There is Ch 18 Salts Solved Exercise for Class 10 Chemistry with the most important short questions. All notes for class 10 chemistry are here, and All Video lectures are here. Watch and Subscribe, please
A. Multiple Choice Questions
| Q. No. | Question Statement | Correct Answer |
|---|---|---|
| 1 | Which base is not soluble in water? | (b) Mg(OH)₂ |
| 2 | The shape of the crystal of NaCl is: | (a) Cubic |
| 3 | Which salts are always soluble in water? | (c) Nitrates |
| 4 | Which salt will be formed when marble pieces react with dilute nitric acid? | (b) Calcium nitrate |
| 5 | Water-insoluble salt is: | (a) Calcium sulphate |
B. Short Answer Questions (Salts Solved Exercise)
18.1. Which factors are responsible for the strength of electrostatic forces between ions?
The factors responsible for the strength of electrostatic forces between ions are:
- Charges on the ions: Higher charges on the ions lead to stronger electrostatic attractions.
- Sizes of the ions: Smaller ionic sizes allow the ions to come closer together, resulting in stronger electrostatic attractions.
18.2. Is lead (II) chloride soluble in water? Give comments.
No, lead (II) chloride (PbCl₂) is insoluble in cold water. According to the textbook’s solubility rules, while most chlorides are soluble, the chlorides of silver and lead are notable exceptions and remain insoluble in water.
18.3. Which lead salts are insoluble in water?
Based on the textbook rules, the following lead salts are insoluble in water:
- Lead (II) chloride (PbCl₂)
- Lead (II) sulphate (PbSO₄)
18.4. Name two insoluble carbonates.
All metallic carbonates are insoluble in water except those of sodium, potassium, and ammonium. Two examples of insoluble carbonates are:
- Calcium carbonate (CaCO₃)
- Magnesium carbonate (MgCO₃)
18.5. What is a crystal lattice?
A crystal lattice is a highly ordered, repeating three-dimensional arrangement of particles (atoms, molecules, or ions) in a crystalline solid. In an ionic crystal lattice like sodium chloride (NaCl), positive and negative ions are held firmly in fixed positions by strong electrostatic forces of attraction, forming a definitive geometrical shape.
C. Constructed Response Questions (Salts Solved Exercise)
18.1. Why are melting points of ionic salts generally very high?
Ionic salts exist as massive regular networks of alternating positive and negative ions held together by exceptionally strong electrostatic forces of attraction. To melt these solids, a tremendous amount of thermal energy is required to break these powerful forces and break down the rigid lattice structure, which is why their melting points are generally very high.
18.2. Why ionic salts exist in solid state?
Ionic salts exist in the solid state because the inter-particle electrostatic forces between the oppositely charged ions are extremely strong. These forces lock the ions into fixed, rigid positions within a crystal lattice. Because the ions lack translational motion and are restricted to vibrational movements about their mean positions, the substance retains a definite shape and volume, characterizing the solid state.
18.3. How will you prepare calcium sulphate in the laboratory?
Calcium sulphate (CaSO₄) is a water-insoluble salt. It is prepared in the laboratory by the method of precipitation (double displacement), which involves mixing solutions of two appropriate soluble salts:
Method: Mixing a solution of a soluble calcium salt (such as calcium chloride, CaCl₂) with a solution of a soluble sulphate salt (such as sodium sulphate, Na₂SO₄).
CaCl₂(aq) + Na₂SO₄(aq) → CaSO₄(s)↓ + 2NaCl(aq)
The insoluble calcium sulphate forms as a solid precipitate, which is then separated by filtration, washed with cold distilled water to remove impurities, and dried between the folds of filter paper.
18.4. Compare the melting points of NaCl and MgCl₂.
The melting point of Magnesium chloride (MgCl₂) is significantly higher than that of Sodium chloride (NaCl). This difference is due to the following reasons:
- Ionic Charge: The magnesium ion (Mg²⁺) carries a higher positive charge (+2) compared to the sodium ion (Na⁺, +1).
- Ionic Size: The Mg²⁺ ion has a smaller ionic radius than the Na⁺ ion.
According to the textbook, higher charges and smaller ion sizes lead to stronger electrostatic attractions within the crystal lattice. Because the lattice energy of MgCl₂ is much greater, it requires more energy to disrupt, leading to a higher melting point.
18.5. How would you prepare pure crystals of copper sulfate in the laboratory?
Copper sulfate (CuSO₄) is a water-soluble salt. It is prepared in the laboratory via a neutralization reaction between a soluble acid and an insoluble base (Copper(II) oxide or Copper(II) carbonate):
Procedure:
- Take a measured volume of dilute sulphuric acid (H₂SO₄) in a beaker and warm it gently.
- Add small amounts of copper(II) oxide (CuO) powder slowly into the warm acid with constant stirring. Continuous addition ensures that the base is in excess and all the acid is completely neutralized.
- Filter the hot reaction mixture to remove the excess, unreacted copper(II) oxide powder. The clear blue filtrate collected contains dissolved copper sulfate.
- Transfer the filtrate into an evaporating dish and heat it gently to concentrate the solution until a thin film of crystals starts forming on the surface (the crystallization point).
- Allow the hot, saturated solution to cool down slowly. Pure blue crystals of copper sulfate will start appearing.
- Filter the mixture to isolate the pure copper sulfate crystals, wash them with a tiny amount of cold distilled water, and dry them safely between the folds of filter paper.
