Overview:

This document provides a briefing on the main themes and important ideas presented in the "Separation Techniques Lower Secondary Science" resource from Open Educational Resources / Open Source Physics @ Singapore. This resource is designed for Secondary One or Secondary Two Express and Normal Academic students taking Lower Secondary Science. It introduces the necessity of separating mixtures and explains various common separation techniques, emphasizing the underlying physical properties that enable these separations. The resource utilizes short videos and includes questions to check student understanding.

Main Themes and Important Ideas:

1. The Need for Separation of Mixtures:

• Many substances in our daily lives are mixtures containing useful constituents.
• Separation is crucial to obtain these constituents in a usable form.
• Crude oil is given as a prime example where separation into different constituents is necessary for efficient use.
• The resource highlights that often, achieving complete separation requires using more than one technique in sequence.
• It prompts students to consider not just whether to separate but also why, how, and what is being separated.
• Quote: "Many substances that we see around us are mixtures. These mixtures contain constituents that are useful to us in our daily lives. For example, crude oil must be separated into its different constituents before each constituent can be used efficiently."

1. The Role of Physical Properties in Separation:

• Successful separation relies on understanding and exploiting the differences in physical properties of the constituents within a mixture.
• The resource emphasizes that these differences are key to selecting the most appropriate separation technique.
• Quote: "In order to carry out the separation of these mixtures successfully, we will need to appreciate how the differences in physical properties of the constituents will enable us to separate them successfully."

1. Common Separation Techniques Explained:

• The resource details several common separation techniques relevant to Lower Secondary Science, using short videos as a primary mode of explanation. These techniques include:
• Magnetic Attraction: Used to separate magnetic materials (like iron) from non-magnetic materials. It's crucial to note that not all metals are magnetic (e.g., gold).
• Quote: "For magnetic separation, it is vital to highlight to students that this method is not used to separate metals from non-metals as some metals, like gold , are not attracted to magnets. Hence, this method is commonly used to separate some metals (that are magnetic) from non-metals (that are all non-magnetic) in the context of LSS."
• Paper Chromatography: Effective for separating small amounts of soluble substances based on their different solubilities in a chosen solvent. Selecting the appropriate solvent (not always water) is essential and often requires solubility tests.
• Quote: "For paper chromatography, it should be highlighted to the students that this method will only work if the constituents are soluble in the solvent provided. Hence, solubility tests are often conducted to select an appropriate solvent before chromatography can be carried out. It will be good to remind students that there are solvents other than water even though water is the more common solvent at LSS."
• Filtration: Used to separate an insoluble solid from a liquid. The resource suggests supplementing filtration with decanting (carefully pouring off the liquid) to speed up the process, but only if the solid residue does not float. It also emphasizes the importance of not discarding the filtrate if it contains a dissolved substance of interest.
• Quote: "For filtration, it can be supplemented with decanting (pouring away the top layer of liquid) first to remove part of the liquid so as to speed up the process of filtration. However, it is advisable that decanting should be done only if the residue does not float on the surface of the liquid."
• Evaporation and Distillation:Evaporation: Used to obtain a dissolved solid from a solid-liquid mixture by heating the liquid to dryness. This requires the solid to be thermally stable (high melting point in LSS context) to withstand the heating. The resource prompts students to consider why this wouldn't work for sugar in water (sugar can decompose upon strong heating).
• Quote: "For heating to dryness, the solid should be thermally stable to withstand the strong heating towards the end of the process. In the context of LSS, the term 'high melting point' is used instead of 'high thermal decomposition temperature' to facilitate understanding at LSS level."
• Distillation: Used to obtain a pure liquid from a dissolved solid-liquid or liquid-liquid mixture by exploiting significant differences in boiling points. The liquid with the lower boiling point evaporates, then condenses to form the pure liquid. Fractional distillation for more complex liquid mixtures is mentioned as a topic for higher levels.
• Quote: "For simple distillation, the key idea is that the two constituents in the mixture to be separated should have significantly different boiling points in order for this method to be successful."

1. Assessment of Understanding:

• The resource includes multiple-choice and fill-in-the-blanks questions to check students' comprehension of the concepts.
• These questions focus on identifying appropriate separation techniques for given mixtures and understanding the principles behind each technique (e.g., solubility in chromatography, boiling point differences in distillation).
• Examples of questions and correct/incorrect feedback are provided within the excerpt.

1. Emphasis on Practical Application:

• The description mentions the use of videos to explain each technique, suggesting a visual and potentially real-world context for learning.
• The examples used (e.g., separating green beans from salt solution, obtaining salt from salt water) are relatable to everyday experiences.

Key Takeaways:

• Separation techniques are essential for obtaining useful substances from mixtures found in our surroundings.
• The choice of separation technique depends on the different physical properties of the components in the mixture.
• Common separation techniques for Lower Secondary Science include magnetic attraction, paper chromatography, filtration (often with decanting), evaporation, and distillation.
• Understanding the principles behind each technique (e.g., solubility, magnetic properties, boiling points) is crucial for effective separation.
• Often, a combination of separation techniques is required to isolate all the desired constituents from a complex mixture.

This resource provides a foundational understanding of separation techniques suitable for lower secondary science students, utilizing a multimedia approach and incorporating assessment to reinforce learning..

Separation Techniques: A Study Guide

Introduction

This study guide is designed to help you review your understanding of common separation techniques in science. It covers the necessity of separating mixtures and explores various methods based on the physical properties of substances.

Key Concepts

• Mixture: A substance comprising two or more components not chemically bonded.
• Constituents: The individual substances that make up a mixture.
• Physical Properties: Characteristics of a substance that can be observed or measured without changing its chemical composition (e.g., solubility, boiling point, melting point, magnetic properties).
• Soluble: Capable of being dissolved in a solvent.
• Insoluble: Incapable of being dissolved in a solvent.
• Solvent: A substance that dissolves a solute, resulting in a solution.
• Solution: A homogeneous mixture where one or more substances (solutes) are dissolved in another substance (solvent).
• Residue: The solid material remaining after filtration or evaporation.
• Filtrate: The liquid that passes through the filter during filtration.
• Distillate: The condensed liquid collected during distillation.
• Chromatography Paper: A special paper used in paper chromatography to separate substances based on their different solubilities.

Common Separation Techniques

• Magnetic Separation: Used to separate magnetic materials (like iron) from non-magnetic materials. This method relies on the physical property of magnetism.
• Paper Chromatography: Used to separate small amounts of soluble substances from a mixture based on their different solubilities in a given solvent. The more soluble a substance, the further it travels along the chromatography paper.
• Filtration: Used to separate an insoluble solid from a liquid. The mixture is passed through a filter paper, which traps the solid residue while allowing the liquid (filtrate) to pass through. Decanting can sometimes be used as a preliminary step to remove some liquid before filtration.
• Evaporation: Used to obtain a dissolved solid from a solution by heating the liquid solvent until it evaporates, leaving the solid behind. This method is effective when the solid has a much higher melting point than the boiling point of the liquid.
• Distillation: Used to separate a pure liquid from a solution (solid-liquid mixture) or a mixture of liquids with significantly different boiling points. The liquid with the lower boiling point evaporates, is then cooled and condensed back into a liquid (distillate).
• Heating to Dryness: Similar to evaporation, this technique involves heating a solution until all the liquid evaporates, leaving behind a solid residue. It is applicable when the solid is thermally stable at the heating temperatures.

Why Separate Mixtures?

• To obtain useful constituents from raw materials (e.g., separating crude oil into gasoline, kerosene, etc.).
• To purify substances.
• To analyze the components of a mixture.

Important Considerations

• Most mixtures require more than one separation technique to isolate all their constituents effectively.
• The choice of separation technique depends on the differences in the physical properties of the substances in the mixture.
• Understanding the solubility of substances is crucial for techniques like paper chromatography and filtration (when used with a solvent).
• The boiling points of liquids are the key factor in distillation.
• The thermal stability (or high melting point as referred to in the source for LSS) of a solid is important for heating to dryness.

Quiz

Answer the following questions in 2-3 sentences each.

1. Why is it often necessary to separate mixtures in our daily lives? Provide an example from the text.
2. Explain the principle behind magnetic separation. What limitation of this technique is highlighted in the source?
3. Describe how paper chromatography works to separate substances in a mixture. What property of the constituents is key to this method?
4. Explain the process of filtration. Under what circumstance might decanting be a useful preliminary step?
5. What is the main principle behind separation by evaporation? Why is it important for the solid to have a relatively high melting point?
6. Describe the process of distillation. What physical property must be significantly different for the components of a liquid mixture to be separated effectively by simple distillation?
7. According to the text, what knowledge is crucial for successfully separating mixtures?
8. Explain why dissolving in water followed by filtration would not be a suitable method to separate a mixture of sugar and salt.
9. What are the two main processes involved in the separation technique of distillation?
10. In the context of Lower Secondary Science (LSS), what term is used instead of "high thermal decomposition temperature" when discussing heating to dryness, and why?

Answer Key

1. It is often necessary to separate mixtures to obtain useful constituents. For example, crude oil must be separated into different constituents before each can be used efficiently in various applications.
2. Magnetic separation works by using a magnet to attract and separate magnetic materials from non-magnetic materials. A key limitation is that not all metals are magnetic (e.g., gold), so this method cannot separate all metals from non-metals.
3. Paper chromatography separates substances based on their different solubilities in a solvent as they travel across chromatography paper. Substances that are more soluble in the solvent will travel further up the paper than those that are less soluble.
4. Filtration is a separation technique used to separate an insoluble solid from a liquid by passing the mixture through a filter. Decanting can be used as a preliminary step to pour away some of the liquid, speeding up the filtration process, provided the residue does not float.
5. Evaporation works by heating a solution to vaporize the liquid solvent, leaving behind the dissolved solid. It is important for the solid to have a relatively high melting point so that it does not melt or decompose during the heating process.
6. Distillation is a process involving boiling a liquid mixture and then condensing the vapor to obtain a purified liquid. For simple distillation to be effective in separating a liquid-liquid mixture, the constituents must have significantly different boiling points.
7. Successful separation of mixtures is dependent on a clear understanding of the physical properties of the constituents within each mixture. These differences in physical properties guide the selection of the most appropriate separation technique.
8. Dissolving a mixture of sugar and salt in water would create a solution where both substances are dissolved. Subsequent filtration would not be able to separate the dissolved sugar from the dissolved salt because both have become part of the liquid phase.
9. The two main processes involved in distillation are boiling (or evaporation) of the liquid with the lower boiling point and the subsequent condensation of that vapor to obtain the purified liquid.
10. In the context of LSS, the term "high melting point" is used instead of "high thermal decomposition temperature" to facilitate understanding at the lower secondary level when discussing the suitability of heating to dryness for certain solids like salt.

Essay Format Questions

1. Discuss the importance of understanding the physical properties of the constituents when choosing a separation technique for a given mixture. Provide specific examples of how different physical properties are utilized in at least three different separation techniques discussed in the text.
2. Many real-world mixtures require a sequence of separation techniques to isolate their individual components. Describe a hypothetical mixture containing at least three different types of constituents (e.g., a magnetic solid, a soluble solid, and a liquid) and outline a logical sequence of separation techniques that could be used to separate them. Explain the principle behind each chosen technique in the sequence.
3. Compare and contrast the separation techniques of evaporation and distillation. In what types of mixtures is each technique most suitable, and what are the key differences in the substances that can be recovered by each method?
4. Critically evaluate the limitations and applications of paper chromatography and magnetic separation. Discuss the types of mixtures for which each technique is effective and identify situations where they would not be suitable.
5. The text emphasizes that multiple separation techniques are often needed to fully separate a complex mixture. Explain why this is the case, using examples from the common separation techniques discussed. Consider the challenges posed by mixtures with components having similar physical properties.

Glossary of Key Terms

• Constituents: The individual substances or components that make up a mixture.
• Decanting: A process of pouring a liquid from a container while leaving any solid sediment or another immiscible liquid behind.
• Distillation: A separation technique that involves boiling a liquid and then condensing the vapor to separate it from dissolved solids or other liquids with different boiling points.
• Filtrate: The liquid that has passed through a filter.
• Filtration: A separation technique used to separate insoluble solids from liquids by passing the mixture through a porous material that retains the solid particles.
• Heating to Dryness: A separation technique where a solution is heated until the liquid evaporates completely, leaving behind the dissolved solid.
• Insoluble: Incapable of being dissolved in a particular solvent.
• Magnetic Separation: A technique used to separate magnetic materials from non-magnetic materials using a magnet.
• Mixture: A substance made up of two or more components that are not chemically bonded.
• Paper Chromatography: A separation technique used to separate dissolved substances based on their different rates of travel across a sheet of filter paper due to differences in solubility in a solvent.
• Physical Properties: Characteristics of a substance that can be observed or measured without changing its chemical composition, such as boiling point, melting point, solubility, and magnetism.
• Residue: The solid material that remains on the filter paper after filtration or in the container after evaporation.
• Soluble: Capable of being dissolved in a particular solvent.
• Solute: A substance that is dissolved in a solvent to form a solution.
• Solution: A homogeneous mixture in which one or more solutes are dissolved in a solvent.
• Solvent: A substance that dissolves a solute to form a solution.
• Thermally Stable: Able to withstand high temperatures without decomposing.

 

poly course https://www.rp.edu.sg/SAS/full-time-diplomas/Details/diploma-in-materials-science Diploma in Materials Science (R17)

 

Paper chromatography

This separation technique is used to separate small amounts of substances from mixtures, based on the different solubilities of the substances in a particular solvent.

Let's watch the following video to help us understand this technique better.

poly course https://www.rp.edu.sg/schools-courses/courses/full-time-diplomas/full-time-courses/modules/index/A364  A364 Analytical Instrumentation

Filtration

Filtration is a separation technique used to separate a solid substance from the liquid in an insoluble solid-liquid mixture.

In the following video, we will examine how filtration can be used in our daily lives.

Evaporation and Distillation

Evaporation is a separation technique used to obtain a dissolved solid substance in a solid-liquid mixture. The melting point of the solid in the mixture must be relatively higher than the boiling point of the liquid in the mixture in order for this technique to be used successfully. Usually, the mixture will be heated to dryness to evaporate the liquid completely in order to leave the solid behind.

Distillation is a separation technique used to obtain a pure liquid from a dissolved solid-liquid or liquid-liquid mixture. The basis of this technique is centred on the significantly different boiling points of the substances present in the mixture. The liquid constituent with the lower boiling point will evaporate to form a gaseous substance. This gaseous substance will eventually be condensed to obtain the pure substance in the liquid form.

Let's watch the following video to understand more about the use of these two techniques in our daily lives.

 

https://www.polytechnic.edu.sg/introduction/available-courses

Applied Chemistry , Biomedical Science , Chemical & Biomolecular Engineering , Chemical & Pharmaceutical Technology, Chemical Engineering, Environmental & Water Technology, Environmental Science, Food Science & Nutrition, Food, Nutrition & Culinary Science, Materials Science

Q1. MCQ Evaporation is a separation technique that can be used to obtain __________ solids from a solution. 

soluble

That is right! This separation technique allows us to obtain the dissolved solids from a solution by removing the solvent.

insoluble

This is incorrect. Since the insoluble solids are in a different state from the liquid solvent, a more suitable and convenient separation technique is by the use of filtration.

Q2. MCQ In which of the following cases can filtration be used to separate a mixture of two solid substances with the help of a solvent?

Both substances are soluble in the same solvent.

Good try but this is incorrect. If both substances are soluble in the same solvent, a solution containing both substances is formed. Filtration cannot separate one substance from the other.

Both are insoluble in the same solvent.

Good try but this is incorrect. If both substances are insoluble in the solvent, filtration will only separate the solvent from the mixture and not one solid substance from the other.

One is soluble while the other is insoluble in the same solvent.

Well done! When only one of the two substances in a mixture is soluble in the solvent, it dissolves and leaves the other insoluble substance behind. This insoluble substance can then be filtered off.

Q3. MRQ Which of the following mixtures cannot be separated by performing the following separation techniques in sequence: dissolving in water followed by filtration? (You may choose more than one answer.)

Iron filings and sulfur powder

Well done! Both iron filings and sulfur powder are insoluble in water and hence cannot be separated with this proposed sequence as filtration will not be able to separate these two substances from each other.

Sand and salt.

That is incorrect. The proposed sequence is workable. Salt is soluble in water but sand is not. The salt dissolves in water and the sand can then be filtered off.

Sugar and salt.

Well done! Both sugar and salt are soluble in water to form a solution. Subsequent filtration cannot separate them from each other.

Hint

Iron filings, sulfur powder and sand are insoluble in water. Salt and sugar are soluble in water.

Q4. MRQ Which of the following statement(s) is/are true about distillation? (You may choose more than one answer.) 

Distillation is a separation technique used to separate a solid from a solid-liquid mixture.

That is incorrect. Distillation is used to separate a pure liquid from a solid-liquid mixture, or a liquid-liquid mixture.

 Distillation is a separation technique used to separate a pure liquid from a liquid-liquid mixture.

That's right! Distillation is used to separate a pure liquid from a solid-liquid mixture, or a liquid-liquid mixture.

The two main processes involved in distillation are boiling and condensation.

That's right! The main processes involved are boiling/evaporation and condensation.

Q5. MRQ Which of the following statement(s) is/are true about chromatography? (You may choose more than one answer.)

Chromatography is a separation technique used to separate a solid from a liquid-solid mixture only.

That is incorrect!Chromatography is used to separate small quantities of a liquid from a liquid-liquid mixture.

Chromatography can be used to separate small quantities of a liquid from a liquid-liquid mixture.

That is correct!Chromatography is used to separate small quantities of a liquid from a liquid-liquid mixture.

The more soluble a solute is in a solvent, the further it will travel on a chromatography paper.

That is correct!The more soluble a solute is in a solvent, the longer the distance it will travel on a chromatography paper.

Q1. FILL-IN-THE-BLANKS State the most appropriate separation technique for the following mixtures:

1. Obtain water from a mixture of sand and water

Distillation Water can be separated from sand by distillation.

2. Obtain salt from a beaker of salt solution

Evaporation

Evaporation can be done to remove the water, leaving the salt behind.

 

3. Obtain sand from a mixture of sand and water

Filtration

Filtration can be used to separate sand from water as sand does not dissolve in water.

4. Obtain iron filings from a mixture of iron filings and sand

Magnetic attraction

 

 

 

 Version:

1. https://vle.learning.moe.edu.sg/my-library/lesson/view/3b76fbcc-81a1-4e8d-8e09-33669130b837
2. https://sg.iwant2study.org/ospsg/index.php/interactive-resources/chemistry/01-experimental-chemistry/892-separation-techniques-lower-secondary-science
3. https://weelookang.blogspot.com/2019/08/separation-techniques.html

Other Resources

[text]