chemical changes sec 2

What is a physical change?

A change in which no new substances are formed. It can usually be reversed. (dissolving, evaporation)

What is a chemical change?

A change in which new substances are formed. It usually cannot be reversed easily.

How can you tell that there has been a chemical change?

Change in colour, change in temperature, production of gas and production of solid

What are the four types of chemical changes?

Combustion, thermal decomposition, oxidation, neutralisation

Define an acid

An acid is a substance that dissolves and dissociates in water to produce hydrogen (H+) ions and the corresponding negative ions.

Define a base

A base is a substance that reacts with an acid to produce salt and water only. They are usually metal oxides or hydroxides.

Define an alkali

An alkali is a substance that dissolves and dissociates in water to produce hydroxide (OH-) ions and the corresponding positive metal ions.

What are the three acid reactions?

Acids react with bases to form salt and water, with reactive metals to form salt and hydrogen gas, and with carbonates to form salt, carbon dioxide and water.

What are some unreactive metals?

Copper, silver and gold

What are the three tests for gases?

If the moist red litmus paper turns blue, ammonia is present. If the lighted wooden splint is extinguished with a pop sound when it enters the test tube, hydrogen is present. If, when the gas is bubbled into limewater, a white precipitate is formed, carbon dioxide is present.