pH ScaleIn this presentation you will:explore how to measure the strength of acids and basesNext >

Next >IntroductionAcids and bases can be measured with the pH scale which specifies the concentration of hydrogen ions, H+, in a solution.To show the concentration, the ion is enclosed in square brackets, [H+].

pH ScalePure (distilled) water has a pH of 7. The strongest acids are around pH 0, and the stronger bases around pH 14. Next >The pH scale is shown for some common substances.

pH ScaleAs the pH scale is logarithmic, change in the acidity or basicity of a solution of one whole pH unit actually represents a change of ten times the concentration of hydrogen ions in the solution.Next >

The pH value is the negative logarithm of the H+ ion concentration:pH ScalepH = - log10 [H+]Next >The pH of an acidic or basic solution can be calculated from the concentration of H+ ions in the solution.

pH ScaleNext >The concentration of hydrogen ions in most aqueous solutions is between 110-14 M and 1 M.

pH ScaleNext >Concentration M in moles per liter is sometimes expressed as mol/dm3. These are equivalent terms.From pH = - log10 (10-14) = 14 to pH = - log10 (1) = 0Therefore, the range of pH values for these solutions is between 14 and 0:

pH Calculations Strong AcidsA strong acid is fully dissociated into H+ ions and its associated base ions (known as its conjugate base) in aqueous solution.Next >A strong acid is one that fully ionizes, or dissociates into its ions, in an aqueous solution.

pH Calculations Strong AcidsNext >This makes pH calculations of strong acids, of known concentration, simple to work out.The molar concentration of H+ will be equal to the concentration of the acid.

pH Calculations Strong AcidsIn a 0.25 M solution of HCl, the concentration of H+ ions is also 0.25 M.HCl(aq) H+(aq) + Cl-(aq)pH = 0.6pH = - log10 [0.25]pH = - log10 [H+]Next >[HCl] = [H+] = [Cl-] = 0.25 mol/LHence:

pH Calculations Strong BasesThe ionic product of water (Kw) is used to calculate the pH of bases. H2O(l) H+(aq) + OH-(aq)However, in alkaline solutions, the concentration of H+ ions is extremely low. Next >Like strong acids, strong bases are fully dissociated into ions. Kw = [H+] [OH-] = 1 1014 mol/L

pH Calculations Strong BasesH2O(l) H+(aq) + OH-(aq)Next >To calculate the concentration of H+ ions in a basic solution, we have to rearrange this equation.Water naturally dissociates into H+ and OH ions with equal concentrations of 1107 mol/L at 298 K. Kw = [H+] [OH-] = 1 1014 mol/L [H+] = Kw / [OH-]

Consider a solution of NaOH of 0.25 M concentration at 298 K:[H+] = 1 1014 / 0.25 = 4 10-14 mol/LTo calculate the ionic product of water: [NaOH] = [Na+] = [OH-] = 0.25Next >pH Calculations Strong Bases pH = - log10 (4 10-14 ) = 13.4Kw = [H+] [OH-] = 1 1014 mol/LpH = - log10 [H+]Therefore, the pH of NaOH is:

It is also possible to use the concentration of the hydroxide ion (OH-) to measure the strength of an acid or base, as pOH.Next >Relationship between pH and pOHKw = [H+] [OH-] = 1 1014 mol/LpH = - log10 [H+]

For a given concentration of hydrogen, say [H+] = 1 107 mol/LIn this case, pH = 7 and pOH = 7Next >Relationship between pH and pOHthen, [OH-] = Kw / [H+] = 1 1014 / 1 107 = 1 107 mol/LpOH = - log10 [OH-]Since, pH = - log10 [H+], thenpOH = - log10 [OH-] = - log10 (1 107 ) = 7Example

Next >Relationship between pH and pOHIn all cases, the sum of pOH and pH will equal 14 because of the relationship:Given either pOH or pH, then for any acid or base the other can be calculated.Kw = [H+] [OH-] = 1 1014 mol/LpOH + pH = 14

Measuring pHIt is often necessary to know the pH of a solution, in order to identify it as acidic or basic. Next >Additionally, pH changes during a reaction must often be continuously monitored, for example in a titration experiment.

Measuring pHThe most common experimental techniques used for finding pH are:Indicators, or chemical substances that react to different pH levels by changing color. Next >

Measuring pHNext >The most common experimental techniques used for finding pH are:pH meter, an instrument which measures the pH directly.Universal pH indicator paper, which changes color with pH. A chart is used to identify the pH range shown by each color.

The concentration of hydrogen ions in a solution with a pH of 1 is...?Question 1A) twice the concentration of a solution with a pH 2.B) half the concentration of a solution with a pH 2.C) ten times the concentration of a solution with a pH 2.D) a tenth of the concentration of a solution with a pH 2.Next >

Next >Question 1The concentration of hydrogen ions in a solution with a pH of 1 is...?A) twice the concentration of a solution with a pH 2.B) half the concentration of a solution with a pH 2.C) ten times the concentration of a solution with a pH 2.D) a tenth of the concentration of a solution with a pH 2.

What is the hydroxide ion concentration for a 1 10-4 M HCl solution?Question 2A) 1 10-4 MB) 1 10-6 MC) 1 10-8 MD) 1 10-10 MNext >

Next >Question 2What is the hydroxide ion concentration for a 1 10-4 M HCl solution?A) 1 10-4 MB) 1 10-6 MC) 1 10-8 MD) 1 10-10 M

In this presentation you have seen:Summaryan explanation of the pH scaleEnd >pH calculation of an acid and a base the relationship between pH and pOH

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