C5 Chemicals of the natural environment. C5 Chemicals of the natural environment

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Brandon Stewart
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1 Q1 Name a gas in dry air that is a compound. Give the formula of this gas. Carbon dioxide CO 2 Q2 Explain why most molecular substances are gases. The forces of attraction between molecules are weak. It does not take much energy to overcome these forces, so these molecular substances have low melting and boiling points. Q3 What is covalent bonding? A covalent bond forms when two nonmetal atoms share a pair of electrons. Q4 Ethane can be represented by the molecular formula C 2 H 6. Draw a 2D diagram of its structure.

2 Q5 What is the Earth s hydrosphere? Q6 What makes sea water salty? The hydrosphere is the oceans. The water contains dissolved ionic compounds, many of which are salts e.g. sodium chloride and magnesium chloride. Q7 Describe how an ionic bond is formed. When a metal reacts with a non-metal, electrons are transferred from the metal to the non-metal, forming ions. The strong electrostatic force of attraction between oppositely charged ions is called an ionic bond. Q8 Why do solid ionic compounds form crystals? Ionic compounds are made of charged particles called ions. Ions with opposite charges are strongly attracted to each other and form a giant lattice.

3 Q9 Do solid ionic compounds have high or low boiling points? Explain why. They have high boiling points. The forces of attraction between ions are very strong. It takes a lot of energy to overcome these forces and melt the compound and even more to make it boil. Q10 Why can ionic compounds conduct electricity when dissolved in water but not when they are solid? When an ionic compound dissolves, the ions separate and are free to move in the solution. This means that they can carry an electric current. In a solid, the ions are held firmly in place and cannot move. Q11 How can you use the charges on ions to work out formulae? The charges must cancel out to form a neutral compound. Q12 What is the test for carbon dioxide? Bubble the gas through limewater. If the gas is carbon dioxide, the limewater will turn cloudy.

4 Q13 What is a precipitation reaction? Q14 When sodium chloride dissolves, which ions does it form? A solid forms when two solutions are mixed together, Sodium Na + Chloride Cl - Q15 What is the Earth s lithosphere? The lithosphere is the rigid outer layer and is composed of a mixture of minerals. Q16 Name three abundant elements in the Earth s lithosphere. Silicon Oxygen Aluminium

5 Q17 What property of diamond makes it suitable for its use in drill tips and precision cutting tools. It is very hard. Q18 Explain how the bonding in diamond makes it hard. All the carbon atoms are bonded to each other by strong covalent bonds. This gives it a rigid structure. Q19 Graphite conducts electricity, which is unusual for a non-metal. Explain why it has this property. Each carbon atom is bonded to three others, forming layers. There are also delocalised (free) electrons that can move freely. Q20 What is an ore? An ore is a rock that contains enough of a mineral (metal compound) for the metal to be extracted from it.

6 Q21 Name a metal that can be extracted by reducing its oxide with carbon. Q22 What is electrolysis? Zinc, Iron, Tin, Copper. Metals that are less reactive than carbon. The decomposition (breaking down) of a substance using electricity. Q23 Why can a molten ionic crystal act as an electrolyte? The ions are free to move. Q24 Describe what happens at the electrodes during the electrolysis of molten aluminium oxide. Aluminium forms positive ions, so they are attracted to the negative electrode. The ions gain electrons and aluminium is formed. Oxide ions are negative, they are attracted to the positive electrode. The oxide ions lose electrons and oxygen is produced.

7 Q25 What do the terms reduced and oxidised mean? Oxidation is loss of electrons. Reduction is gain of electrons. OILRIG (Oxidation is loss, reduction is gain). Q26 Calculate the relative formula mass for the following: a) MgCO 3 b) Na 2 CO 3 a) (3 x 16) = 84 b) (2 x 23) (3 x 16) = 106 * Use relative atomic mass in periodic table Q27 Calculate how much aluminium can be extracted from 400g of aluminium oxide. Aluminium oxide = (27 x2) + (16 x3) = 102 %mass of aluminium = [(27x2) 102] x 100 = 53% Mass of aluminium = (53 100) x 400 = 212g Q28 Why are metals able to conduct electricity? They have free electrons.

8 Q29 Why do metals have high melting and boiling points? Metallic bonds are very strong. There is a strong electrostatic attraction between the positive ions and the electrons. It takes a lot of energy to separate them. Q30 Give one impact on the environment for extracting metals. Uses lots of energy. Scars the landscape. Destroys habitats. Noise/dust pollution caused by an increase in traffic. Deep mine shafts can be dangerous long after the mine has been abandoned. Q31 Give two reasons why it is a good idea to recycle metals. Saves energy. Better for the environment. Saves money. Conserves resources (ores are finite) Reduces landfill Q32 Give the ion equations for the reactions at each electrode during the electrolysis of aluminium oxide. At the negative electrode: Al e Al At the positive electrode: 2O 2 O 2 + 4e

WRITING CHEMICAL FORMULA

WRITING CHEMICAL FORMULA For ionic compounds, the chemical formula must be worked out. You will no longer have the list of ions in the exam (like at GCSE). Instead you must learn some and work out others.