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Introduction to Molarity
Molarity is a widely used unit of concentration in chemistry, representing the number of moles of solute present in one liter of solution. It is expressed in moles per liter (mol/L) and is often denoted by the symbol “M.”
Understanding molarity is essential for various tasks in chemistry, such as preparing solutions, performing dilutions, and carrying out chemical reactions that require specific concentrations of reactants.
Here’s a basic introduction to molarity and how to solve concentration problems:
- Molarity (M) formula:
Molarity (M) = moles of solute / liters of solution
- Preparing a solution with a specific molarity:
To prepare a solution of a specific molarity, you will need the following information:
- The desired molarity (M)
- The volume of the solution you want to prepare (V, in liters)
- The molar mass of the solute (Mm, in grams per mole)
First, calculate the moles of solute required:
moles of solute = M * V
Next, convert moles of solute to grams using the molar mass:
grams of solute = moles of solute * Mm
Now, weigh the calculated grams of solute and dissolve it in a volumetric flask. Add solvent up to the desired volume to obtain a solution with the specified molarity.
- Diluting a solution:
If you have a concentrated solution and want to dilute it to a lower molarity, you can use the dilution formula:
M1 * V1 = M2 * V2
- M1 is the initial molarity
- V1 is the initial volume
- M2 is the final molarity
- V2 is the final volume
To find the volume of the concentrated solution (V1) needed to achieve the desired molarity (M2) and final volume (V2), rearrange the formula:
V1 = (M2 * V2) / M1
Measure the calculated volume (V1) of the concentrated solution and add enough solvent to reach the final volume (V2). The resulting solution will have the desired molarity (M2).
By understanding the basic concepts of molarity and using these formulas, you can solve a variety of concentration problems in chemistry.