations and data analysis: Record your observations carefully during the confirmatory tests. Note any color changes, precipitate formations, gas evolution, or other reactions that occur. Compare your observations with known reactions and expected results to draw conclusions about the presence or absence of specific ions. Usually you need to have an idea what type of reaction has probably happened, e.g. if you add KI and you see a brownish suspension, a redox reaction likely occurred. The brown solution formed is likely iodine with a white precipitate of copper iodide. You should let the suspension settle for 5 mins so that you can see a brown solution and white precipitate at the bottom of the test-tube. Deduction: copper 2+ ion present.
  5. Systematic analysis: Follow a systematic approach to analyze each group of ions individually. Perform confirmatory tests for each group, taking into account any observations or results obtained in the earlier steps. Continue narrowing down the possibilities until you have identified all the ions in the sample. Use precipitation to separate cations into filtrate and reside then conduct addition test. Eg. adding ammonia to copper ions will produce blue precipitate, then adding excess will cause the blue precipitate to dissolve into deep blue solution, adding acid dropwise will reform the blue precipitate.
  6. Verification and cross-checking: After completing the analysis, it is essential to verify the results and cross-check them to ensure accuracy. Review your observations, data, and conclusions to confirm that they are consistent and logical. Look for any inconsistencies or errors that may have occurred during the analysis process. (see point 3 above)

Hope this framework has been helpful to your revision!

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