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Understanding Percent Concentration in Solutions

In this lesson, we explore how to express the concentration of a solution using percent concentration. Students will learn to differentiate between homogeneous and heterogeneous mixtures, identify solutes and solvents, and calculate percent concentration based on grams of solute and solution mass. The curriculum includes guided examples, homework review, and practical problems involving common substances like saltwater and glucose solutions. By the end of the session, students will confidently understand and apply the concept of percent concentration in various contexts.

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Understanding Percent Concentration in Solutions

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  1. Solutions Day 2 Chemistry Ms. Boon 11.28.12

  2. Objective Catalyst • I can express the concentration of a solution by percent concentration. Agenda • Catalyst • Homework review • Percent concentration • Exit slip HW: Read pp. 460-464, 468-470 Problems pp. 488 #4, 16, 21, 25 • Identify the following substances as homogeneous mixtures or heterogeneous mixtures: • Milk • Gasoline • Muddy water • Steel • Coffee • Ink • Crude oil • Bronze • Brass • seawater

  3. Homework Review: pp. 459 The solvent is the substance in excess. There is more of it. The solute is the substance dissolved in the solvent. (a) solvent: water; solute: carbon dioxide (b) solvent: water; solute: apple extract (c) solvent: water; solute: coffee filtrate (d) solvent: water; solute: salt No. A solution is any homogeneous mixture and can be gas & gas or solid & solid. (example: air or brass) 12. Water is evaporating, leaving behind the solute which is salt.

  4. Solutions Mini-Review • A solution is a homogeneous mixture. • In a solution, the solute is distributed evenly throughout the solvent.

  5. Solutions Mini-Review • Therefore, any part of a solution has the same ratio of solute to solvent as any other part of the solution. • This ratio (or comparison) of solute to solvent is called concentration.

  6. Percent Concentration • One way to express concentration is by using a percentage. • Percentage concentration is the number of grams of solute per 100 grams of solution. • % concentration = g solute___ x 100% • g solution Example: Roundup weed killer is a solution containing 18% chemical pesticide. There are 18 g pesticide for every 100 g solution.

  7. Finding the Percent Concentration % concentration = g solute___ x 100% g solution The denominator is the mass of solution. Add: g solute + g solvent Example 1: What is the percentage by mass of a solution made by dissolving 0.5 g of glucose in 9.5 g of water?

  8. Finding the Percent Concentration % concentration = g solute___ x 100% g solution The denominator is the mass of solution. Add: g solute + g solvent Example 2: What is the percentage by mass of a solution containing 12.70 g of water and 0.49 g of potassium sulfate (K2SO4)?

  9. Finding the Percent Concentration % concentration = g solute___ x 100% g solution The denominator is the mass of solution. Add: g solute + g solvent The units must be grams. If given moles, multiply by the molar mass. Example 3: What is the percentage by mass of a salt water solution made by dissolving 0.5 molNaCl in 500 g water?

  10. Finding the Percent Concentration % concentration = g solute___ x 100% g solution The denominator is the mass of solution. Add: g solute + g solvent If given the %, work backwards to find the unknown mass. Example 4: A student wants to make a 5.0% solution of rubidium chloride and water with 10.0 g rubidium chloride. How much water is needed?

  11. Exit Slip Show all your work and label your answer with the correct units. A chemist dissolves 20 g silver nitrate in 180 g water. What is the percent concentration? A glass of koolaid contains 4.0 g sucrose and 96 g water. What is the percent concentration? A fish tank contains 4 molNaCl (salt) and 1000 g water. What is the percent concentration?

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