Mission: Mixture Mayhem — Separating Sand, Salt, and Iron Filings Using Physical Properties
Science Lab · Grade 7
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Type
science_lab
Pre Lab
Background: Have you ever wondered how scientists or engineers separate useful materials from a messy mixture? In nature and industry, mixtures of different substances must be sorted based on their **physical properties** — characteristics like magnetism, solubility, and particle size that can be observed without changing the substances chemically. A **mixture** is a combination of two or more substances that are not chemically bonded, which means they can be separated using physical means. The three substances in today's lab — sand, salt (sodium chloride), and iron filings — each have distinct physical properties that make them separable from one another.
Scientists use several **separation techniques** that exploit these differences. **Magnetism** is the ability of certain materials, like iron, to be attracted to a magnet. Because iron filings are magnetic while sand and salt are not, a magnet can pull iron filings out of the mixture without disturbing the other components. **Filtration** is a technique that separates solids from liquids by passing the mixture through a porous barrier like filter paper. Sand does not dissolve in water, so it will be caught by the filter paper while dissolved salt passes through in the liquid (called the filtrate). Finally, **evaporation** is the process by which liquid water turns into water vapor, leaving behind any dissolved solid. When salt water is gently heated on a hot plate, the water evaporates and salt crystals are left behind — a process also called **crystallization**.
In this lab, you will act as a scientist tasked with recovering as much of each pure substance as possible. The amount of a substance successfully recovered compared to how much you started with is called **recovery**, and it can be measured as a percentage using mass data. Before you begin any lab work, you will plan your investigation by proposing the order in which you will apply each separation technique and defend your reasoning to your classmates. Think carefully — does the order matter? What might happen if you tried to evaporate the water before you filtered out the sand?
Vocabulary
Term: physical properties
Definition: Characteristics of a substance that can be observed or measured without changing the substance into a different material (e.g., color, magnetism, solubility, density).
Term: magnetism
Lab Type
Post Lab
Standards
Safety Level
Teacher Notes
Estimated Time
Experiment Design
Research Question
Learning Objectives
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