Chemistry - Mixtures

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  • Created by: Qian Ru
  • Created on: 09-09-13 01:28
What is bronze made up of?
Tin and copper.
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What is brass made up of?
Copper and zinc.
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Why do we need to separate mixtures?
To remove impurities, e.g. during water treatment.
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Why do we need to separate mixtures?
To obtain useful substances from mixture.
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Why do we need to separate mixtures?
To find out the type of substances that make up the mixtures, e.g. the types of colour pigments present in the black ink.
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State the types of separation techniques.
Magnetic attraction, filtration, evaporation, crystallisation, separating funnel, sublimation, simple distillation, fractional distillation and chromatography.
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What is meant by physical method?
This means that the substances in the mixture are simply separated from one another; they do not change into other substances or undergo any chemical reactions.
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What is magnetic attraction?
It is a physical method for separating magnetic substances from non-magnetic substances.
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How does magnetic attraction work?
The magnetic substances will be attracted to the magnet while the non-magnetic substances will not.
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How is magnetic attraction applied in daily life?
Separation of iron from scrape metals.
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What is filtration?
It is a physical method used for separating insoluble solids from a liquid in a mixture.
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How does filtration work?
Filter paper contains very small holes/pores which allow the liquid particles ti pass through but not the larger insoluble particles.
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How is filtration applied in daily life?
Filtration units in fish tanks, dust filters and the extraction of sugar from sugar cane.
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In filtration, what are some of the substances?
Residue and filtrate.
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What is evaporation?
It is a physical method for separating dissolved solids from a solution.
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How does evaporation work?
All the solvent in the solution will be evaporated, leaving the solute in the evaporating dish.
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Why can't we use filtration instead of evaporation.
Sometimes, the solute may have already dissolved in the solution and is now small enough to pass through the pores of the filter paper.
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Why is the evaporating dish not heated directly over the Bunsen flame?
For more even heat distribution as the salt solution is heated by steam from the boiling water bath.
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What happens to the salt solution during evaporation?
During evaporation, water boils and changes into steam. Salt is left behind as the residue.
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When evaporating salt solution, why does the salt not boil off too?
This is because salt has a much higher boiling point than water.
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How is evaporation applied in daily life?
Obtaining salt from sea-water, drying wet clothes in the sun, water evaporating from the road and Sweat evaporating from the body.
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What happens when sweat evaporates from the body?
It gains heat from your body and evaporates, taking the heat away from your body, which makes you cooler.
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What is crystallisation?
It is a physical method for separating dissolved solids from a solution which decomposes on heating.
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How does crystallisation work?
The impure solid is dissolved in a solvent. The solution is then heated to evaporate most of the solvent. The hot solution is allowed to cool. The solid appears as pure crystals. The cold solution is poured off to obtain the crystals.
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What is sublimation?
It is a method used to separate a substance that sublimes from one with a high melting point.
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What are some examples of substances that sublimes?
Iodine, ammonium chloride and dry ice.
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What are some examples of substances with a high melting point?
Sand and sodium chloride.
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How does sublimation work?
Firstly, the substance that sublimes would evaporate to form vapour. Then it touches a cooler surface and condenses into a solid. Solidified (iodine) would then be separated from a substance with a high melting point.
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What is separating funnel?
It is used to separate liquids that do not mix. A separating funnel is used to separate two immiscible liquids of different densities.
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How does separating funnel work?
The mixture is placed in a separating funnel. Leave the mixture till the liquids separate into 2 distinct layers. The denser liquid is found on the bottom of the funnel. The denser liquid is removed from the bottom of the funnel into a receiver.
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What is simple distillation?
It is a physical method for separating the solvent from a solution.
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What processes does simple distillation involves?
Boiling and condensation.
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How does simple distillation work?
The solution in the distilling flask is heated until it is boiled. (Salt) remains in the flask as it has a higher boiling point. When (water) boils, it changes into steam. The steam cools down and changes into liquid when it reaches the condenser.
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What is the use of the porcelain chips in simple distillation?
To ensure smooth boiling as it prevents intense boiling.
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Why is the thermometer placed at the top right part of the distilling flask?
To measure the boiling point of the solvent that is being distilled over.
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Why does the tap water comes in at the top and out at the bottom in the condenser?
When water enters from the bottom, it forces the water to go against gravity so it moves slower, that way, it is more efficient as a condenser.
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What is the use of the condenser?
To ensure full circulation of water to cool and condense the vapour in the condenser efficiently, such that no vapour can escape uncondensed.
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Why should the receiver be put with a large amount of ice?
A the distillate is volatile, it helps to keep the temperature of the distillate low so that it remains in its liquid state.
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Why should there not be any stopper at the receiver?
Pressure will biuld up and the flask will crack, or the distillate will not be fully collected as air in the conical flask is not displaced out.
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How is simple distillation applied in daily life?
Distillation is used to produce pure water.
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What is fractional distillation?
It is a physical method used for separating a mixture of two or more miscible liquids which have different boiling points.
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How does fractional distillation work?
The liquid with a higher boiling point tends to condense first. The liquid with lower boiling point moves further up the column. The liquid with a lower boiling point would distill over first, which effectively separates the two liquids.
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Why does the liquid with higher boiling point condense first in fractional distillation?
The liquid with a higher boiling point needs more energy to evaporate and move up compared to a liquid with low boiling point. So when there is not enough energy for the liquid with higher boiling point, it will condense faster.
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How is fractional distillation applied in daily life?
It is used in oil refineries to separate petroleum into products such as petrol, kerosene and diesel fuel.
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What is chromatography?
It is a technique of separating components of a mixture as it is carried by a solvent or gas over the surface of a material.
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What are the principles of chromatography?
Different substances have different solubility in the same solvent. The more soluble substance will dissolve faster into the solvent and move further ahead of the less soluble solutes.
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What is the filter paper called in chromatography?
Chromatogram.
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How does different solubilities supports chromatography?
The difference in solubilities allows the pigments in the dyes to be separated.The more soluble ones move up the paper; while others that do not dissolve much in the solvent, is trapped and so does not travel very far up in the paper
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What are the procedures of chromatography?
Spots of the mixture or analytes are placed along a baseline drawn by pencil.The end of the paper closer to where the spots are located is dipped into a pool of solvent.The solvent would travel to the end of the paper.It would be removed and analysed
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Why is the analyte of chromatography marked with pencil?
It serves as a suitable marker as it does not dissolve in most solvent and does not interfere with the spots.
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Why must the spots be small? (Chromatography)
They will interfere with other spots and become unclear.
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Where should the start line be in chromatography?
It should be above the level of the solvent otherwise the sample will dissolve in the solvent and not be separated out.
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What is the edge of the solvent level called in chromatography?
Solvent front.
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What is the analysis of chromatogrphy based on?
It is based on retention factor.
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How can the retention factor be calculated in chromatography?
It can be calculated from the distance traveled by the solvent and the mixture or analytes.
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What analysis can be found from chromatography?
Distance moved by analyte (DA) and distance moved by solvent (DS)
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What is used to separate an insoluble substance from a liquid?
Filtration.
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What is used to separate a solid from a solution?
Evaporation.
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What is used to separate a liquid from a solution?
Fractional/Simple distillation.
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What is used to separate a mixture of coloured substances.
Chromatography.
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