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Calculate the molarity (molar concentration) of a solution by entering the amount of solute and the volume of solution.
Calculate the molality of a solution by entering the amount of solute and the mass of solvent.
Convert between mass and moles for a selected compound.
Calculate the concentration of a solution after dilution using the equation c₁v₁ = c₂v₂.
Calculate the volume of titrant needed to reach the equivalence point.
Molarity (M) is the moles of solute per liter of solution. It is one of the most common ways to express concentration in laboratory settings.
Formula: M = moles of solute / volume of solution in liters
Units: mol/L or M
Applications: Laboratory preparations, titrations, reaction stoichiometry
Example: A 0.5 M HCl solution contains 0.5 moles of HCl per liter of solution
Limitation: Molarity changes with temperature as the volume of a solution expands or contracts with temperature changes
Molality (m) is the moles of solute per kilogram of solvent. This concentration unit is particularly useful for calculations involving colligative properties.
Formula: m = moles of solute / mass of solvent in kilograms
Units: mol/kg
Applications: Freezing point depression, boiling point elevation, vapor pressure studies
Example: A 1 m NaCl solution contains 1 mole of NaCl dissolved in 1 kilogram of water
Advantage: Unlike molarity, molality doesn't change with temperature because it depends on mass, not volume
The relationship between mass and moles is fundamental to chemistry calculations and is given by the molar mass of the substance.
Mass to Moles: Moles = Mass (g) / Molar Mass (g/mol)
Moles to Mass: Mass (g) = Moles × Molar Mass (g/mol)
Molar Mass: The mass of one mole of a substance, numerically equal to its molecular or formula weight in g/mol
Example: The molar mass of H₂O is 18.02 g/mol, so 36.04 g of water contains 2 moles
Note: Moles provide a way to count atoms and molecules on a macroscopic scale
When diluting a solution, the amount of solute remains constant while the volume increases, resulting in a decrease in concentration.
Formula: c₁v₁ = c₂v₂
Where c₁ and v₁ are the initial concentration and volume, and c₂ and v₂ are the final concentration and volume.
Applications: Preparing solutions of lower concentration from stock solutions, standardizing titrants
Example: Diluting 10 mL of 5 M HCl to 100 mL will result in a 0.5 M HCl solution
Note: This equation assumes that the solute amount remains constant during dilution
Titration is a technique to determine the concentration of a solution by reacting it with a standard solution of known concentration.
Key Components:
Equivalence Point: The point at which the moles of titrant have exactly reacted with the moles of analyte, according to their stoichiometric ratio.
Formula: moles analyte × equivalents = moles titrant × equivalents
Example: For a strong acid-strong base titration, 1 mole of H⁺ reacts with 1 mole of OH⁻
Applications: Acid-base determinations, redox reactions, complexometric analyses, precipitation reactions
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Solution concentration is a fundamental concept in chemistry that describes the amount of a solute dissolved in a specific amount of solvent or solution. Different concentration units serve different purposes in chemical calculations, with molarity and molality being among the most commonly used measures.
Molarity (symbol: M) measures the number of moles of solute per liter of solution, making it useful for laboratory work where volumes are easily measured. However, molarity changes with temperature as the volume of the solution expands or contracts. In contrast, molality (symbol: m) measures moles of solute per kilogram of solvent, providing a temperature-independent concentration measure that's particularly valuable in thermodynamic calculations.
Understanding how to convert between concentration units, calculate solution dilutions, and perform titration calculations is essential for many chemical processes. These calculations help chemists prepare solutions of specific strengths, analyze unknown samples, and predict chemical reactions in various fields including pharmaceutical development, environmental monitoring, and industrial manufacturing.