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Acid
,→Key Stage 4
==Key Stage 4==
===Meaning===
An [[acid]] is a [[compound]] which is able to donate [[Hydrogen Ion(Chemistry)|H<sup>+</sup> ions]] when [[dissolve]]d in [[water]] to produce a [[solution]] with a [[pH]] less than [[Neutral (Chemistry)|7]].
===About Acids===
====Foundation====
: [[Acid]]s form from [[Ionic Compound|ionic compounds]] where there is an [[Ionic Bond|ionic bond]] between a [[Hydrogen Ion(Chemistry)|Hydrogen ion]] and another part of the [[molecule]].: When an [[acid]]ic [[compound]] [[dissolve]]s in [[water]] the [[Hydrogen Ion(Chemistry)|Hydrogen ion]] becomes dissociated from the [[molecule]] and is free to move separately in the [[solution]].: The [[Hydrogen Ion(Chemistry)|Hydrogen ion]]s in an [[acid]] will accept [[electron]]s from any [[metal]] which is higher on the [[Reactivity Series|reactivity series]] than [[Hydrogen]]. This is because those [[metal]]s can lose their [[electron]]s more easily than the [[Hydrogen]] [[atom]].: The [[acidity]] of an [[acid]] is measured on the [[pH]] scale. The more [[Hydrogen Ion(Chemistry)|Hydrogen ions]] in a [[solution]] the lower the [[pH]].
There are several common [[Chemical Reaction|reactions]] of [[acid]]s you should know:
*[[Acid + Metal → Metal Salt + Hydrogen]]
====Higher====
: The [[concentration]] of an [[acid]] is determined by how many [[gram]]s of [[acid]] are [[dissolve]] per [[litre]] ([[decimetre cubed]]) of [[water]]. A [[dilute]] [[acid]] has very little [[compound]] [[dissolve]]d per [[litre]] while a [[concentration|concentrated]] [[acid]] has a large [[mass]] of [[compound]] [[dissolve]]d per [[litre]].
: When a [[compound]] does [[dissolve]] in [[water]] to produce an [[acid]] not all of the [[Hydrogen Ion(Chemistry)|Hydrogen ion]]s will dissociate from the [[compound]]. The strength of an [[acid]], or its [[acidity]], is determined by how easily [[Hydrogen Ion(Chemistry)|Hydrogen ions]] are formed. The more easily [[Hydrogen Ion(Chemistry)|Hydrogen ions]] form, the stronger the [[acid]] (the higher the [[acidity]].: For a [[pH]] decrease of 1 there needs to be 10 times the number of dissociated [[Hydrogen Ion(Chemistry)|Hydrogen ions]] per [[litre]]. This will be affected by the [[concentration]] of [[acid]] and the strength of the [[acid]] ([[acidity]]).