Inorganic Chemistry 1 — Questions and Answers
Question 1: Which of the following is the oxidation state of chromium in potassium dichromate (K2Cr2O7)?
- +2
- +3
- +6 (Correct answer)
- +7
Correct answer: +6
In potassium dichromate (K2Cr2O7), potassium (K) has an oxidation state of +1, and oxygen (O) typically has an oxidation state of -2. To find the oxidation state of chromium (Cr), we set up the equation: 2(+1) + 2(Cr) + 7(-2) = 0. Solving this gives 2 + 2Cr - 14 = 0, which simplifies to 2Cr = 12, so Cr = +6.
Question 2: What is the geometry of the ammonia (NH3) molecule according to the VSEPR theory?
- Linear
- Trigonal planar
- Trigonal pyramidal (Correct answer)
- Tetrahedral
Correct answer: Trigonal pyramidal
According to VSEPR theory, the geometry of a molecule is determined by the repulsion between electron domains around the central atom. In ammonia (NH3), the central nitrogen atom has three bonding pairs with hydrogen atoms and one lone pair of electrons. These four electron domains arrange themselves in a tetrahedral electron geometry, but the lone pair exerts greater repulsion, distorting the molecular geometry into a trigonal pyramidal shape.
Question 3: Which compound is known as quicklime?
- Calcium carbonate
- Calcium oxide (Correct answer)
- Calcium hydroxide
- Calcium chloride
Correct answer: Calcium oxide
Quicklime is the common name for calcium oxide (CaO). It is a white, caustic, alkaline crystalline solid at room temperature. Calcium oxide is produced by the thermal decomposition of materials like limestone (calcium carbonate, CaCO3) in a process called calcination, and it is widely used in various industrial applications.
Question 4: Which of the following elements is a transition metal?
- Sulfur
- Iron (Correct answer)
- Sodium
- Phosphorus
Correct answer: Iron
Transition metals are elements that have partially filled d-orbitals in their atoms or form ions with partially filled d-orbitals. They are located in groups 3-12 of the periodic table. Iron (Fe) is found in Group 8 and Period 4, possessing characteristic properties of transition metals such as variable oxidation states and the formation of colored compounds.
Question 5: What type of bond exists in sodium chloride (NaCl)?
- Covalent bond
- Ionic bond (Correct answer)
- Metallic bond
- Hydrogen bond
Correct answer: Ionic bond
An ionic bond forms between a metal and a non-metal due to the complete transfer of electrons, creating oppositely charged ions that are electrostatically attracted. In sodium chloride (NaCl), sodium (a metal) donates an electron to chlorine (a non-metal), forming a positively charged sodium ion (Na+) and a negatively charged chloride ion (Cl-). The strong electrostatic attraction between these ions constitutes the ionic bond.
Question 6: Which gas is evolved when zinc reacts with dilute hydrochloric acid?
- Oxygen
- Nitrogen
- Hydrogen (Correct answer)
- Carbon dioxide
Correct answer: Hydrogen
When an active metal like zinc reacts with a dilute acid such as hydrochloric acid, a single displacement reaction occurs. The zinc displaces the hydrogen from the acid, forming a salt (zinc chloride) and releasing hydrogen gas. The balanced chemical equation for this reaction is Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g).
Inorganic Chemistry 1
Which of the following is the oxidation state of chromium in potassium dichromate (K2Cr2O7)?