This compartmentalised document contains complete, thorough notes on the halogens (Group 7) and can also act as a "test yourself" resource by covering up certain parts. I use exam vocabulary in my document but it's still easy to follow. These notes are arranged in bullet points, making it clear whe...
A student adds a small volume of aqueous silver nitrate to an aqueous solution of
bromide ions in a test-tube. The student then adds a similar volume of dilute aqueous
ammonia to the same test-tube.
Describe what the student would see in the test-tube after the addition of aqueous
ammonia.
Answer: A cream precipitate would form.
2.
Chlorine reacts with aqueous sodium hydroxide to form bleach.
Write the equation and state the conditions for this reaction.
Include the conditions.
The student is provided with an aqueous solution of calcium bromide that is contaminated
with calcium iodide.
The student carries out a chemical test with silver ions but this time needs to add a second
reagent to show that iodide ions are present.
State the second reagent that the student would need to add.
Answer: concentrated (aqueous) NH3
4.
In drinking water, HClO kills bacteria.
Write an equation to show how HClO can form in drinking water
Answer: Cl2 + H2O HClO + HCl
5.
Some scientists believe that chlorine compounds should not be present in drinking
water.
Suggest one reason why scientists may be worried by the presence of these compounds.
Answer: Chlorine compounds are carcinogenic
Chlorine compounds are toxic/ poisonous
Content preview
The halogens
Physical properties:
Þ the halogens are diatomic
Element State Colour Colour of vapour
I 2
Fluorine Gas Pale yellow -
Chlorine Gas Green -
Bromine Liquid Brown Brown
Iodine Solid Grey Purple
Reactivity:
Þ The halogens react by gaining an electron to form 1– Melting
halide ions
Reactivit point
Þ Reactivity decreases down the group because: y
* Atomic radius increases down the group
* The number of electrons increases down
the group
* The number of shells increases down the
Þ This decreases
group the attraction of the nucleus towards electrons due
to electron shielding and the outer shell being further from the nucleus
Melting/Boiling points:
Þ Melting/boiling is caused by intermolecular forces being overcome
by thermal energy
Þ Melting/boiling points increase going down the group because:
* The number of electrons increases down the
group
* Thisthermal
Þ More makes energy
the induced
is dipole-dipole forces
needed to overcome these
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