Chemistry

1a) Explosives has helped mining (採礦), drilling, constructing tunnels.BUT explosives were widely used by the military in artillery (火炮) and bombing (轟炸) which has killed many people.

1b) Insecticides (殺蟲劑) kills bugs which would destroy crops. This increases agricultural (農業的) yield (產量). But insecticides pollute water sources when washed into rivers and into groundwater.

1c) Aspirin (亞士匹靈) is a painkiller (止痛藥) which also relieves angina (心絞痛). It is very cheap, but would cause stomach ulcers (胃潰瘍).

2a) Mushroom soup is a mixture of mushrooms and water and other flavourings like cream, salt, pepper etc.

2b) Sea water is a mixture of primarily water and dissolved salt. The salt is mostly sodium chloride and potassium chloride.

2c) Milk is a mixture of water, proteins, fat, minerals and vitamins.

2d) Distilled water is a pure substance, containing only water molecules水分子.

2e) Air is a mixture of gases, primarily nitrogen and oxygen gases. Also noble gases like argon and helium, carbon dioxide, water vapour and methane (甲烷).

3a) Eggs contain protein 蛋白質. Proteins are compounds of carbon, hydrogen, oxygen and nitrogen. The egg yolk蛋黃contains proteins and fat.

3b) Carbon dioxide is a compound of carbon and oxygen.

3c) Ice is purely water. But water H2O itself is a compound of hydrogen and oxygen.

3d) Iron is a pure element.

3e) Nitrogen is a pure element.

3f) Tricky one. Concrete is both a mixture and a compound. It is a mixture of water, cement英泥, limestone石灰and crushed rocks. When mixed up it looks like a liquid, but then they all react and becomes a solid.

4ia) Physical.
4ib) Melting or boiling points must be physical properties
4ic) Milk turns sour due to reaction with oxygen, or by micro-organisms微生物so chemical property.

唔夠位！另外找地方答。

2013-09-15 02:57:58 補充：
4iia) Compound. Carbon dioxide has 2 types of atoms: carbon and oxygen atoms so CO2 is NOT an element. The atoms are held by covalent bonds, but in a mixture the atoms are not held by any bonds.

4iib) Carbon melting point over 3000 degrees Celsius. Carbon dioxide has melting point of -76 degrees.

2013-09-15 03:00:23 補充：
4iic) Carbon dioxide forms white precipitates in limewater. Carbon does not react with limewater.

5) Exhale breath is NOT carbon dioxide: 78% nitrogen, 16% oxygen, 4% carbon dioxide etc.

5A Only copper atoms: pure substance.
5B A mixture of gases and can change with people. NOT pure substance.

2013-09-15 03:02:23 補充：
5C Soft drink: sugar, water etc. Different with factories. NOT pure substance.
5D White wine: 17% ethanol (乙醇酒精), the rest is water etc. Different with wine estates (酒莊). NOT a pure substance.

6a) Physical
6b) Chemical. Reaction with oxygen.
6c) Physical.
6d) Chemical. Reaction.

2013-09-15 03:02:50 補充：
7a) Physical.

7b) Chemical. Burning is a chemical reaction with oxygen. The reaction generates great heat and a dazzling white light which you can observe. The white powder is magnesium oxide. It is not shiny and does not conduct electricity.