☰ Contents · Chemistry (General chemistry)

Relations between percent, molar and normal concentration

Lessons 20–21 · 2 lessons · S. Masharipov, A. Mutalibov, E. Murodov, H. Islomova. General chemistry, Grade 11, 1st edition. G‘afur G‘ulom Publishing and Printing House, Tashkent, 2018
21

Relation between percent and normal concentration

Textbook: pp. 94–97
GoalApply the conversion formulas between percent and normal concentration (C_N = C%·ρ·10/E) and find the equivalent mass.
New words
normal concentration · normal konsentratsiyaequivalent mass · ekvivalent massaconversion formula · o‘tish formulasidensity · zichlik
Explanation

The relation between percent and normal concentration is similar to that between percent and molar concentration, except that the equivalent mass E replaces the molar mass M: C_N = C%·ρ·10/E, and conversely C% = C_N·E/(ρ·10). They give the density ρ = C_N·E/(C%·10) and the equivalent mass E = C%·10·ρ/C_N; once E is found an unknown substance can be identified. Between molar and normal concentration C_N = z·C_M (z is the number of exchangeable H⁺, OH⁻ or metal charges per formula unit). For example for 36.5 % HCl (ρ = 1.2 g/mL, E = 36.5) C_N = 36.5·1.2·10/36.5 = 12 N. Always check the units: density in g/mL, E in g/mol.

Worked examples
24.5 % H₂SO₄ (ρ = 1.2 g/mL, E = 49): C_N = 24.5·1.2·10/49 = 6 N; the molar concentration is 3 M.
A 20 % solution is 4 N with ρ = 1.25 g/mL. E = C%·10·ρ/C_N = 20·10·1.25/4 = 62.5 g/mol.
Class activity

Pair work: for one solution (for example 20 % HCl, ρ = 1.1) calculate C_M and C_N and check the relation C_N = z·C_M between them.

Practice
1
Find the normal concentration of 36.5 % HCl (ρ = 1.2 g/mL, E = 36.5).
2
A 24.5 % H₂SO₄ solution has a density of 1.2 g/mL. What is C_N in N (E = 49)?
3
A 4 N solution has a density of 1.25 g/mL and a percent concentration of 20 %. Find the equivalent mass of the solute.
4
What is the normal concentration of 2 M H₂SO₄, and why?