Question

When an ionic compound such as sodium chloride (NaCl) is placed in water, the component atoms of the NaCl crystal dissociate into individual sodium ions (Na+) and chloride ions (Cl-). In contrast, the atoms of covalently bonded molecules (e.g., glucose, sucrose, glycerol) do not generally dissociate when placed in aqueous solution. Which of the following solutions would be expected to contain the greatest number of solute particles (molecules or ions)?
A) 1 L of 1.0 M NaCl
B) 1 L of 0.5 M NaCl
C) 1 L of 0.5 M glucose
D) 1 L of 1.0 M glucose
E) C and D will contain equal numbers of particles.

Answer 1

Answer:

• The solution expected to contain the greatest number of solute particles is: A) 1 L of 1.0 M NaCl

Explanation:

The number of particles is calculated as:

a) For Ionic compounds:

• molarity × volume in liters × number of ions per unit formula.

b) For covalent compounds:

• molarity × volume in liters

The difference is a factor which is the number of particles resulting from the dissociation or ionization of one mole of the ionic compound.

So, calling M the molarity, you can write:

• # of particles = M × liters × factor

This table show the calculations for the four solutions from the list of choices:

Compound    kind         Particles in solution  Molarity   # of particles

                                       (dissociation)              (M)          in 1 liter

A) NaCl          ionic            ions Na⁺ and Cl⁻        1.0            1.0 × 1 × 2 = 2

B) NaCl          ionic            ions Na⁺ anc Cl⁻        0.5           0.5 × 1 × 2 = 1

C) Glucose    covalent     molecules                   0.5          0.5 × 1 × 1 = 0.5

D) Glucose    covalent     molecules                   1.0           1.0 × 1  × 1 = 1

Therefore, the rank in increasing number of particles is for the list of solutions given is: C < B = D < A, which means that the solution expected to contain the greatest number of solute particles is the solution A) 1 L of 1.0 M NaCl.