c5 –chemicals of the q2 question explain why most molecular

QuestionName a gas in dry air that is a compound. Give the formula of this gas.

C5 – Chemicals of the natural environment

Q1

Answer:Carbon dioxide – CO

2

QuestionExplain why most molecular substances are gases.


Q2

Answer: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.

QuestionEthane can be represented by the molecular formula C

2H6. Draw a 2D

diagram of its structure.


Q4

Answer:

QuestionWhat is covalent bonding?


Q3

Answer:A covalent bond forms when two non-metal atoms share a pair of electrons.

SThaw 2014

QuestionWhat is the Earth’s hydrosphere?


Q5

Answer:The hydrosphere is the oceans.

QuestionWhat makes sea water salty?


Q6

Answer:The water contains dissolved ionic compounds, many of which are salts e.g. sodium chloride and magnesium chloride.

QuestionWhy do solid ionic compounds form crystals?


Q8

Answer:Ionic compounds are made of charged particles called ions. Ions with opposite charges are strongly attracted to each other and form a giant lattice.

QuestionDescribe how an ionic bond is formed.


Q7

Answer: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.

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QuestionDo solid ionic compounds have high or low boiling points? Explain why.


Q9

Answer: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.

QuestionWhy can ionic compounds conduct electricity when dissolved in water but not when they are solid?


Q10

Answer: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.

QuestionWhat is the test for carbon dioxide?


Q12

Answer:Bubble the gas through limewater. If the gas is carbon dioxide, the limewater will turn cloudy.

QuestionHow can you use the charges on ions to work out formulae?


Q11

Answer:The charges must cancel out to form a neutral compound.

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QuestionWhat is a precipitation reaction?


Q13

Answer:A solid forms when two solutions are mixed together,

QuestionWhen sodium chloride dissolves, which ions does it form?


Q14

Answer:Sodium Na+

Chloride Cl-

QuestionName three abundant elements in the Earth’s lithosphere.


Q16

Answer:SiliconOxygenAluminium

QuestionWhat is the Earth’s lithosphere?


Q15

Answer:The lithosphere is the rigid outer layer and is composed of a mixture of minerals.

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QuestionWhat property of diamond makes it suitable for its use in drill tips and precision cutting tools.


Q17

Answer:It is very hard.

QuestionExplain how the bonding in diamond makes it hard.


Q18

Answer:All the carbon atoms are bonded to each other by strong covalent bonds. This gives it a rigid structure.

QuestionWhat is an ore?


Q20

Answer:An ore is a rock that contains enough of a mineral (metal compound) for the metal to be extracted from it.

QuestionGraphite conducts electricity, which is unusual for a non-metal. Explain why it has this property.


Q19

Answer:Each carbon atom is bonded to three others, forming layers. There are also delocalised (free) electrons that can move freely.

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QuestionName a metal that can be extracted by reducing its oxide with carbon.


Q21

Answer:Zinc, Iron, Tin, Copper.Metals that are less reactive than carbon.

QuestionWhat is electrolysis?


Q22

Answer:The decomposition (breaking down) of a substance using electricity.

QuestionDescribe what happens at the electrodes during the electrolysis of molten aluminium oxide.


Q24

Answer: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.

QuestionWhy can a molten ionic crystal act as an electrolyte?


Q23

Answer:The ions are free to move.

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QuestionWhat do the terms reduced and oxidised mean?


Q25

Answer:Oxidation is loss of electrons.Reduction is gain of electrons.

OILRIG (Oxidation is loss, reduction is gain).

QuestionCalculate the relative formula mass for the following:a) MgCO

3

b) Na2CO

3


Q26

Answer:a) 24 + 12 + (3 x 16) = 84b) (2 x 23) + 12 + (3 x 16) = 106* Use relative atomic mass in periodic table

QuestionWhy are metals able to conduct electricity?


Q28

Answer:They have free electrons.

QuestionCalculate how much aluminium can be extracted from 400g of aluminium oxide.


Q27

Answer:Aluminium oxide = (27 x2) + (16 x3) = 102%mass of aluminium = [(27x2) ÷ 102] x 100 = 53%Mass of aluminium = (53÷100) x 400 = 212g

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QuestionWhy do metals have high melting and boiling points?


Q29

Answer: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

Answer: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.

QuestionGive the ion equations for the reactions at each electrode during the electrolysis of aluminium oxide.


Q32

Answer:At the negative electrode:Al3+ + 3e− → AlAt the positive electrode:2O2−

→ O2+ 4e−

QuestionGive two reasons why it is a good idea to recycle metals.


Q31

Answer:Saves energy.Better for the environment.Saves money.Conserves resources (ores are finite)Reduces landfill

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QuestionGive one impact on the environment for extracting metals.

c5 –chemicals of the q2 question explain why most molecular

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