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Questions and Answers
What is the formula to find the moles of a substance?
What is the formula to find the moles of a substance?
When preparing a solution from a solid solute, what is the first step?
When preparing a solution from a solid solute, what is the first step?
What is the purpose of filling the flask about half full with water when preparing a solution from a solid solute?
What is the purpose of filling the flask about half full with water when preparing a solution from a solid solute?
How many grams of solid NaCl are required to make 250 mL of a 0.10 M NaCl solution?
How many grams of solid NaCl are required to make 250 mL of a 0.10 M NaCl solution?
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What is the molar mass of glucose (C₆H₁₂O₆)?
What is the molar mass of glucose (C₆H₁₂O₆)?
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How many grams of glucose are required to prepare 500 mL of a 0.04 M glucose solution?
How many grams of glucose are required to prepare 500 mL of a 0.04 M glucose solution?
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What is the purpose of inverting the flask after filling it to the mark with water?
What is the purpose of inverting the flask after filling it to the mark with water?
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Study Notes
Molarity
- Molarity is the measure of the number of moles of a substance in a solution
- The formula to find the moles of a substance is: n = m/MW (where n is the number of moles, m is the mass of the substance, and MW is the molar mass)
Preparing Solutions
- Solutions can be prepared by: • Using a solid solute • Diluting a concentrated solution
- To prepare a solution from a solid solute, the molarity equation is used to determine the mass of the solute required
- Steps involved in preparing a solution from a solid solute: • Calculate the amount of solid required • Mass out the solid • Place the solid in an appropriate volumetric flask • Fill the flask about half full with water and mix • Fill to the mark with water and invert to mix
Example Problems
Preparing a Solution from Solid Solute
- To prepare 250 mL of a 0.10 M NaCl solution: • Calculate the number of moles of NaCl required: n = 0.10 M x 0.25 L = 0.025 moles • Calculate the mass of NaCl required: m = 0.025 moles x 58.44 g/mol = 1.46 g • Steps to prepare the solution: mass out 1.46 g of NaCl, place in a volumetric flask, fill half full with water and mix, fill to the mark with water and invert to mix
Preparing a Solution from Solid Solute
- To prepare 500 mL of a 0.04 M glucose solution: • Calculate the number of moles of glucose required: n = 0.04 M x 0.5 L = 0.02 moles • Calculate the molar mass of glucose: C₆H₁₂O₆ = 6(12) + 12(1) + 6(16) = 180 g/mol • Calculate the mass of glucose required: m = 0.02 moles x 180 g/mol = 3.6 g • Steps to prepare the solution: mass out 3.6 g of glucose, place in a volumetric flask, fill half full with water and mix, fill to the mark with water and invert to mix
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