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66 Cards in this Set
- Front
- Back
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What does fluorine look like at room temperature? |
Pale yellow gas |
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What does chlorine look like at room temperature?
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Yellow-green gas |
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What does bromine look like at room temperature?
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Dark red-brown liquid |
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What does iodine look like at room temperature?
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Grey-black solid |
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What does astatine look like at room temperature?
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Black solid |
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What is the bonding and structure of halogens? |
They have covalent bonds within atoms and are found as diatomic molecules. They have induced dipole-dipole forces between molecules and a simple covalent structure |
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How many electrons are in their outer shell? |
7 |
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What block of the periodic table are they in and why? |
P block as their outermost electron is in a P orbital. |
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What charge do molecules have and why? |
They're non-polar as electrons are shared equally |
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Why do halogens have low mp and bps? |
Little energy is needed to break weak London forces between molecules |
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What happens to mp and bp as you go down the group? |
They increase. This is because, as you go down there are more shells, so there are more electrons. This means there are more/ stronger London forces between molecules |
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What type of reactant are halogens? |
They're powerful oxidising agents. |
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Why is it an oxidising agent? |
It removes electrons from reactions and gets reduced itself |
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What is the oxidising power of a halogen? |
A measure of the strength with which a halogen atom is able to attract and capture an electron to form a halide ion. |
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What happens to a halogen atom in a reaction? |
It gains one electron |
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Demonstrate this using chlorine? |
0.5Cl2 + e- ---> Cl- |
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What happens to the oxidation number of a halogen when it is involved in a reaction? |
It decreases from 0 to -1 as it's reduced |
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What's the difference between chlorine and chloride? |
Chlorine is a halogen molecule with an oxidation number of 0, whereas chloride is a halide ion with an oxidation number of -1. |
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How does reactivity change down the group? |
As you go down the group, reactivity decreases. |
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Why does reactivity decrease down the group? |
Electron shielding and atomic radius increases, which decreases nuclear attraction. This outweighs the increase in nuclear charge. This means that as you go down, the nucleus is less able to attract and capture another electron. |
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Which is the most reactive halogen and what does this mean? |
Fluorine, this means it's rarely found in its element form. |
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Which is the least reactive halogen? |
Astatine |
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What also decreases down the group for the same reasons? |
The strength of the oxidising agent. |
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What type of reaction are displacement reactions? |
Redox reactions |
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What does a displacement show? |
The decrease in reactivity (oxidising power) down the group. |
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What is a displacement reaction? |
A reaction in which a more reactive element displaces a less reactive element from an aqueous solution of a halide ion. |
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What two substances can halides be dissolved in? |
Water an organic solvents |
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What's the method to test for different halides? |
Each halogen solution is added to aqueous solutions of different halides (Cl-,I- and Br-) and the mixture is shaken. |
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What is the colour of chlorine dissolved in water and an organic solvent? |
Pale-green in both |
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What is the colour of bromine dissolved in water and an organic solvent?
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Orange in both |
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What is the colour of iodine dissolved in water and an organic solvent? |
Brown in water Purple in an organic solvent |
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Why is an organic solvent used to test for halogens? |
It produces colours which are easier to distinguish than those produced by dissolving the halogen in water. |
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What do aqueous halides form? |
Colourless solutions. |
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What would the redox equation between aqueous bromine and sodium iodide be? |
Br2 (aq) + 2NaI (aq) --> 2NaBr (aq) + I2 (aq) |
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What would the ionic half equations between aqueous bromine and sodium iodide be?
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Br2 + 2e- -->2Br- 2I- -->I2 + 2e- Bromine steals electrons from iodine |
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What would the overall ionic equation between aqueous bromine and sodium iodide be? |
Br2 + 2I- ---> 2Br- +I2 |
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What would the observation between aqueous bromine and sodium iodide be?
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The solution would go from orange to brown as iodine is displaced. |
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What is a disproportionation reaction? |
A reaction in which the same element is both oxidised and reduced. |
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What is one of the main disproportionation reactions involving chlorine? |
Chlorine and water |
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What is the equation for the reaction between chlorine and water? |
Cl2 (aq) + H2O (l) --> HCl (aq) + HClO (aq) |
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What products are formed? |
Hydrochloric acid and chloric (I) acid. |
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What is this mixture known as? |
Chlorine water |
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Why is this a disproportionation reaction? |
Chlorine is reduced as its ON decreases from 0 in Cl2 to -1 in HCl. It is also oxidised as its ON increases from 0 in Cl2 to +1 in HClO. |
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What can chloric acid form? |
H+ and ClO- (chlorate) ions |
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What is this reaction used for? |
To kill bacteria in the treatment of water as small amounts of chlorine are added to water to kill bacteria, |
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Which is the active ingredient which kills bacteria? |
ClO- ions |
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Where is this used? |
In swimming pools and drinking water |
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What test can be used to test for Chlorine water? |
Blue litmus paper can be used. It turns red and is then bleached white by HClO. |
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When was chlorine added to drinking water? |
The late 1890s. |
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What did this do? |
Some claim this improved public health. |
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What are concerns with this process? |
Chlorine is a toxic gas and environmentalists are worried that if this mixes with organic matter it may form chlorinated hydrocarbons. They are suspected carcinogens. |
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What did this cause in 1 country? |
In 1991, Peru stopped adding chlorine to water. This resulted in unsafe drinking water and caused an outbreak of cholera. This affected 1 million people and killed 10,000. The government then reversed their decision and resumed adding chlorine to their drinking water. |
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What is another disproportionation reaction involving chlorine? |
The disproportionation of chlorine in cold and dilute aqueous sodium hydroxide. |
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What is the equation for this reaction? |
Cl2 (aq) + 2NaOH (aq) --> NaCl (aq) + NaClO (aq) +H2O (l) |
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What are the products formed? |
Sodium chlorine, water and sodium chlorate (I) |
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Why is this a disproportionation reaction? |
Chlorine is reduced as its ON decreases from 0 in Cl2 to -1 in NaCl. It's also oxidised as its ON increases from 0 in Cl2 to +1 in NaClO. |
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Why is this an important reaction? |
It's used to make household bleach. The active ingredient is ClO-, the chlorate ion. |
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How do you test for different halide ions? |
Add dilute nitric acid and then aqueous silver nitrate solution until a precipitate forms. |
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What are the colours of the different precipitates? |
Cl- = white Br-= cream I- = yellow |
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What can be done after this? |
Further tests can be done as it may be difficult to distinguish between the colours. |
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What is done first? |
Dilute ammonia solution is added. |
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What happens when this is done? |
The chloride precipitate dissolves. The others remain |
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What is done next? |
Concentrated ammonia solution is added |
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What happens when this is added? |
Chloride and bromide precipitates dissolve. The iodide precipitate remains. |
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What is the equation for the reaction between chlorine and cold dilute sodium hydroxide solution? |
2NaOH + Cl2 --> NaCl + NaClO + H2O |
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What is the equation for the reaction between chlorine and hot, concentrated sodium hydroxide solution? |
6NaOH + 3Cl2 --> 5NaCl + NaClO3 + 3H2O |
