– Definition: The atomic mass unit (amu) is a unit used in chemistry to measure the mass of atoms and molecules on a relative scale.

– Relative Scale: Defined as 1/12th of the mass of a neutral carbon-12 atom; allows for easy comparison of masses.

– Approximate Value: 1 amu is roughly equal to the mass of a proton or a neutron, which is approximately 1.67 × 10^-27 kilograms.

– Comparative Use: Enables scientists to compare masses of different atoms and molecules conveniently.

– Representation in Periodic Table: Atomic masses of elements are commonly expressed in atomic mass units (amu).

– Example: For instance, the atomic mass of hydrogen is about 1.008 amu, indicating its mass relative to 1/12th of the mass of a carbon-12 atom.

– Importance: Essential in studying chemical reactions and understanding atomic structures by comparing and analyzing the masses of atoms and molecules.

Chemical Formula: A Concise Composition Notation
– Definition: A chemical formula is a symbolic representation illustrating the types and quantities of atoms present within a compound.

– Symbolic Representation: Utilizes elemental symbols (e.g., H for hydrogen, O for oxygen) and subscripts to denote the number of atoms in a compound.

– Types of Formulas:
– Molecular Formula: Specifies the actual count of atoms in a compound (e.g., H2O for water).
– Empirical Formula: Represents the simplest whole-number ratio of elements (e.g., CH2O for formaldehyde).

– Significance: Provides essential information about a compound’s composition, aiding in understanding its properties and behavior in chemical reactions. Serves as a standardized language in chemistry for communication and documentation.

To calculate the formula unit masses of compounds, we sum the atomic masses of the constituent atoms according to their respective formulas.

Given atomic masses:
– Zn = 65 u
– Na = 23 u
– K = 39 u
– C = 12 u
– O = 16 u

Formula Unit Mass Calculation:
1. ZnO (Zinc Oxide):
– Formula: ZnO
– Atomic mass of Zn = 65 u
– Atomic mass of O = 16 u
– Formula unit mass of ZnO = Atomic mass of Zn + Atomic mass of O
– Formula unit mass of ZnO = 65 u (Zn) + 16 u (O) = 81 u

2. Na₂O (Sodium Oxide):
– Formula: Na₂O
– Atomic mass of Na = 23 u
– Atomic mass of O = 16 u
– Formula unit mass of Na₂O = 2 × Atomic mass of Na + Atomic mass of O
– Formula unit mass of Na₂O = 2 × 23 u (Na) + 16 u (O) = 46 u + 16 u = 62 u

3. K₂CO₃ (Potassium Carbonate):
– Formula: K₂CO₃
– Atomic mass of K = 39 u
– Atomic mass of C = 12 u
– Atomic mass of O = 16 u
– Formula unit mass of K₂CO₃ = 2 × Atomic mass of K + Atomic mass of C + 3 × Atomic mass of O
– Formula unit mass of K₂CO₃ = 2 × 39 u (K) + 12 u (C) + 3 × 16 u (O) = 78 u + 12 u + 48 u = 138 u

Summary of Formula Unit Masses:
– ZnO (Zinc Oxide) = 81 u
– Na₂O (Sodium Oxide) = 62 u
– K₂CO₃ (Potassium Carbonate) = 138 u

Understanding Polyatomic Ions:
– Definition: Polyatomic ions are groups of atoms bonded together, carrying an electric charge. They act as a single charged unit in chemical reactions.

– Composition: These ions are made of two or more different types of atoms covalently bonded together.

– Charge: They have an overall electrical charge due to the gain or loss of electrons. This charge results from the combined effect of the atoms within the ion.

Importance and Behavior:
– Polyatomic ions play crucial roles in chemical compounds and reactions.
– They bond with other ions or atoms, forming molecules or ionic compounds with distinctive properties.
– Due to their unique structures and charges, polyatomic ions exhibit behavior distinct from individual atoms.

Conclusion:
Polyatomic ions are combinations of atoms that act as single charged units, influencing the properties and behavior of various chemical compounds. Their ability to bond with other elements forms the basis for many essential chemical reactions in nature and in the laboratory.

(a) Quick lime: The compound for quick lime is Calcium oxide (CaO). The elements present in quick lime are:
– Calcium (Ca)
– Oxygen (O)

(b) Hydrogen bromide: The compound for hydrogen bromide is Hydrobromic acid (HBr). The elements present in hydrogen bromide are:
– Hydrogen (H)
– Bromine (Br)

(c) Baking powder: Baking powder is a mixture that often contains compounds like sodium bicarbonate (NaHCO3) and an acid, such as cream of tartar (potassium hydrogen tartrate -KHC4H4O6). The elements present in baking powder can include:
– Sodium (Na)
– Hydrogen (H)
– Carbon (C)
– Oxygen (O)
– Potassium (K)
– Tartaric acid: Carbon (C), Hydrogen (H), Oxygen (O)

(d) Potassium sulphate: The compound for potassium sulphate is (K2SO4). The elements present in potassium sulphate are:
– Potassium (K)
– Sulfur (S)
– Oxygen (O)