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Molarity, Molality, Volume & Mass Percent, Mole Fraction & Density…
Molarity, Molality, Volume & Mass Percent, Mole Fraction & Density
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A solution is a homogeneous mixture consisting of a solute dissolved into a solvent. The solute is the substance that is being dissolved, while the solvent is the dissolving medium.
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Molarity: M = mol solute / L of solvent
Molality: m = mol solute / Kg of solvent Density = Mass / Volume Density = g/ml or g/cm³
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Example: 15g of NaCl are dissolved in 225g of water. What is the mass percent of NaCl in the solution?
m% = m solute / m solution x 100%
m% = 15g of NaCl/240g x 100%
m%= 6.25% of NaCl
Example 2: 25ml of Methanol (d=0.792g/cm³) is mixed with 150ml of water (d= 1g/cm³). What is the volume % of Methanol? What is the mass % of water?
V% = V solute / V solution x 100%
V% = 25ml / 175ml x 100%
V% = 14.29 Methanol
m% = m solute / m solution x 100%
mass = Density x Volume
Mass of Methanol = 25ml x 0.792g
Mass Methnol = 19.8 g
mass of water = 150ml x 1g
mass of water = 150 g
m% = 150 g / 169.8 g x 100%
m% = 88.3% of Water
Example 3 : 2 mols of KCl is dissolved in 8 mols of water. What is the mol fraction of KCl?
Mol fraction of KCl = Number of mols of KCl / Number of Mols of KCl + Number of Mols of H2O
Mol Fraction of KCl = 2/2+8
Mol Fraction of KCl = 2/10 or 0.2
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Dilution Problems, Chemistry, Molarity & Concentration Examples, Formula & Equations
150ml of a 0.60M CaCl2 solution was mixed with 300ml of a 0.90M CaCl2 solution. What is the new consentration of the mixture?
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To decrease the concentration you need to dilute the solution like adding water or other solvent. Ex: If you have 200 ml with a molar concentration of 2M and you and 200 ml of water you will cut the concentration by 2 with the new molarity being 1M.
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Molarity: M = mol solute / L of solvent
Molality: m = mol solute / Kg of solvent Density = Mass / Volume Density = g/ml or g/cm³
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To increase the consentration you need to put more solute or decrease the solvent. Ex: If you put a open beaker in a room water will naturally evaporate and in time the volume will decrease causing the consentration to increase.
A 0.8M HCl was diluted to a final volume of 500ml.If the new consentration is 0.2M what was the original volume of the solution? How much water was added to make this happen?
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