Using Density and Molarity to Solve for the Percent by Mass of a Solution

Science, Math, and Chemistry
25 Sept 202010:59
EducationalLearning
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TLDRThis chemistry tutorial addresses a complex problem from an online homework assignment for Chemistry 150 students. The instructor guides students through the process of finding the percent by mass of sodium chloride in a solution with a given molarity and density. The explanation covers key concepts like solutions, solutes, molarity, and density, and demonstrates how to calculate the mass percentage of the solute. The video aims to prepare students for the upcoming week's lessons and encourages them to tackle challenging problems by integrating multiple concepts.

Takeaways
  • 📘 This session focuses on problem-solving for Chemistry 150, specifically chapter 4 from the online homework assignment.
  • 🔬 The problem is to find the percent by mass of sodium chloride in a 1.35 molarity sodium chloride solution, with the solution's density given as 1.05 grams per milliliter.
  • 📊 A solution consists of a solute (the substance being dissolved) and a solvent (the medium doing the dissolving).
  • 💧 Molarity (M) measures the concentration of a solution in moles of solute per liter of solution.
  • ⚖️ Density is the mass of a solution per unit volume, expressed as grams per milliliter.
  • 📐 To solve for the percent by mass, you need the mass of the solute and the total mass of the solution.
  • 🔄 The molarity provides moles of sodium chloride, which can be converted to grams using the molar mass (58.45 grams per mole).
  • 🧮 Assume you have one liter of solution to simplify calculations, converting the volume to mass using the given density.
  • ✖️ Calculate the mass of sodium chloride using molarity and molar mass, then determine the total mass of the solution using its volume and density.
  • 📝 The percent by mass is calculated as (mass of sodium chloride / total mass of solution) x 100, resulting in 7.52%.
Q & A

  • What is the main topic of the chemistry problem-solving session?

    -The main topic is to find the percent by mass of sodium chloride in a 1.35 molarity sodium chloride solution.

  • What is a solution in the context of chemistry?

    -A solution is a homogeneous mixture where a solute is dissolved in a solvent, typically water.

  • What are the roles of solute and solvent in a solution?

    -The solute is the substance being dissolved, and it is present in a lesser amount. The solvent is the medium that does the dissolving and is present in a larger amount.

  • What is the difference between molarity and density in measuring solution concentration?

    -Molarity is the number of moles of solute per liter of solution, while density is the mass of the solution per unit volume, typically in grams per milliliter.

  • How is molarity used as a conversion factor in this problem?

    -Molarity is used as a conversion factor to determine the amount of solute (in moles) per liter of solution, which can then be converted to grams using the molar mass of the solute.

  • What is the molar mass of sodium chloride and how is it used in the problem?

    -The molar mass of sodium chloride is 58.45 grams per mole. It is used to convert moles of sodium chloride to grams for calculating the percent by mass.

  • What does the density of 1.05 grams per milliliter signify?

    -The density of 1.05 grams per milliliter signifies that there are 1.05 grams of the solution in every milliliter of its volume.

  • How is the percent by mass of sodium chloride calculated in the solution?

    -The percent by mass is calculated by dividing the mass of sodium chloride (the solute) by the total mass of the solution (solute plus solvent) and then multiplying by 100.

  • What is the significance of the given molarity of 1.35 moles per liter in the problem?

    -The molarity of 1.35 moles per liter indicates that there are 1.35 moles of sodium chloride in every liter of the solution, which is crucial for determining the mass of the solute.

  • How does the instructor simplify the problem by assuming one liter of solution?

    -By assuming one liter of solution, the instructor can directly use the molarity and density values to calculate the mass of the solute and the solution in grams, simplifying the calculation of the percent by mass.

  • What is the final calculated percent by mass of sodium chloride in the solution?

    -The final calculated percent by mass of sodium chloride in the solution is 7.52%.

Outlines
00:00
🧪 Chemistry Problem Solving Session Introduction

This paragraph introduces a chemistry problem-solving session for Chemistry 150 students, focusing on a specific problem from an online homework assignment. The problem involves calculating the percent by mass of sodium chloride in a solution with a given molarity and density. The instructor acknowledges the complexity of the problem and its relation to upcoming lessons on solutions. The paragraph defines a solution, introduces the concepts of solute and solvent, and explains the importance of concentration in understanding solutions.

05:01
📚 Understanding Molarity and Solution Density

The second paragraph delves into the concepts of molarity and solution density. Molarity is defined as moles of solute per liter of solution, serving as a measure of solution concentration. The instructor explains how to use the given density of the solution (1.05 grams per milliliter) and the molarity of the sodium chloride solution (1.35 moles per liter) to find the mass of sodium chloride in one liter of solution. The process involves converting moles of sodium chloride to grams using the molar mass of sodium chloride (58.45 grams per mole) and then using the density to find the total mass of the solution.

10:03
🔍 Calculating Percent by Mass of Sodium Chloride

The final paragraph explains the calculation of the percent by mass of sodium chloride in the solution. The instructor demonstrates how to use the previously calculated mass of the solute (78.91 grams) and the total mass of the solution (1050 grams) to determine the percentage by mass. The calculation involves dividing the mass of the solute by the total mass of the solution and multiplying by 100 to get the percentage. The result is a 7.52% mass of sodium chloride in the solution, which is presented as a conversion factor. The paragraph concludes with encouragement for students as they tackle challenging problems in Chemistry 150.

Mindmap
Keywords
💡Percent by Mass
Percent by mass is a way to express the concentration of a solution. It is calculated as the mass of the solute divided by the total mass of the solution, multiplied by 100. In the video, the speaker explains how to find the percent by mass of sodium chloride in a solution by using the molarity and density of the solution.
💡Molarity
Molarity, denoted as M, is a measurement of the concentration of a solution expressed as the number of moles of solute per liter of solution. The video uses a 1.35 M sodium chloride solution to demonstrate how to convert between different units of concentration.
💡Density
Density is defined as the mass of a substance per unit volume, typically expressed in grams per milliliter (g/mL). In the context of the video, the density of the sodium chloride solution is used to convert between volume and mass, which is crucial for calculating the percent by mass.
💡Solution
A solution is a homogeneous mixture composed of a solute dissolved in a solvent. The video describes how sodium chloride (salt) is the solute dissolved in water (solvent) to form a saltwater solution, which is then used to discuss concentration measures.
💡Solute
A solute is the substance that is dissolved in a solvent to form a solution. In the video, sodium chloride is the solute in the saltwater solution. The speaker explains how to determine the mass of the solute when given the molarity and volume of the solution.
💡Solvent
The solvent is the substance that dissolves the solute to form a solution. In the video, water is the solvent for the sodium chloride solution. The relationship between solute and solvent is key to understanding the concept of solutions and concentration.
💡Concentration
Concentration refers to the amount of solute present in a given quantity of solvent or solution. The video discusses various ways to measure concentration, including molarity and percent by mass, and how these measurements help to understand the composition of a solution.
💡Moles
Moles are a unit of measurement for the amount of substance, used to express the number of particles (atoms, molecules, ions) present. In the video, moles of sodium chloride are calculated from molarity and then converted to grams using the molar mass for further calculations.
💡Molar Mass
Molar mass is the mass of one mole of a substance, usually expressed in grams per mole (g/mol). In the video, the molar mass of sodium chloride (58.45 g/mol) is used to convert moles of sodium chloride to grams to find the mass percent of the solution.
💡Homogeneous Mixture
A homogeneous mixture is a mixture in which the composition is uniform throughout. The video describes a saltwater solution as a homogeneous mixture where the solute (sodium chloride) is evenly distributed in the solvent (water).
Highlights

Introduction to a problem-solving session for Chemistry 150 students, focusing on a specific problem from an online homework assignment.

The problem asks for the percent by mass of sodium chloride in a 1.35 molarity solution, with a given density of 1.05 grams per mil.

Explanation of the concept of a solution, involving a solute and a solvent, with the solute being the substance dissolved.

Clarification of molarity as a measure of solution concentration, defined as moles of solute per liter of solution.

Density is described as mass over volume, with the example of 1.05 grams of solution per milliliter.

The importance of understanding different ways to measure the concentration of a solution.

The challenge of converting between density and molarity to find the percent by mass of sodium chloride.

Definition of percent by mass as the mass of the solute over the total mass of the solution (solute plus solvent).

Use of molarity to calculate the grams of sodium chloride in one liter of solution.

Conversion of moles of sodium chloride to grams using the molar mass of 58.45 grams per mole.

Calculation of the total grams of solution using the density and volume conversion from liters to milliliters.

Determination of the mass percent of sodium chloride by dividing the mass of the solute by the total mass of the solution and multiplying by 100.

Final calculation resulting in a 7.52% mass of sodium chloride in the solution.

The significance of the calculated mass percent as a conversion factor for further chemical calculations.

Emphasis on the integration of multiple concepts to solve complex chemistry problems.

Encouragement for students to understand the concepts as they progress through the course material.

Acknowledgment of the difficulty of the problem and the support provided for students to work through it.

Transcripts

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Chemistry GuideSodium ChlorideMass PercentMolarity CalculationSolution ConcentrationEducational ContentChem 150Problem SolvingChemistry HomeworkOnline Tutorial