Identify the gas, write the equations of the reactions, and suggest one more test to identify the acid radical present.

$$
\text{Cr}_2\text{O}_7^{2-}(\text{aq}) + 3\text{SO}_2(\text{g}) + 2\text{H}^{+}(\text{aq}) \rightarrow 2\text{Cr}^{3+}(\text{aq}) + 3\text{SO}_4^{2-}(\text{aq}) + \text{H}_2\text{O}(\text{l})
$$
(Orange dichromate is reduced to green chromium(III) ions).

• One more test to identify the acid radical (Sulfite, $\text{SO}_3^{2-}$): Add a few drops of acidified potassium permanganate ($\text{KMnO}_4$) solution to the solution containing the sulfite radical. The purple color of the permanganate solution will be decolorized as the sulfite is oxidized to sulfate. $$2\text{MnO}_4^{-}(\text{aq}) + 5\text{SO}_3^{2-}(\text{aq}) + 6\text{H}^{+}(\text{aq}) \rightarrow 2\text{Mn}^{2+}(\text{aq}) + 5\text{SO}_4^{2-}(\text{aq}) + 3\text{H}_2\text{O}(\text{l})$$

4. a) What are the physical properties of chlorides? b) Give the equation for the reaction between 0.1M NaCl and con.HSO. c) Write short notes on how to recognize the product above.

• a) Physical properties of chlorides:

  • Most chlorides are white crystalline solids.
  • The majority are soluble in water, with notable exceptions like silver chloride ($\text{AgCl}$), lead(II) chloride ($\text{PbCl}_2$), and mercury(I) chloride ($\text{Hg}_2\text{Cl}_2$).
  • They generally have high melting and boiling points due to their ionic nature.
  • Some transition metal chlorides can be colored (e.g., copper(II) chloride is blue-green).

• b) Equation for the reaction between 0.1M NaCl and con.HSO: Assuming "con.HSO" refers to concentrated sulfuric acid ($\text{H}_2\text{SO}_4$):

  $$\text{NaCl}(\text{s}) + \text{H}_2\text{SO}_4(\text{conc}) \xrightarrow{\text{heat}} \text{NaHSO}_4(\text{s}) + \text{HCl}(\text{g})$$

• c) How to recognize the product above (HCl gas):

  • Dense white fumes with ammonia: Bring a glass rod dipped in concentrated ammonia solution near the gas. Dense white fumes of ammonium chloride will be observed.
  $$\text{HCl}(\text{g}) + \text{NH}_3(\text{g}) \rightarrow \text{NH}_4\text{Cl}(\text{s})$$
  • Litmus paper test: The gas turns blue litmus paper red, indicating its acidic nature.
  • Silver nitrate test: When passed through silver nitrate solution, it forms a white precipitate of silver chloride, which is insoluble in nitric acid but soluble in ammonium hydroxide.
  $$\text{HCl}(\text{g}) + \text{AgNO}_3(\text{aq}) \rightarrow \text{AgCl}(\text{s}) + \text{HNO}_3(\text{aq})$$

5. a) Give the physical properties of borates. b) Describe Tumeric paper test for the identification of borates. c) Write equation for the reaction between borate and barium chloride.

• a) Physical properties of borates:

  • Most borates are white crystalline solids.
  • Many are sparingly soluble or insoluble in water, though sodium borate (borax) is soluble.
  • They often exist as hydrates (containing water of crystallization).
  • They are generally stable compounds.

• b) Turmeric paper test for the identification of borates:

The turmeric paper will turn a distinct reddish-brown color.

The color will change to greenish-black.

• c) Equation for the reaction between borate and barium chloride: Assuming a simple borate like sodium metaborate ($\text{NaBO}_2$): $$2\text{NaBO}_2(\text{aq}) + \text{BaCl}_2(\text{aq}) \rightarrow \text{Ba(BO}_2)_2(\text{s}) + 2\text{NaCl}(\text{aq})$$ A white precipitate of barium metaborate is formed.