Chemical and Physical Changes, Identifying Gases

• A physical change is when a substance changes form but can revert to its original state, like melting sugar.
• Water freezing into ice is a physical change.
• Lighting a match involves a chemical change.
• Oxygen is required for combustion.
• Water forms through a chemical reaction between oxygen and hydrogen gas.

Identifying Gases

• Oxygen can be identified by inserting a glowing splint into the gas; if the splint re-ignites, the gas is oxygen.
• Hydrogen can be identified by its reaction with oxygen; if the lit gas reacts violently with air's oxygen, creating water, it is hydrogen gas.
• Carbon dioxide can be identified by mixing it with limewater, if the limewater turns cloudy, the gas is carbon dioxide.

Elements and Compounds

• Helium is used in balloons because it is the second lightest gas.
• Knallgas is a mixture of hydrogen and oxygen
• Oxygen is always present in an oxide
• Iron nails are galvanized to prevent rust; aluminium is used as a thin layer.
• Zinc is the substance on the outside of a galvanized iron nail.
• Aluminium is preferred over iron for making soda cans due to its greater resistance to corrosion.

Chemical Properties and Uses

• Sparklers contain iron filings that create sparks when burned.
• Toothpaste is often slightly basic to help neutralize acids produced from food.
• BTB can be used as an indicator for pH values.
• Hydrogen ions are abundant in acidic solutions.
• Acids are useful for preserving food and in the production of batteries and fertilizers.
• Acetic acid preserves food by inhibiting bacteria and mold growth.
• Lactic acid in filmjölk and yogurt inhibits the growth of other bacteria.

Fire and Combustion

• The fire triangle consists of heat, oxygen and fuel, all needed for a fire to start.
• Fire is controlled, while a blaze is not.
• Flames form when gases from decomposing cellulose in burning paper react with oxygen, releasing energy in the form of light and heat.
• Gasoline is highly flammable due to its low flash point of -40 degrees.
• Gaseous fuels need to be handled carefully due to their flammability; they can ignite upon contact with an ignitable source.
• Blowing on glowing embers can cause them to flame up, as the added oxygen heats up carbon particles, which produces flames.
• Rapid combustion is called an explosion with the result of massive energy being released.

Fire Extinguishing Methods

• Blowing out a candle extinguishes the flame by removing heat from the candle's wax.
• Smothering a fire deprives it of oxygen.
• Carbon dioxide is a common extinguishing agent.
• A firebreak involves creating a barrier to prevent a fire from spreading.
• To extinguish a grease fire in a pot, cover the pot with a lid to smother the fire and turn off the heat, avoid using water.
• Before extinguishing a fire in an electrical appliance like a TV, unplug it and smother it with a fire blanket.

Chemical Formulas and Ions

• Hydrochloric acid: HCl
• Nitric acid: HNO3
• Sulphuric acid: H2SO4
• Hydrochloric acid: H+ hydrogen ions and Cl- chloride ions
• Nitric acid: H+ hydrogen ions and NO3- nitrate ions
• Sulphuric acid: H+ hydrogen ions and SO4-2 sulphate ions