Define the strength of a solution. Write its formula.

The strength of a solution refers to the concentration of a solute within a given volume of solvent. It essentially indicates how much of a substance is dissolved in a certain amount of liquid. This concept is crucial in various fields, including chemistry, biology, and environmental science, as it helps in understanding reactions, biological processes, and pollutant levels in water, among other applications.

Understanding Solution Strength

When we talk about the strength of a solution, we often express it in terms of concentration. Concentration can be defined in several ways, but the most common methods include molarity, molality, and mass percent. Each of these measures provides insight into how much solute is present in the solution.

Molarity: A Common Measure

Molarity (M) is one of the most widely used measures of concentration. It is defined as the number of moles of solute per liter of solution. The formula for molarity is:

• Molarity (M) = moles of solute / liters of solution

For example, if you dissolve 1 mole of sodium chloride (NaCl) in enough water to make a total volume of 1 liter, the molarity of that solution would be 1 M. If you were to dissolve the same amount of NaCl in 2 liters of water, the molarity would be 0.5 M, as the solute is now spread over a larger volume.

Other Concentration Measures

While molarity is prevalent, there are other ways to express solution strength:

• Molality (m): This is defined as the number of moles of solute per kilogram of solvent. The formula is:
• Molality (m) = moles of solute / kilograms of solvent
• Mass Percent: This indicates the mass of solute as a percentage of the total mass of the solution. The formula is:
• Mass Percent = (mass of solute / mass of solution) × 100

Practical Applications

Understanding the strength of a solution is vital in many practical scenarios. For instance, in a laboratory setting, knowing the concentration of a reagent can determine how it will react with other substances. In medicine, the concentration of drugs in solutions can affect their efficacy and safety. Environmental scientists also measure the concentration of pollutants in water to assess water quality and safety.

Real-World Example

Consider a scenario where a chemist needs to prepare a saline solution for medical use. The standard saline solution is 0.9% NaCl. To prepare this, the chemist would calculate the mass of NaCl needed based on the total mass of the solution they want to create. If they aim to make 1 liter of saline solution, they would need 9 grams of NaCl, as:

• Mass Percent = (9 g / 1000 g) × 100 = 0.9%

This example illustrates how understanding the strength of a solution is essential for accurate preparation and application in real-world contexts.