Cations formed by hydrogen nuclide protium can be regarded as protons.But the cation formed by the other two nuclides, deuterium and tritium, can only be called hydrogen ion instead of proton.
Formation process
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Formation of hydrogen ions in solution
Usually formed by acid inwaterMedium ionization occurs.someAcid saltIt can also directly form hydrogen ions during ionization, such asSodium bisulfate；Water itself will ionize a very small amount of hydrogen ions andHydroxyl ion(Strictly speaking, the formula cannot be written as HtwoO=H++ OH-Because hydrogen ions are easily attracted by other water molecules, the strict formula should be 2HtwoO=HthreeO++ OH-, but can be written as H under certain circumstancestwoO=H++ OH-）。someStrong acid weak base saltAlthough hydrogen ions are not directly generated during ionization, some cations that can convert a small amount of hydroxyl ions in water into precipitation or gas will be ionized, thus increasing the number of hydrogen ions in water, such ascopper sulphate、ammonium sulphateEtc.
At room temperature,dilute solutionThe product of hydrogen ion concentration and hydroxyl ion concentration (i.eIonic product）Always 1.0 × 10-14。We use the negative of hydrogen ionlogarithmIndicate solutionPH, i.epH。
So pH of pure water=- lg10-7=7.0。There is no doubt that the hydrogen ion concentration of acid solution is always greater than 1.0 × 10-7mol/L，andAlkaline solutionThe hydrogen ion concentration of is always less than 1.0 × 10-7mol/L。Therefore, pH of acidic solution is less than 7, and pH of alkaline solution is more than 7,Neutral solutionpH=7。
PH test paper
It is worth noting that the pH value of the solution is not always between 0-14, and sometimes a value greater than 14 ornegative。And our extensivePH test paperGenerally, only solutions with pH between 0-14 can be tested, and only integer values can be taken.The pH meter can measure decimals.
1．Kw=c（H+）·c（OH-）, c (H) in pure water+）=c（OH-）, pure water always presentsElectroneutralityOf.
2. It cannot be considered that c (H+）Or c (OH-）Equal to 10-7mol/LOr pH=7 must beNeutral solutionThat is, pH=7 cannot be used to judge the acidity and alkalinity of all solutionsDividing line, compare c (H+）And c (OH-）The relative size of the two.The solution isAcid-base propertyThe essence of C (H+）≠c（OH-）。
3. c (H) produced by known water ionization+）Or c (OH-）It is not possible to finally determine theAcid-base property, because it may be an acid (or acid) solution or an alkali (or alkaline) solution.For example, c (H) ionized by water+）=1×10-13Mol/L solution, whose pH is equal to 1 or 13.
(1) It can be broken by adding acid and alkaliIonization of waterBalance, which makes the ionization balance of water move inversely, leading to c (H+）≠c（OH-）, water ionization is inhibited.C (H) expressed by pH of acid solution+）It is generated by the ionization of solute acid, through Kw=c (H+）·c（OH-）waterC (OH) of effluent ionization can be calculated-）water, and c (H+）water=c（OH-）water。C (H) expressed by pH of alkali solution+）Is c (H) ionized by water+）water, because the alkali itself cannot ionize H+.
(2) Temperature will affect the ionization equilibrium of water.Ionization of wateryesEndothermic process, temperature increases, promotes water ionization, Kw increases, pH decreases, but there is still c (H+）water=c（OH-）water。At room temperature, Kw=10-14；Kw=10 at 100 ℃-12。
(3) The salt that can hydrolyze can promote the ionization of water, thus breaking the ionization balance of water.Only one weak acid radicalanion(orweak alkalication）Hydrolysis, then c (H+）≠c（OH-）；If the added salt occursDouble hydrolysis, the concentration of the two ions may or may not be equal.Acidic by hydrolysisSalt solutionPH represents c (H) of water ionization+）water(same as alkaline solution), pOH (pOH=-lgc（OH-））Is the water ionized c (OH-）water(Same as acid solution).
5. For extremely dilute acid and alkali solutions,Ionization of waterCan not be ignored.For example: c (H+）=10-8Mol/Lhydrochloric acidIt is wrong to think that pH=8, because the pH of acid solution must be less than 7 at room temperature.At this time, when calculating the pH of the solution, the c (H+）waterAnd c (OH-）water。
