Chapter 5, Problem 1RQ

a.

Interpretation Introduction

Interpretation:

A formula unit should be explained.

Concept Introduction:

A crystal lattice of an ionic compound is composed of many cations and anions; thus, the concept of Formula unit has been introduced to indicate the lowest whole number ratio of the cations and the anions, which represents the whole crystal lattice. It has the same composition and the same physical and chemical properties as of the whole crystal lattice.

For a covalent compound, it is same as the formula of the molecule of the compound.

Answer to Problem 1RQ

Solution:

A formula unit indicates the lowest whole number ratio of ions in an ionic compound or atoms of elements in a covalent compound.

Explanation of Solution

A crystal lattice is formed by several ions both the anions and the cations, the formula of the compound with the number of each element, cannot be determined. Thus, the concept of Formula mass is introduced. Formula mass is the smallest possible ratio of the elements present in an ionic compound.

For a covalent compound, it is same as the formula of the molecule of the compound.

The formula unit has the same properties as of the compound and it is the smallest particle that can take part in any chemical reaction.

b.

Interpretation Introduction

Interpretation:

The formula mass should be explained.

Concept Introduction:

The formula mass of a compound is the mass of the molecule of the compound formed. It is calculated by summing up the atomic weights of all the elements present in the molecule of that compound. The unit of formula mass is amu (Atomic Mass unit).

Answer to Problem 1RQ

Solution:

The formula mass of a compound is the mass of the molecule of the compound formed. It is calculated by summing up the atomic weights of all the elements present in the molecule of that compound. The unit of formula mass is amu (Atomic Mass unit).

Explanation of Solution

For covalent substances, the formula represents the type of atoms covalently bonded to each other to form a molecule and the sum of atomic masses is known as molecular mass or formula mass of the compound.

For example, formula mass of water is 18 amu

Ionic compounds are neutral compounds formed by the cations and anions that are combined in fixed ratio.

For example, the formula mass of Sodium chloride is 58.44 amu.

c.

Interpretation Introduction

Interpretation:

A mole should be explained.

Concept Introduction:

1 mole of any substance contains 6.022×10²³ particles in it. The particles can be atoms, molecules or ions.

Like for 12 we call a dozen
For a Quantity of 6.022×10²³, we call it a mole.

This is concluded from Avogadro’s law hence it is also called as Avogadro’s number. It is denoted by symbol $N_A$ .

The carbon, C-12 atom was taken as reference and 1 mole is defined as the number of atoms present in 12 g of C-12 atom.

Answer to Problem 1RQ

Solution:

A mole is defined as the amount of substance containing the same number of particles (such as atoms, molecules, and ions) as the number of atoms in a sample of pure 12 C weighing exactly 12 g.

Explanation of Solution

A mole is defined as the amount of substance containing the same number of particles (such as atoms, molecules, and ions) as the number of atoms in a sample of pure 12C weighing exactly 12 g.

1 mole of any element contains the same number of atoms as 1 mole of any other element. The masses of 1 mole of different elements, however, are different. The molar mass of an element (or compound) is the mass in grams of 1 mole of that substance, a property expressed in units of grams per mole (g/mol).

d.

Interpretation Introduction

Interpretation:

Avogadro's number should be explained.

Concept Introduction:

Avogadro’s number is a magnitude or a quantity that denotes the number of units in 1 mol of the substance. In chemistry we use Avogadro’s number for the number of particles present that can be atoms, molecules or ions in 1 mol of a substance

1 mole of any substance contains 6.022×10²³ units of particles in it.

Answer to Problem 1RQ

Solution:

Avogadro’s number is 6.022×10²³mol-1 this is number of units of a substance present in 1 mole.

Explanation of Solution

The magnitude of the Avogadro’s number is 6.022×10²³, it is the number of units that can be atoms, ions or molecules in 1 mol of a substance. It is expressed as the symbol N_A.

Like for 12 we call a dozen

For a Quantity of 6.022×10²³, we call it a mole.

Thus, 1 mole of any substance contains 6.022×10²³ units of that substance.

e.

Interpretation Introduction

Interpretation:

The molar mass should be explained.

Concept Introduction:

The molar mass of a compound is calculated by taking sum of atomic masses of atoms present in it. The unit of molar mass is g/mol.

Answer to Problem 1RQ

Solution:

Molar mass as the name tells, is the mass of 1 mole of any substance i.e. an element, a compound or an ion. The unit of molar mass is gram per mole.

Explanation of Solution

Molar mass as the name tells, is the mass of 1 mole of any substance i.e. an element, a compound or an ion. The unit of molar mass is gram per mole. Molar mass can be calculated by adding the atomic masses of all the atoms present in a Chemical compound. For a mole of ions, the molar mass is same as that of the parent atom, since the mass of the electron is very less and can be neglected.

Molar mass of water is 18 g/mol.

Molar mass of Hydrochloric acid is 36.5 g/mol.

f.

Interpretation Introduction

Interpretation:

Molar volume should be explained.

Concept Introduction: As the name suggests the molar volume is the volume of any substance having particles equal to Avogadro’s number or 6.022×10²³ particles. It is represented by $V_m$ . The formula for calculating molar volume is-

  $V_m=\frac{V}{n}$

At a given temperature and pressure value, 1 mole of any gas has a fixed volume. This is known as molar volume of the gas.

Answer to Problem 1RQ

Solution:

Volume of 1 mol of a substance.

Explanation of Solution

The molar volume is defined as the volume of 1 mole of substance.  It can be calculated by taking ratio of volume of a sample by its number of moles as follows:

  $V_m=\frac{V}{n}$

Thus, $V_m$ is the volume occupied by one mole of a substance
One mole of any gas at a temperature and pressure has fixed volume and known as its Molar gas volume.