Practical: Elements, Compounds & Mixtures

Aims

1. To observe and compare the properties of compounds and mixtures made up of the same constituent elements.

2. Thus, infer some common characteristics of mixtures and compounds that can be used to distinguish them.

Procedure and Observations

Part A: Investigating a mixture of elements

1. Observe and record the appearance (colour and state) of some iron filings and sulfur powder:

Appearance of iron filings: black, solid (powder)

Appearance of sulfur power: yellow, solid (powder)

2. Observe and record the physical properties of mixture of iron and sulfur.

i. Place a spatula of iron filings and a spatula of sulfur powder on a piece of filter paper. Mix them together,

ii. To form a mixture, can the iron filings and sulfur be mixed in any proportion?

Observation: Yes they can be mixed in any proportion to form a mixture.

iii. Feel the mixture (from the bottom of the filter paper). Does it feel warm?

Observation: No

iv. Move a magnet under the filter paper. Does the magnet separate the mixture of elements?

Observation: Yes, the magnet separates the iron filings from the sulfur powder. The magnet attracts the iron filings, therefore separating the two elements.

v. Add iron and sulfur mixture into a text tube of water. Stir the mixture and then let it stand for a while. Draw and label what you see.

vi. Does water separate the mixture of elements?

Observation: Yes

vii. Do the iron filings and the sulfur act as separate substances or a single substance with water.

Observation: They act as separate substances.

Conclusions:

·      The substances in a mixture can be mixed in any proportion.

·      When a mixture is formed, heat and light are not usually taken in or given out.

·      The mixture can be separated by physical means.

·      The mixture has the properties of its constituent substances.

Part B: Mixture or Compound?

1. Mix one spatula of sulfur and half a spatula of iron filings in a crucible.

2. Cover the crucible with a lid and heat for 10 minutes using a strong flame.

Appearance of the residue after heating:

A black sold remained in the crucible. Before heating, the solid mixture was heterogeneous with specks of yellow and grey.

Does the magnet separate the residue into iron and sulfur?

No.

Add the residue to water. Stir and allow the mixture to stand. Draw and label what you see.

Conclusion: The residue formed is a compound. The elements can no longer be easily separated by physical methods and they lose their original properties – e.g. iron was no longer magnetic when it formed a compound).

Practical: Bunsen Burner

We went to the RGS Laboratory to learn about the different parts of the Bunsen burner, the purpose of each of the parts and how to light the Bunsen burner. After that, we also designed an experiment to find out the hottest part of the non-luminous flame from the Bunsen burner.

Activity 1: Naming the parts of the Bunsen burner

Functions

Air holes: To allow air to enter the burner (Oxygen is required for burning. Therefore the air hole is opened to allow the oxygen to enter, resulting in the burning of the gas to produce the flame.)

Barrel: (Where gas and air are mixed) To raise the flame to a suitable height for heating/burning

Base: To support the burner and make it more stable

Collar: To control the amount of air entering the burner (In other words, control the size of the air hole).

Gas Intake Tube: To allow the gas from the gas supply to rush into the burner.

Gas Tap: To control the amount of gas supplied to the burner.

Steps to light the Bunsen burner:

1. Attach the gas intake tube (rubber tube) to the gas tap.

2. Close the air hole by turning the collar.

3. Have the lighter ready; positioned at the top of the barrel

4. Turn the gas tap on completely and strike the lighter immediately and continuously until the burner is lit.

5. Turn the gas tap until the flame is about 5cm tall.

6. Turn the collar until the air hole is half opened.

Activity 2: Procedure of experiment to find out which part of the (Blue) Bunsen flame is hottest:

1. Light the Bunsen burner.

2. Adjust the air hole by turning the collar, to get a suitable non-luminous flame.

3. Use the metal tongs to hold one copper wire at the inner blue cone.

4. Hold the copper wire at the same position for 30 seconds.

5. Observe and record the changes in the copper wire.

6. Repeat steps 3, 4 and 5, holding the copper wire in the outer yellow cone instead.

Observations/Results

Conclusion: The tip of the inner blue cone is the hottest part of the Bunsen flame.

Classification & Elements, Compounds and Mixtures

Output - processing

Input (Directed Content)

Activity 1: We listed all the soft toys we had. We were then asked to classify them into groups. List Teddy bear  Dog  Rabbit  Giraffe Duck Sheep Monkey  Snake Elephant  Lion Hyena  Turtle Panda Hamster Polar bear Ponyo Totoro Carebears Shrek  Grizzly Bear Koala Angry Birds Mickey Mouse Doll Kangaroo Dolphin Pooh Eeyore Wombat Puppy Stitch  Penguin Piglet St. Bernard Ninja We classified these into 2 groups, “Animals that exist in real life” and “Fictional Characters”. This is our classification chart: Activity 2: We were given 12 different diagrams and were asked to classify them. We decided to classify them into 3 groups, “Elements”,  “Compounds” and “Mixtures”. This is our classification chart: Pre-reading of Elements, Compounds and Mixtures - My Notes Determining Purity A pure substance is made up of only one substances and is not mixed with any other substance. (e.g. white diamond) Important to determine purity as impurities in medicine may produce undesirable effects Important to ensure our food and drinks contain only chemicals that are safe for consumption - How to determine purity? A pure solid has an exact and constant (or fixed) melting point --> it will melt completely at one fixed temperature Impurities lower the melting point (more impurities --> lower the melting point) Impurities cause melting to take place over a range of temperatures A pure liquid has an exact and constant (or fixed) boiling point. Impurities increase the boiling point (more impurities --> higher the boiling point) Impurities cause the liquid to boil over a range of temperatures If the pressure acting on a liquid increases, the boiling point is also raised and vice versa.  Chromatography To test whether all the dyes in food colouring are safe for us to consume Chromatography is technique of using a solvent to separate its mixture into its components. (paper chromatography) Used to separate dyes in ink/pigments in plants/amino acids obtained from proteins to identify poisons or drugs, and to detect traces of banned substances in food 2 ways paper chromatography is carried out --> Add the solvent to make the substance spread out on circular chromatography paper, to form rings showing the different dyes the ink is made up of. --> Allow the solvent to ascend/travel up the chromatography paper The chromatography paper with the separated components is called a chromatogram. If there is only one spot on the chromatogram, it means the substance is pure. The ratio between the distance travelled by the substance and the distance travelled by the solvent - Rf value (constant as long as chromatography is carried out with the same solvent and at the same temperature) Rf value = distance travelled by the substance divided by distance travelled by solvent Identical dyes produce spots at the same height and in the same colour on the paper when the same solvent is used.  A locating agent is used to convert colourless chemicals into coloured chemicals that can be seen on the chromatogram.  Uses --> separate the components in a sample, identify the number of components in a sample, identify the components present in a sample and determine whether a sample is pure. Separation Techniques How to separate: (a) A solid from a liquid (b) Solids (c) A liquid from a solution (d) Liquids Decanting To separate a dense, insoluble solid from a liquid Process: Pouring the water away Filtration To separate small solid particles (sand, clay, dust particles and precipitates) from a liquid Process: 1. Fold the filter paper into quarters and open it up into a cone shape. 2. Line the filter funnel with the filter paper. 3. Pour the mixture into the filter funnel. 4. Collect the filtrate that passes through the filter paper, in a conical flask. 5. Wash the residue left in the filter paper with distilled water and leave it to dry on filter paper. The solid that remains on the filter paper is called residue. The liquid or solution that passes through the filter paper is called the filtrate. Evaporation to dryness To separate substances that dissolve in water by evaporating water from the solution. NOT a good method of purification for substances that decompose when heated strongly. When the water is removed, any soluble impurities present will also be left behind. Crystallisation To obtain a pure solid sample from its solution Process: 1. Water is removed by heating the solution until a hot saturated solution is formed. 2. When this resulting solution is allowed to cool to room temperature, the dissolved solid will be formed to pure crystals. How do we test for a saturated solution(can be produced by evaporation)? - Dip a clean glass rod into the solution. If the small amount of solution that sticks onto the rod forms into crystals as the solution cools, the solution is saturated. Dissolving and Filtration To separate a mixture where one substance is soluble and the other is insoluble in a solvent. Magnetism To separate magnetic materials from non-magnetic materials Magnets are used in recycling to recover magnetic materials from domestic waster. Sublimation To separate a substance that sublimes (e.g. ammonium chloride, iodine) from one with a high melting point (sand or sodium chloride). Simple Distillation To separate a pure solvent from a solution Process: Boiling the liquid and condensing the vapour. NOTE! - The thermometer should be placed beside the side arm of the distillation flask. This ensures that the thermometer measures the boiling point of the substance that is being distilled. Cold running water enters the condenser from the bottom and leaves form the top. The condenser slopes downwards. If the distillate it volatile, the receiver can be put in a large container filled with ice. This is to keep the temperature low and thus, maintain the distillate in its liquid state. Used to: - Recover a solvent from a non-volatile solute - Separate mixtures of liquids with different boiling points (BOILING POINTS WHICH DIFFER BY LESS THAN 20 DEGREES CELSIUS IS DIFFICULT TO BE SEPARATED BY SIMPLE DISTILLATION)  Separating Funnel To separate immiscible liquids (liquids that do not dissolve in each other - e.g. oil and water) Fractional Distillation To separare a solution of miscible liquids (e.g. ethanol and water) A fractionating column is attached to the round-bottomed flask and the condenser. Many glass beads (plates/a spiral) in the fractionating column provide a larger surface area for vapour to condense on. Process: - The liquid with the lowest boiling point will distil over to the condenser first. - The vapours of liquids with higher boiling points condense along the fractionating column and re-enter the round-bottomed flask.  Industrial applications of fractional distillation: Fractional distillation is used in industries to obtain nitrogen, argon and oxygen from air. Fractional distillation can be used to separate mixtures of liquids such as crude oil. Ethanol is formed when glycose solution undergoes fermentation in the presence of yeast. We can separate ethanol from glucose solution by fractional distillation.

·    Matter can be classified into elements, compounds and mixtures. ·    An element is a pure substance that cannot be split up into two or more simpler substances by chemical processes or by electricity. ·    Chemical changes (chemical reactions) –       -       Sugar -----> carbon + water (not easily reversed)       -       Melting of wax       -       Rusting ·    Physical changes       -       water (liquid) à water (gas) [easily reversed] ·    Compounds:       -       Formed by chemical reactions                    e.g. burning of magnesium in oxygen to form magnesium oxide       -       The properties of compounds are different from the properties of its constituent       -       Compounds have fixed compositions. (e.g.  water is always made of 11% oxygen and 89% hydrogen) ·      Breaking a compound:       -       By decomposition (thermal decomposition       -       By electrolysis          ·            The boiling point/melting point of a substance can be used to determine the purity of the substance. Naming elements      ·      Standardized internationally by IUPAC      ·      Some named after countries      ·      Names of Elements      ·      Names of elements in Latin      ·      Our body is made up of 26 elements        ·      Oxygen ·      Hydrogen ·      Carbon ·      Calcium ·      Nitrogen ·      Phosphorus ·      Other elements          ·            Element Song:            http://www.privatehand.com/flash/elements.html