Mixtures & Filtration

Overview

This 60-minute lesson provides 9th grade students an immersive, hands-on experience in separating mixtures through a simulated "rock salt" lab involving NaCl and rock samples. Aligned with the Next Generation Science Standards (NGSS), students will develop a deep understanding of mixtures, physical properties, and separation techniques, including filtration and evaporation. They will practice scientific inquiry, data collection, and analysis while engaging collaboratively.

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Learning Objectives

By the end of this lesson, students will:

• HS-PS1-3: Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.
• HS-PS1-2: Construct and revise an explanation based on evidence about the separation of mixtures using physical methods.
• Understand and explain dissolution, filtration, evaporation, and physical separation techniques.
• Measure and calculate mass changes before and after separation to quantify mixture components.
• Develop and refine collaboration and communication skills through lab teamwork and discussions.

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Standards Alignment

NGSS Standard	Practice/Disciplinary Core Idea/Crosscutting Concept
HS-PS1-3	Planning and Carrying out Investigations / Structure and Properties of Matter
HS-PS1-2	Constructing Explanations and Designing Solutions / Chemical Reactions
Science & Engineering Practice: Planning and Carrying Out Investigations
Crosscutting Concept: Structure and Function

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Materials Needed (per group of 3 students)

• "Rock salt" mixture: table salt (NaCl) + small clean rock chips or gravel
• Beakers or clear plastic cups
• Filter paper or coffee filters
• Funnels
• Stirring rods or spoons
• Evaporation dishes or shallow trays
• Digital scales (precision ±0.01 g)
• Hot plates (teacher operated) or heating lamps for evaporation
• Safety goggles and gloves
• Lab notebooks
• Whiteboard and markers

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Lesson Activities

1. Introduction & Review (10 minutes)

• Engage: Begin with a brief review question: How can we separate mixtures? Discuss common physical methods (filtration, evaporation, decanting).
• Brief video demo (2-3 mins) by teacher or animation on rock salt separation emphasizing key physical changes (dissolution, filtration, evaporation).
• Link to previous lesson content: Review what mixtures and solutions are and recap solubility of NaCl in water.
• Set objectives: Share today’s goal to recreate the rock salt lab safely and measure the components through separation.

2. Lab Simulation Setup & Procedure (30 minutes)

• Group formation: Arrange students in groups of 3, assign roles: measurer, recorder, filter operator.
• Procedure outline (teacher models briefly):
  1. Weigh the initial "rock salt" mixture and record mass.
  2. Add a measured amount of water to dissolve salt while stirring carefully.
  3. Filter out the undissolved rocks using filter paper and funnels. Collect the filtrate in a clean beaker.
  4. Weigh the rocks on filter paper post-filtration; record mass.
  5. Evaporate water from filtrate (teacher-monitored hot plate or lamp).
  6. Weigh the recovered salt residue after drying; record mass.
• Safety reminder: Emphasize goggles, no ingestion, and proper handling of materials and heat.
• Teacher circulates: Provide guidance, enforce safety, ask probing questions on observations and mass conservation.

3. Data Analysis & Reflection (10 minutes)

• Have groups calculate:
  • Mass of original mixture
  • Mass of rocks obtained after filtration
  • Mass of salt recovered after evaporation
  • Percent composition of each component in the original mixture
• Facilitate guided discussion:
  • Why does the mass of salt recovered sometimes differ from original expectation?
  • How does this relate to purity and possible experimental errors?
  • How could the method be improved?
• Record key points from student insights on the whiteboard.

4. Wrap-Up & Formative Assessment (10 minutes)

• Quick write: Students individually write a paragraph answering:
  • How do physical properties allow us to separate mixtures?
  • What evidence supports that filtration and evaporation effectively separate NaCl from rocks?
• Exit ticket: Each student submits a 3-sentence summary of today’s experiment and one question they still have.
• Collect and review to inform next lesson’s content.

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Differentiation & Extensions

• For advanced students: Challenge to research and explain ionic bonding related to NaCl dissolution.
• For students needing support: Provide step-by-step printed lab procedure with visuals.
• Use manipulatives or virtual lab simulations if physical materials unavailable.

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Teacher Notes

• Prepare all materials in advance.
• Ensure only safe, non-toxic rocks or gravel are used.
• Pre-weigh mixtures for uniformity if possible.
• Manage time tightly during evaporation phase; teacher may expedite drying with warm lamp.

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By the end of this lesson, students will have a practical and conceptual grasp of mixture separation via physical methods, as specified in NGSS, bridging classroom learning with authentic scientific inquiry. This "lab review" actively engages communication, collaboration, and critical thinking skills necessary for scientific literacy.