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Difference between revisions of "Alkali"

(About Alkalis)
 
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: [[Alkali]]s can be used to [[Neutralisation|neutralise]] [[acid]]s.
 
: [[Alkali]]s can be used to [[Neutralisation|neutralise]] [[acid]]s.
 
: [[Alkali]]s can be [[concentrated]] or [[dilute]].
 
: [[Alkali]]s can be [[concentrated]] or [[dilute]].
: [[Alkali]]s can be weak or strong which depends on the type of [[alkali]] and the [[concentration]].
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: [[Alkali]]s can be weak or strong which depends on the type of [[alkali]].
 
: [[Alkali]]s turn [[Litmus]] paper blue.
 
: [[Alkali]]s turn [[Litmus]] paper blue.
 
: [[Alkali]]s turn [[Universal Indicator]] blue, indigo and purple depending on the strength of the [[alkali]].
 
: [[Alkali]]s turn [[Universal Indicator]] blue, indigo and purple depending on the strength of the [[alkali]].

Latest revision as of 22:49, 26 February 2022

Key Stage 3

Meaning

An alkali is a Metal Hydroxide solution that has a pH more than 7.

Noun: Alkali
Adjective: Alkaline

About Alkalis

Alkalis can be an Irritant, Harmful or Corrosive and should be handled with care.
Alkalis can be used to neutralise acids.
Alkalis can be concentrated or dilute.
Alkalis can be weak or strong which depends on the type of alkali.
Alkalis turn Litmus paper blue.
Alkalis turn Universal Indicator blue, indigo and purple depending on the strength of the alkali.

Some common Alkalis you should know:

Key Stage 4

Meaning

An alkali is basic compound which dissolves in water to form OH- ions making a solution with pH greater than 7.

About Alkalis

Alkalis are bases in solution which form Hydroxide ions.
When a baseic compound dissolves in water a Hydroxide ion becomes dissociated from either the basic compound or from a water molecule. That Hydroxide ion is free to move separately in the solution.
The Hydroxide ions in an alkali will donate electrons to Hydrogen ions to form water. This is a neutralisation reaction.
The strength of an alkali is measured on the pH scale. The more Hydroxide ions in a solution the lower the pH.

Examples

Metal Hydroxides form Hydroxide ions in water.

NaOH(aq) → Na+(aq)+OH-(aq)
KOH(aq) → K+(aq)+OH-(aq)
Mg(OH)2(aq) → Mg+2(aq)+2OH-(aq)
Ca(OH)2(aq) → Ca+2(aq)+2OH-(aq)
Al(OH)3(aq) → Al+3(aq)+3OH-(aq)

Metal Oxides react with water to produce Metal Hydroxides which also form Hydroxide ions.

Na2O(s) + H2O(l) → 2Na+(aq)+2OH-(aq)
K2O(s) + H2O(l) → 2K+(aq)+2OH-(aq)
MgO(s) + 2H2O(l) → Mg+2(aq)+2OH-(aq)
CaO(s) + 2H2O(l) → Ca+2(aq)+2OH-(aq)
Al2O3(s) + 3H2O(l) → 2Al+3(aq)+6OH-(aq)

Ammonia also reacts with water to produce Hydroxide ions:

NH3O(aq) + H2O(l) ⇌ NH4+(aq)+OH-(aq)

References

AQA

Alkali, pages 142-3, 148, 150, GCSE Chemistry; Student Book, Collins, AQA
Alkalis, page 128, GCSE Combined Science; The Revision Guide, CGP, AQA
Alkalis, pages 107, 112, 280, GCSE Chemistry, Hodder, AQA
Alkalis, pages 124-126, 130, GCSE Combined Science Trilogy; Chemistry, CGP, AQA
Alkalis, pages 146-151, 155, GCSE Chemistry, CGP, AQA
Alkalis, pages 209, 247, GCSE Combined Science Trilogy 1, Hodder, AQA
Alkalis, pages 51, 52, GCSE Chemistry; The Revision Guide, CGP, AQA
Alkalis, pages 74-77, 92, 94, 96-97, 163, GCSE Chemistry; Third Edition, Oxford University Press, AQA
Alkalis; reaction with acids, pages 249, 252-3, GCSE Combined Science Trilogy 1, Hodder, AQA

Edexcel

Alkalis, page 118, GCSE Chemistry, CGP, Edexcel
Alkalis, page 43, GCSE Chemistry; The Revision Guide, CGP, Edexcel
Alkalis, pages 105, 109, GCSE Combined Science; The Revision Guide, CGP, Edexcel
Alkalis, pages 196-197, 204-205, 208-209, GCSE Combined Science, Pearson Edexcel
Alkalis, pages 52-53, 60-61, 64-65, GCSE Chemistry, Pearson, Edexcel
Alkalis; reactions of, pages 185, 186, GCSE Chemistry, CGP, Edexcel
Alkalis; reactions of, pages 47, 65, GCSE Chemistry; The Revision Guide, CGP, Edexcel

OCR

Alkalis, pages 112, 114, Gateway GCSE Combined Science; The Revision Guide, CGP, OCR
Alkalis, pages 112-115, Gateway GCSE Chemistry, Oxford, OCR
Alkalis, pages 43, 45, 64, GCSE Chemistry; The Revision Guide, CGP, OCR Gateway