Chemical Equilibrium and Molar Concentration

Questions and Answers

What is the molar concentration of ethanol in a solution containing 2.30g of C2H5OH in 3.50L?

0.0200 M

0.0143 M (correct)

0.0499 M

0.0020 M

Which of the following statements accurately describes analytical molarity?

It expresses the total number of moles of a solute in 1 L of the solution. (correct)

It is always equal to the equilibrium concentration of the species.

It indicates the concentration of a solute in solid form.

It can only be measured in millimoles.

What is the analytical concentration of trichloroacetic acid (HA) in the solution?

0.047 M

1.744 x 10^-3 M

0.127 M

0.174 M (correct)

In a solution with an analytical concentration of 1.0 M sulfuric acid (H2SO4), what is the equilibrium molarity of H2SO4?

0.00 M Signup and view all the answers

What is the purpose of using square brackets around a chemical formula in equilibrium molarity?

To denote the concentration of the species in a solution at equilibrium. Signup and view all the answers

What percentage of trichloroacetic acid remains undissociated in the solution?

27% Signup and view all the answers

How is the number of moles of ethanol calculated from its mass?

Mass divided by molar mass. Signup and view all the answers

How many grams of BaCl2.2H2O are needed to prepare 2.00 L of a 0.108 M solution?

52.8 g Signup and view all the answers

What is the molarity of the ionized species A- in the trichloroacetic acid solution?

0.127 M Signup and view all the answers

What best describes the term 'formal concentration' in chemistry?

It represents the analytical concentration of a solute. Signup and view all the answers

If the equilibrium concentrations of H3O+, HSO4-, and SO4-2 are 1.01 M, 0.99 M, and 0.01 M respectively, what can be inferred about H2SO4 in that solution?

H2SO4 is fully dissociated. Signup and view all the answers

If 0.0740 mol of chloride ions (Cl-) are required, how much BaCl2.2H2O must be used?

4.52 g Signup and view all the answers

Given that the molar mass of C2H5OH is 46.07 g/mol, what is the primary relevance of knowing this value in concentration calculations?

To convert between mass and moles for the solute. Signup and view all the answers

What is the equilibrium concentration of H+ ions produced from the dissociation of trichloroacetic acid?

0.127 M Signup and view all the answers

What is the total number of moles of trichloroacetic acid in a 10.0 mL solution that contains 285 mg of the acid?

0.00174 mol Signup and view all the answers

Which of the following accurately describes the preparation of a BaCl2 solution?

Dissolve solute and dilute to volume. Signup and view all the answers

Study Notes

Chemical Concentration Calculations

Molar concentration (C) is calculated as moles of solute (n) divided by volume of solution (V).
Example: For 2.30g of ethanol (C2H5OH) in 3.50L, moles calculated as:
- nC2H5OH = 2.30g / 46.07 g/mol = 0.04992 mol
- Molar concentration C = 0.04992 mol / 3.50 L = 0.0143 M

Analytical Molarity

Provides total moles of solute in 1L of solution.
Example: For a 1.0M sulfuric acid (H2SO4), dissolve 1 mol (98g) of H2SO4 in water and dilute to 1L.

Equilibrium Molarity

Indicates concentration of a particular species at equilibrium.
In a 1.0M H2SO4 solution, the equilibrium molarity of H2SO4 is 0.0M since it completely dissociates.
Corresponding equilibrium concentrations are:
- [H3O+] = 1.01 M
- [HSO4-] = 0.99 M
- [SO4²-] = 0.01 M

Distinction in Concentration Terms

Analytical concentration often referred to as formal concentration (F).
Equilibrium concentration often uses molarity (M) for species concentration.
Example: H2SO4 has a formal concentration of 1.0F and an equilibrium concentration of 0.0M.

Trichloroacetic Acid Example

Given 285 mg of trichloroacetic acid (CCl3COOH, 163.4 g/mol) in 10.0 mL:
- Moles calculated as:
  - n (HA) = 285 mg / 163.4 g/mol = 0.00174 mol
- Molar analytical concentration (CHA) = 0.00174 mol / 0.010 L = 0.174 M
73% ionization leads to:
- [HA] = 0.174 × (100 - 73)/100 = 0.047 M
- [A-] = 0.127 M
- [H+] = 0.127 M

BaCl2 Preparation Examples

To prepare 2.00L of 0.108M BaCl2 from BaCl2·2H2O (244 g/mol):
- Required moles = 2.00 L × 0.108 mol/L = 0.216 mol BaCl2·2H2O.
- Mass = 0.216 mol × 244 g/mol = 52.8 g.
- Dissolve 52.8 g in water, dilute to 2.00 L.
To prepare 500 mL of Cl⁻ solution using BaCl2·2H2O:
- Required moles of Cl⁻ = 0.0740 mol × (0.500 L × 244.3 g/mol) / (2 mol Cl⁻).
- Mass = 4.52 g BaCl2·2H2O.
- Dissolve in water and dilute to 0.500L.

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Description

Explore important concepts of chemical equilibrium, focusing on molar concentration. Learn to calculate the molar concentration of solutions using ethanol as an example. This quiz will help you understand how solute and solution volume relate in chemistry.