COMPOUNDS AND MIXTURES

Important Definitions

solute	The substance that you dissolve. Eg salt
solvent	The liquid that you dissolve the substance in. Eg water
solution	The mixture formed when you dissolve a solute into a solvent
soluble	Able to dissolve in a solvent
insoluble	Unable to dissolve in solvent
dissolve	The process of mixing the solute with the solvent to give a clear solution
Dilute	Few particles of a solute are present in a given volume
concentrated	Lots of particles if a solute are present in a given volume of solvent
saturated	No more solvent can dissolve in the solvent

Filtration

Filtration separates soluble particles from insoluble particles ina solvent. If you have a mixture of two solids you can add water to dissolve one, filter off the insoluble one and then evaporate the water from the dissolved could to recrystallise the soluble solute.

Magnets

Magnets can be used on mixtures than contain iron or steel to remove the iron solid

Evaporation

- if you want to remove a solute that is dissolved in a solvent you can use evaporation. The solution is poured into an evaporating dish and heated. The solvent (often water) forms a gas and evaporates.

- It is important NOT to heat the solution to dryness as it will crack the dish. Stop heating when there is a little liquid left and the heat of the dish will continue to evaporate the liquid.

- You can also leave a solution in a shallow dish for a longer period of time at room temperature to evaporate

Distillation

Evaporation will separate a solid from a solvent if you only want to collect the solid.

If you want to collect the solvent as well or if you have two different liquids, then you should use distillation. Distillation separates substances on the basis of their boiling points.

Chromatography

Used to separate a mixture of coloured liquids such as inks. A small spot of the mixture is made on a piece of chromatography paper and the solvent is allowed to move up on the paper. Some inks travel faster than others go further. You can see if an ink is a mixture if one spot of colour moves. A mixture of inks will result in more than one spot.

Gas testing

Hydrogen h₂

- The first element on the periodic table

- the most abundant element int the universe and makes up 92% of the sun

- can make hydrogen in the lab by putting a metal (eg magnesium) into an acid

Magnesium + Hydrochloric acid -> magnesium chloride + hydrogen

- You will see bubbles forming. If you trap these bubbles and hold a lit splunt in the gas, you should hear a squeaky pop sound

7 Diatomic Elements

We call them diatomic elements because the atoms appear in pairs.

1. Hydrogen H-H

2. Nitrogen N=N

3. Oxygen O=O

4. Fluorine F-F

5. Chlorine Cl -Cl

6. Bromine Br - Br

7. Iodine I -I

2 - 7 Creates symbol 7 on periodic table

Oxygen O₂

Oxygen is a major part of the Earth's crust and is present in many everyday substances such as water and sugar. It is also important in combustion and respiration.

You can make oxygen in the lab by putting a pinch of maganese dioxide (a black powder) into hydrogen peroxide. You will see bubbles forming. If you trap these bubbles and hold a lit splint in the gas, the splint should relight - often many times.

Hydrogen Peroxide + Manganese Oxide -> Oxygen +Water

Carbon Dioxide CO₂

Carbon Dioxide is essential for life on Earth as plants take it in during photosynthesis. It is also used in some fire extinguishers as it doesn't support combustion and can be used as dry ice in smoke machines.

You can make carbon dioxide in the lab by adding acid to a metal carbonate solid or solution, eg calcium carbonate (marble chips). You will see bubbles forming. If you use a delivery tube to bubble this gas through lime water, the limewater should turn milky / cloudy.

Calcium carbonate + Hydro Chloric Acid -> Calcium Chloride + Carbon Dioxide + Water