Acetonitrile (CH₃CN) is a polar organic solvent that dissolves a wide range of solutes, including many salts. The density of a 1.80 M LiBr solution in acetonitrile is 0.826 g/cm³. Calculate the concentration of the solution in (a) molality,

검증된 단계별 안내

Start by understanding the relationship between molarity and molality. Molarity (M) is moles of solute per liter of solution, while molality (m) is moles of solute per kilogram of solvent.

Calculate the mass of the solution using its density. Use the formula: \( \text{mass of solution} = \text{density} \times \text{volume} \). Assume 1 L of solution for simplicity, so the mass of the solution is \( 0.826 \text{ g/cm}^3 \times 1000 \text{ cm}^3 \).

Determine the moles of LiBr in the solution. Since the solution is 1.80 M, there are 1.80 moles of LiBr in 1 L of solution.

Calculate the mass of LiBr using its molar mass. The molar mass of LiBr is approximately 86.85 g/mol, so the mass of LiBr is \( 1.80 \text{ moles} \times 86.85 \text{ g/mol} \).

Find the mass of the solvent (acetonitrile) by subtracting the mass of LiBr from the total mass of the solution. Finally, calculate the molality using the formula: \( \text{molality} = \frac{\text{moles of solute}}{\text{kilograms of solvent}} \).

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Molarity

Molarity is a measure of concentration defined as the number of moles of solute per liter of solution. It is commonly used in chemistry to express the concentration of a solution. In this case, the 1.80 M LiBr solution indicates that there are 1.80 moles of lithium bromide dissolved in one liter of acetonitrile.

Molality

Molality is another measure of concentration, defined as the number of moles of solute per kilogram of solvent. Unlike molarity, which depends on the volume of the solution, molality is based on the mass of the solvent, making it useful for temperature-dependent calculations. To convert from molarity to molality, the mass of the solvent must be known.

Density

Density is defined as mass per unit volume and is a critical property in calculating concentrations. In this context, the density of the solution (0.826 g/cm³) allows for the conversion between the mass of the solution and its volume. This information is essential for determining the mass of the solvent when calculating molality from the given molarity.

Acetonitrile (CH3CN) is a polar organic solvent that dissolves a wide range of solutes, including many salts. The density of a 1.80 M LiBr solution in acetonitrile is 0.826 g/cm3. Calculate the concentration of the solution in (a) molality,