WAEC Chemistry practical: Identify the substances present in sample C based on the given tests and observations.

Here are the observations and inferences for the WAEC Chemistry practical question:

a) Test: Put about half a spatula of C in a boiling tube and heat strongly. Allow it to cool.

• Observation: The sample chars, a colorless liquid condenses at the cooler part of the test tube, and a gas is evolved which turns lime water milky.
• Inference: Presence of an organic compound (chars), water of crystallization or constitution (colorless liquid), and a carbonate or oxalate (gas turns lime water milky, indicating carbon dioxide, $\text{CO}_2$).

b) i) Test: To the remaining portion of C, add about $2 \text{ cm}^3$ of dilute trioxonitrate (V) acid, $\text{HNO}_3$. Stir well to dissolve and filter, keep both the filtrate and the residue.

• Observation: Effervescence occurs, a colorless, odorless gas is evolved which turns lime water milky. Part of the sample dissolves, leaving a white residue.
• Inference: Presence of carbonate ($\text{CO}_3^{2-}$). The gas evolved is carbon dioxide ($\text{CO}_2$). The sample contains both soluble and insoluble components.

b) ii) Test: To the residue, add a few drops of iodine solution.

• Observation: The white residue turns blue-black.
• Inference: Presence of starch.

c) i) Test: To the first portion of the filtrate obtained in (b)(i), add Sodium Hydroxide Solution ($\text{NaOH}$) in drops and then in excess.

• Observation:
  • In drops: A dirty green precipitate is formed.
  • In excess: The dirty green precipitate is insoluble in excess $\text{NaOH}$.
• Inference: Presence of iron(II) ions ($\text{Fe}^{2+}$).

c) ii) Test: To the second portion of the filtrate obtained in (b)(i), add aqueous $\text{NH}_3$ in drops and then in excess.

• Observation:
  • In drops: A dirty green precipitate is formed.
  • In excess: The dirty green precipitate is insoluble in excess $\text{NH}_3$.
• Inference: Presence of iron(II) ions ($\text{Fe}^{2+}$) confirmed.