Answers section
Questions 4.4.4 (b)
- State the observation made on the glass rod.
- Identify the substances that emerge from the bottles containing concentrated hydrochloric acid and concenrated ammonia solution respectively.
- Name the product formed when the two substances combine directly with each other.
- Write an equation to represent the direct combination reaction between the two fumes.
- From this experiment, suggest one method which may be used to identify ammonia gas, other than using red litmus paper.
Answers to Questions 4.4.4 (b) 
- Thick white fumes
- Hydrogen chloride gas; ammonia gas
- Ammonium chloride
- HCl(g) + NH3(g) → NH4Cl(s)
- Use of hydrogen chloride gas. White fumes indicate presence of ammonia gas.