Elements, Compounds And Mixtures
Overview
Look around any kitchen and you will find elements (the copper in wiring), compounds (the sodium chloride in your salt shaker) and mixtures (the air you breathe). Telling them apart, and separating mixtures into their components, is one of the oldest skills in chemistry.
In this lesson you will learn the definitions that distinguish elements, compounds and mixtures, explore how melting-point data reveals purity, and master five separation techniques that Edexcel tests regularly: distillation, fractional distillation, filtration, crystallisation and paper chromatography.
Objectives
- understand how to classify a substance as an element, compound or mixture
- understand that a pure substance has a fixed melting and boiling point, but that a mixture may melt or boil over a range of temperatures
- describe these experimental techniques for the separation of mixtures: - simple distillation - fractional distillation - filtration - crystallisation - paper chromatography.
- understand how a chromatogram provides information about the composition of a mixture
- understand how to use the calculation of Rf values to identify the components of a mixture
- practical: investigate paper chromatography using inks/food colourings
Mind map
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Flashcards
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Lesson Note
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Lesson Evaluation
Congratulations on completing the lesson on Elements, Compounds And Mixtures. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- Which of the following is a compound? A) Nitrogen gas (N2) B) Bronze C) Water (H2O) D) Air Answer: C
- A pure substance can be identified because it: A) Is colourless B) Has a sharp, fixed melting point C) Dissolves in water D) Cannot be filtered Answer: B
- Which separation technique would you use to obtain pure water from salt water? A) Filtration B) Crystallisation C) Simple distillation D) Paper chromatography Answer: C
- In paper chromatography, what is the mobile phase? A) The pencil line B) The paper C) The solvent D) The spots Answer: C
- An Rf value of 0.75 means the substance has travelled: A) 75% of the distance to the solvent front B) 75% of the total paper length C) 25% of the distance to the solvent front D) Three quarters of the way to the top of the paper Answer: A
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