Problem 9 - A Complete Resource Book in Chemistry for JEE Main

Question

The number of moles of \(\mathrm{KCl}\) in \(1000 \mathrm{~mL}\) of 3 molar solution is (a) 2 (b) 3 (c) 4 (d) 6

Step-by-Step Solution

Answer

The number of moles of KCl is 3, option (b).

Step 1: Understanding Molarity

Molarity (M) is a way to express the concentration of a solution as the number of moles of solute per liter of solution. In this problem, we have a 3 M solution, meaning there are 3 moles of KCl in every 1 liter (1000 mL) of solution.

Step 2: Identifying the Volume

The problem gives us the volume of the solution as 1000 mL. We need to convert this volume to liters to match the units used in molarity calculations. Since 1000 mL equals 1 liter, we have 1 liter of the 3 M solution.

Step 3: Calculating the Moles of KCl

Using the formula for molarity, \[ M = rac{ ext{moles of solute}}{ ext{liters of solution}} \]we substitute the known values: the molarity (3 M) and the volume in liters (1 liter). This gives us \[ 3 = rac{ ext{moles of KCl}}{1} \]Solving for moles of KCl, we obtain 3 moles of KCl.

Key Concepts

Concentration

When discussing solutions in chemistry, it's often necessary to talk about concentration. Concentration refers to the amount of a substance, known as the solute, that is dissolved in a given quantity of solvent. One common way to express concentration is in terms of molarity (M). Molarity tells us how many moles of solute are present in one liter of solution.

• This unit is denoted as mol/L or simply M.
• For example, a 3 M solution of KCl means there are 3 moles of potassium chloride dissolved in every liter of solution.

By understanding concentration, chemists can accurately describe how much of a substance is contained within a solution, which is crucial for reactions, formulations, and experiments. You'll often encounter problems where you need to calculate the concentration to proceed or verify a result.

Moles of Solute

The concept of moles of solute is a key component in understanding solutions in chemistry. The mole is a unit used to measure the amount of a substance, based on the number of atoms or molecules rather than the mass. One mole contains approximately 6.022 x 10^23 particles, which is Avogadro's number.

• When calculating the number of moles of solute, you need to know the molarity of the solution and its volume.
• In our case, with a 3 M solution of KCl in a 1-liter volume, the number of moles is straightforward: 3 moles.

Knowing moles of solute helps you understand the balancing of chemical equations and the specifics of reactions involving solutions. It's crucial for figuring out how much of a substance is needed to achieve a particular concentration or to react completely with another substance.

Solution Volume

Volume plays an integral role in understanding solutions. The solution volume is the total amount of space that a solute and solvent occupy together in a solution. In molarity calculations, volume measurements must be in liters because molarity is defined as moles per liter.

• For instance, a question might provide the volume in milliliters, requiring a conversion to liters.
• 1000 mL is equivalent to 1 liter, simplifying calculations with molarity.

Accurate volume measurement is essential for precisely determining the concentration and for ensuring that the preparation of solutions is accurate. Incorrect volume measurements can lead to errors in the concentration, which may affect experiments or industrial processes relying on precise chemical compositions.