1. Mixtures MATTER Chapter 7

2. MIXTURES A MIXTURE is a substance which is made up of the ATOMS of TWO (or more) ELEMENTS or the molecules of TWO (or more) COMPOUNDS which have NOT been JOINED TOGETHER IN A CHEMICAL REACTION. Mixtures are easy to SEPARATE and the COMPOSITION of a mixture can vary. However in a COMPOUND the atoms are CHEMICALLY combined. A definition of a Mixture

3. If we take, as an example, IRON and SULPHUR.

4. Examples of Mixtures AIR is a mixture of many different gases. It is dominated by two gases NITROGEN which makes up nearly 4 / 5 th of it and OXYGEN which makes up the other 1 / 5 th. There is also a small amount of ARGON and a very small amount of CARBON DIOXIDE. 1.AIR

5. SEA WATER is a mixture of solids, liquids and gases. It is mainly made up of WATER and dissolved SALT with very small amounts of OTHER COMPOUNDS. 2.SEA WATER

6. Types of Mixtures If you pass the school canteen close to lunch time you can’t fail to smell the delicious aroma of the food being prepared. Particles of GAS given off by food spread out and MIX with AIR particles. You can’t see these particles but you can SMELL them. This effect is known as DIFFUSION. Diffusion

7. Diffusion and gas pressure Diffusion occurs when TWO DIFFERENT GASES (or LIQUIDS) MIX TOGETHER so that the CONCENTRATION of the TWO GASES (or LIQUIDS) eventually becomes the SAME THROUGHOUT. This happens because of the degree of movement of the particles. It doesn’t happen in SOLIDS.

8. Diffusion in gases can be demonstrated by taking two jars of gas, one containing OXYGEN and the other BROMINE, a brownish gas. To begin with the two gases are separated from each other.

9. What has actually happened in the two jars can be explained using PARTICLE THEORY. The same effect can be seen using LIQUIDS. This takes longer because liquid particles move around more slowly compared to gas particles.

10. Air is a mixture of several gases and when a ball is INFLATED with air many millions of TINY GAS PARTICLES enter the ball. Once inside, the gas particles CONSTANTLY HIT the inside surface of the ball since they are MOVING AROUND VERY QUICKLY in ALL DIRECTIONS. GAS PRESSURE This constant hitting of the inside of the surface creates GAS PRESSURE.

11. SOLUTIONS When we add a SOLUTE i.e. a SOLID to a SOLVENT (i.e. a Liquid) and the SOLUTE DISSOLVES, the resulting mixture is called a SOLUTION. The SOLUBILITY of a SOLUTE in a SOLVENT is a measure of how much solute dissolves in the solvent. Solubility depends on many factors.

12. 1.TEMPERATURE OF THE SOLVENT The HIGHER the TEMPERATURE of the SOLVENT the GREATER the MASS of SOLUTE that dissolves. In other words, SOLUBILITY INCREASES WITH TEMPERATURE. This can be shown by adding equal masses of instant coffee to equal volumes of water at different temperatures.

13. 2.MASS OF SOLUTE ADDED There is a LIMIT to the MASS of SOLUTE which dissolves in a particular VOLUME of SOLVENT. Again this can be shown by adding different masses of instant coffee to EQUAL VOLUMES OF WATER AT THE SAME TEMPERATURE. As you can see a POINT IS REACHED where the coffee no longer DISSOLVES, no matter how long it is stirred. We now have a SATURATED SOLUTION.

14. A SOLUTE that dissolves in ONE PARTICULAR SOLVENT may NOT DISSOLVE in ANOTHER SOLVENT. This is why car mechanics use PARAFFIN-BASED CLEANERS rather than water to remove oil. 3.TYPE OF SOLVENT USED

15. ONE IMPORTANT NOTE During the formation of a solution the MASS OF THE SOLUTION FORMED is EQUAL TO THE TOTAL MASS of the SOLUTE and SOLVENT used. Forming a solution is an example of a PHYSICAL CHANGE taking place.

16. SEPERATING MIXTURES The substances which make up a mixture can be SEPARATED from each other if necessary. The following methods will cover most possibilities. 1.FILTRATION 2.EVAPORATION 3.DISTILLATION 4.CHROMATOGRAPHY The first three are the most important ones.

17. FILTRATION is used to separate an INSOLUBLE SOLID FROM A LIQUID. e.g. a mixture of CHALK and WATER. 1.FILTRATION

18. EVAPORATION is used to separate a SOLUBLE SOLID FROM A LIQUID when we want to COLLECT THE SOLID. e.g. a mixture of DISSOLVED SUGAR and WATER. 2.EVAPORATION THE SLOWER THE WATER IS EVAPORATED… THE BIGGER THE CRYSTALS.

19. DISTILLATION is used to separate a LIQUID FROM ANY SOLIDS WHICH ARE DISSOLVED IN IT in order to collect the liquid. e.g. If we wanted to produce PURE WATER from SEAWATER. 3.DISTILLATION The SALT WATER (sea water) SOLUTION IS BOILED… and WATER turns to STEAM… Which RISES UP THE FLASK… LEAVING SALT BEHIND. STEAM (VAPOUR) PASSES THROUGH THE TUBING… and REACHES THE COLD SURFACE of THE CONDENSER… where it CONDENSES back to WATER.

20. The above method can also be used to separate a MIXTURE of TWO LIQUIDS which have DIFFERENT BOILING POINTS, e.g. a mixture of ALCOHOL and WATER. The ALCOHOL BOILS FIRST (alcohol boils at about 78 o C) and its VAPOUR is CONDENSED BACK INTO PURE ALCOHOL. The WATER is LEFT BEHIND in the FLASK.

21. Chromatography is a method for analysing complex mixtures (such as ink) by separating them into the chemicals from which they are made. Chromatography is used to separate and identify all sorts of substances in police work. Drugs from narcotics to aspirin can be identified in urine and blood samples, often with the aid of chromatography. There exists various types of Chromatography but for this year it is interesting to know how one of these test work. 4. Chromatography

22. Paper Chromatography Materials Paper coffee filters One black permanent pen Black water soluble pens Container full of water Several sheets of paper Small glasses or plastic containers Isopropyl rubbing alcohol* Pencils Tape Scissors Stapler

23. Paper Chromatography Instructions 1. Cut several coffee filters into long strips, one strip per pen. 2. Fold the end of each strip over then staple it to form a loop. 3. Place a dot of ink near the bottom of each strip. Use a pencil to identify which strip belongs to which pen.

24. Paper Chromatography Instructions 4. Poke a pencil through one of the loops you just made. Use the pencil to suspend the strip in a small glass or container. 5. Carefully add water to the glass until it reaches the bottom of the paper strip just below the ink dot. Be sure the ink stays above the water and the paper stays in the water. 6. Allow the water to soak up the strip and watch what happens to the ink drop. 7. If the ink you are testing does not spread out, re-test it using rubbing alcohol. 8. Repeat this process for each strip and compare your results. 9. Let the strips dry and tape them on a sheet of paper as a record of the different pen types.

25. Paper Chromatography What’s happening Because molecules in ink and other mixtures have different characteristics (such as size and solubility), they travel at different speeds when pulled along a piece of paper by a solvent (in this case, water). For example, black ink contains several colours. When the water flows through a word written in black, the molecules of each one of the colours behave differently, resulting in a sort of “rainbow” effect. Many common inks are water soluble and spread apart into the component dyes using water as a solvent. If the ink you are testing does not spread out using water, it may be “permanent” ink. In such cases, you will have to use a different solvent such as rubbing alcohol.