If you're seeing this message, it means we're having trouble loading external resources on our website. Show If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked. Molarity is a unit of concentration, measuring the number of moles of a solute per liter of solution. The strategy for solving molarity problems is fairly simple. This outlines a straightforward method to calculate the molarity of a solution. The key to calculating molarity is to remember the units of molarity (M): moles per liter. Find the molarity by calculating the number of moles of the solute dissolved in liters of a solution. Sample Molarity Calculation
This example has neither the moles nor liters needed to find molarity, so you must find the number of moles of the solute first. To convert grams to moles, the molar mass of the solute is needed, which can be found on certain periodic tables.
Use this number to convert grams to moles.
Now the liters of solution is needed. Keep in mind, this is the total volume of the solution, not the volume of solvent used to dissolve the solute. This example is prepared with "enough water" to make 750 mL of solution. Convert 750 mL to liters.
This is enough to calculate the molarity.
The molarity of this solution is 0.20 M (moles per liter). Quick Review of Calculating MolarityTo calculate molarity:
Make certain to use the correct number of significant figures when reporting your answer. One easy way to track the number of significant digits is to write all your numbers in scientific notation. Cite this Article Format mla apa chicagoYour Citation Helmenstine, Todd. "How to Calculate Molarity of a Solution." ThoughtCo. https://www.thoughtco.com/calculatemolarityofasolution606823 (accessed December 27, 2022). Molarity is the number of moles of a substance in one litre of solution. The official symbol for molarity is “c” (concentration), but many people use the old symbol “M”. #M = n/V#, where#n#is the number of moles and#V#is the volume in litres. We can rearrange this equation to get the number of moles: #n = M × V# Example Solution: #n = 0.300 color(red)(cancel(color(black)("L soln"))) × "0.400 mol NaCl"/(1 color(red)(cancel(color(black)("L soln")))) = "0.120 mol NaCl"# Molarity is used to measure the concentration of a solution. It is used to calculate the volume of solvent or the amount of solute. Molarity is the concentration of a solution or substance in solution, measured as the number of moles of solute per liter of solution. It is denoted by the upper case letter “M.” The smallest particle of matter which can take part in a chemical reaction is called the atom. Molecule is formed by two or more atoms tightly bound together. Mole is a fundamental SI unit. It is used to measure the amount of substance. A mole of any substance (atom, molecule, etc.) is 6.022 × 1023 molecules. Molecular mass is defined as the sum of atomic masses of all atoms in a molecule of a substance. It is expressed in the atomic mass unit (u). For example, 2H+ + O2 ⇢ H2O = 1×2 +16 = 18u Dilution is the process by which a solution is made by the addition of more solvent to make it less concentrated. The concentration of a solution is the amount of solute in a solution. There is a difference between molarity and molar mass, molarity is the number of moles of solute per liter of solution, whereas molar mass is the number of grams per mole of some substance. Calculating MolarityMolarity is defined as the number of moles of solute that is dissolved in one liter of solution. It is also known as molar concentration and is denoted by the letter “M.” Molarity Formula
To calculate the molarity of a solution by using the above formula,
Sample ProblemsProblem 1: What is the molarity of a solution by dissolving 42.5g of H2SO4 in 1 liter of the solution? Solution:
Problem 2: If seawater contains 40g of sodium chloride per 500ml, then what is the molarity of a solution? Solution:
Problem 3: How many moles of Na2CO3 are present in 15L of a 2M solution? Solution:
Problem 4: In a 20.0ml HCL of 2.0 M solution, how many moles are present? Solution:
Problem 5: How many grams of H2SO4 in weight are required to make 950ml of 0.500 M solution? Solution:
Problem 6: How many grams of Ca(OH)2 are needed to make 250 ml of 0.350M solution? Solution:
Problem 7: What is the total volume in ml of 10.0M HCl is needed to contain 5.00 moles of HCl solution? Solution:
Problem 8: What is the molarity of 25g of NaCl solution, which is dissolved in water to produce 2L of the solution? How do you calculate liters in molarity?The most common way to express solution concentration is molarity (M), which is defined as the amount of solute in moles divided by the volume of solution in liters: M = moles of solute/liters of solution.
How do you turn moles into liters?To convert between moles and liters you need to remember that one mole of a gas occupies 22.4 liters. When going from moles to liters you multiply by 22.4.
