Notes

Pure Substances
• always have a definite/constant composition
- 10 ml of water then fill up to 20 ml (both r 100% pure water)
- i can change the quantity but not the composition
- even though i filled it, its still 100% pure water
- the only way to change its composition is to make it a mixture (ex: adding salt to the water)
• can be elements or compounds
• individual molecule/atom, pure element, or single type of compound
• examples:
- Helium (He) - single element is always pure substance and composed of singular atoms
- Hydrogen gas (H2) - (molecule and pure element- made up of one type on atom) (only made of one type of atom - hydrogen) pure element but composed of molecules- substance that has 2/more different/same atoms, if there are different atoms, its a compound
- sugar
- 24 karat gold (pure gold, gold is an element, so its a pure substance)
- Silver metal (silver - pure element = pure substance)
• Compounds (single compound - pure substance)
- made up of 2 or more diff atoms
- ex: H20 (molecule) (made up of two different atoms which makes it also a molecule)
• u can seperate by chemical methods
if u take a beaker, add water, and add two metal electrons and take a nine volt battery and connect it to the electrons, since water doesnt conduct electricity well, you'll need to add table salt to it for it to conduct electricity a lot better and bubbles will bubble up which are H2 and another set of bubbles which are O2- (electrolysis - chemical process that can break down water into its component elements (ex: H2 + O2))

Mixture
• mixture/combination of different pure substances
• has variable composition
- 5g salt and 95g water = 5% salt solution (can vary)
- 10g salt and 90 g water = 10% salt solution (can vary)
- i can control composition of my mixture
• ex:
- beaker w Hydrogen and Helium gas (H2 + He)
- Nitrogen and Oxygen gas (N2 + O2)
- Salt water (H20 + NaCl)
- brass (alloy- something composed of many metals, solid solution of copper and zinc)
- air (homogenous mixture of gases)
- sugar water - mixture of sugar and water
- 14 karat gold (mixture, alloy, some gold in it but theres also something else like silver/copper/etc)
- rubbing alcohol (composed of isopropyl alcohol and some water, example - 70% alcohol, the other 30% is water)
- soda (contains water, sugar, probably some caffeine)
- milk (has water, proteins, fat molecules, fatty acids, has multiple substances)
- sterling silver (alloy, solid solution of 92.5% silver and 7.5% copper)
- sea water (practically salt water, maybe w some other elements too)
- wood (comes from nature like trees and things like these are usually composed of carbs, proteins, nucleic acids, it doesnt consist of 1 type of compound/pure element)
- soil (could have some sand, etc, can be wet soil too)
- wine (water + alcohol)
• u can seperate components by physical methods
- ex: imagine beaker w water and salt, if u add heat to this, all the water molecules will boil off and there will only be table salt (NaCl) left because its very difficult to boil this off
- u can use physical process to seperate these^
- if you left a puddle of salt water in a dry room without any temp change, the water will evaporate by itself (evaporation - something that can evaporate without the use of heat)
• alloy - always a mixture