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Chemists deal with amounts of molecules every day.
Our reactions are described as so many molecules of compound A reacting with so many molecules of compound B to form so many molecules of compound C. When we determine how much reagent to use, we need to know the of molecules in a given volume of the reagent. Percent solutions only tell us the of grams, not molecules. So we need another way to talk about s of molecules. Chemists primarily need the concentration of solutions to be expressed in a way that s for the of particles that react according to a particular chemical equation.
Since percentage measurements are based on either mass or volume, they are generally not useful for chemical reactions. A concentration unit based on moles is preferable. The molarity M of a solution is the of moles of solute dissolved in one liter of solution.
To calculate the molarity of a solution, you divide the moles of solute by the volume of the solution expressed in liters. Note that the volume is in liters of solution and not liters of solvent. For example a solution labeled as 1. A solution is prepared by dissolving Calculate its molarity. Step 1: List the known quantities and plan the problem. The mass of the ammonium chloride is first converted to moles. Then the molarity is calculated by dividing by liters.
Note the given volume has been converted to liters. Step 3: Think about your result. The molarity is 1.
Four ificant figures are appropriate. In a laboratory situation, a chemist must frequently prepare a given volume of solutions of a known molarity. The task is to calculate the mass of the solute that is necessary. The molarity equation can be rearranged to solve for moles, which can then be converted to grams. See sample problem A chemist needs to prepare 3. What mass of KMnO 4 does she need to make the solution? Moles of solute is calculated by multiplying molarity by liters. Then, moles is converted to grams. When g of potassium permanganate is dissolved into water to make 3.
Watch a video of molarity calculations:. Read the material and work the problems at the site below:. Search for:. Molarity Learning Objectives Define molarity.
Perform calculations involving molarity. How many molecules can be found in a reaction? Summary Calculations using the concept of molarity are described. Review What does M stand for? What does molarity tell us that percent solution information does not tell us? What do we need to know about a molecule in order to carry out molarity calculations? s and Attributions. CC d content, Shared ly.Looking for chemistry and ltr
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