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What is molarity in chemistry?
What is the formula for molarity?
What is molarity in stoichiometry?
Is molarity the same as concentration?
What are the units of molarity?
What is the molarity of a solution?
Molarity (M) is one of the most commonly used units for measuring the concentration of a solution in chemistry. It helps express how much solute (the substance being dissolved) is present in a specific volume of solvent (the substance doing the dissolving), usually water.
Jan 30, 2024 · Molarity expresses the concentration of a solution. It is defined as the number of moles of a substance or solute, dissolved per liter of solution (not per liter of solvent!). concentration = number of moles / volume
Dec 10, 2023 · The most common unit of concentration is molarity, which is also the most useful for calculations involving the stoichiometry of reactions in solution. The molarity (M) is defined as the number of moles of solute present in exactly 1 L of solution.
- Overview
- Key points
- Introduction: Mixtures and solutions
- Molar concentration
- Example 1: Calculating the molar concentration of a solute
- Example 2: Making a solution with a specific concentration
- Summary
- Try it: The stoichiometry of a precipitation reaction
Definitions of solution, solute, and solvent. How molarity is used to quantify the concentration of solute, and how to calculate molarity.
•Mixtures with uniform composition are called homogeneous mixtures or solutions.
•Mixtures with non-uniform composition are heterogeneous mixtures.
•The chemical in the mixture that is present in the largest amount is called the solvent, and the other components are called solutes.
•Molarity or molar concentration is the number of moles of solute per liter of solution, which can be calculated using the following equation:
Molarity=mol soluteL of solution
•Molar concentration can be used to convert between the mass or moles of solute and the volume of the solution.
In real life, we often encounter substances that are mixtures of different elements and compounds. One example of a mixture is the human body. Did you know that the human body is approximately 57% water by mass? We are basically an assortment of biological molecules, gases, and inorganic ions dissolved in water. I don't know about you, but I find that pretty mind-boggling!
If substances are mixed together in such a way that the composition is the same throughout the sample, they are called homogeneous mixtures. In contrast, a mixture that does not have a uniform composition throughout the sample is called heterogeneous.
[Is molar concentration the same as molality?]
The component of a solution that is present in the largest amount is known as the solvent. Any chemical species mixed in the solvent is called a solute, and solutes can be gases, liquids, or solids. For example, Earth's atmosphere is a mixture of 78% nitrogen gas, 21% oxygen gas, and 1% argon, carbon dioxide, and other gases. We can think of the atmosphere as a solution where nitrogen gas is the solvent, and the solutes are oxygen, argon and carbon dioxide.
The molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution (not per liter of solvent!):
[What is a mole?]
Molarity=mol soluteL of solution
[Why is the volume of the solution different from the volume of the solvent?]
Let's consider a solution made by dissolving 2.355g of sulfuric acid, H2SO4 , in water. The total volume of the solution is 50.0mL . What is the molar concentration of sulfuric acid, [H2SO4] ?
To find [H2SO4] we need to find out how many moles of sulfuric acid are in solution. We can convert the mass of the solute to moles using the molecular weight of sulfuric acid, 98.08gmol :
mol H2SO4=2.355g H2SO4×1mol98.08g=0.02401mol H2SO4
We can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid:
[H2SO4]=mol soluteL of solution=0.02401mol0.050L=0.48M
Concept check: What is the molar concentration of H+ ions in a 4.8M H2SO4 solution?
Sometimes we have a desired concentration and volume of solution, and we want to know how much solute we need to make the solution. In that case, we can rearrange the molarity equation to solve for the moles of solute.
mol solute=Molarity×L of solution
For example, let's say we want to make 0.250L of an aqueous solution with [NaCl]=0.800M . What mass of the solute, NaCl , would we need to make this solution?
We can use the rearranged molarity equation to calculate the moles of NaCl needed for the specified concentration and volume:
mol NaCl=[NaCl]×L of solution=0.800molL×0.250L=0.200mol NaCl
We can then use the molecular weight of sodium chloride, 58.44gmol , to convert from moles to grams of NaCl :
•Mixtures with uniform composition are called homogeneous solutions.
•Mixtures with non-uniform composition are heterogeneous mixtures.
•The chemical in the mixture that is present in the largest amount is called the solvent, and the other components are called solutes.
•Molarity or molar concentration is the number of moles of solute per liter of solution, which can be calculated using the following equation:
Molarity=mol soluteL of solution
•Molar concentration can be used to convert between the mass or moles of solute and the volume of the solution.
Molarity is a useful concept for stoichiometric calculations involving reactions in solution, such precipitation and neutralization reactions. For example, consider the precipitation reaction that occurs between Pb(NO3)2(aq) and KI(aq) . When these two solutions are combined, bright yellow PbI2(s) precipitates out of solution. The balanced equation for this reaction is:
Pb(NO3)2(aq)+2KI(aq)→PbI2(s)+2KNO3(aq)
If we have 0.1L of 0.10M Pb(NO3)2 , what volume of 0.10M KI(aq) should we add to react with all the Pb(NO3)2(aq) ?
Choose 1 answer:
Choose 1 answer:
•(Choice A)
- Calculating Molarity with Moles and Volume. Know the basic formula for calculating molarity. Molarity is equal to the number of moles of a solute divided by the volume of the solution in liters.
- Calculating Molarity with Mass and Volume. Know the basic formula for calculating molarity. Molarity expresses the relationship between the number of moles of a solute per liters of solution, or the volume of that solution.
- Calculating Molarity with Moles and Milliliters. Know the basic formula for calculating molarity. In order to find molarity, you need to calculate the number of moles of solute for a solution per liter of solution.
- Additional Practice Problem. Find the molarity of a solution made by dissolving 5.2 g of NaCl in 800 ml of water. Identify the values provided to you in the problem: mass in grams and volume in milliliters.
May 28, 2024 · As shown below, the molarity of a solution is defined as the ratio of the molar amount of solute that is present in a solution, relative to the volume of the solution, as a whole. Recall that the variable that is utilized to represent the molar quantity of a substance is "n."
Molarity is defined as the number of moles of solute per liter of solution. \[\mathrm{molarity=\dfrac{number\: of\: moles\: of\: solute}{number\: of\: liters\: of\: solution}} \label{defMolarity} \] The symbol for molarity is \(\text{M}\) or moles/liter. Chemists also use square brackets to indicate a reference to the molarity of a substance.
