Calculating Acidity

Self-ionization of Water Both an acid and a base. (amphoteric) Can either give or receive a proton. A pair of water molecules are in equilibrium with two ions A sample of pure water contains H2O, H3O+, and OH-

Self-ionization of Water In pure water, concentration of two ions is equal. [H3O+] = [OH−] = 1.00 × 10−7 M

[H3O+][OH−] = Kw. (1.00 × 10−7)(1.00 × 10−7) = Kw= 1.00 × 10−14 So [H3O+][OH−] = 1.00 × 10−14 Kw is always constant Anything that increases one of the ion concentrations decreases the other. If you know one of the ion concentrations, you can calculate the other.

Calculate the [H3O+] and [OH−] of a 3.00 × 10−5 M solution of HCl?

Calculate the [H3O+] and [OH−] of a 0.00350M H2SO4 solution.

A solution is made by dissolving 0. 100 mol of Mg(OH)2 in 1 A solution is made by dissolving 0.100 mol of Mg(OH)2 in 1.00 L of water. Find the [OH-] and [H3O+] of the solution.

The concentration of hydronium ions in a solution expresses its acidity. The concentration of hydroxide ions in a solution expresses its basicity.

When acidity and basicity are exactly balanced [H3O+] = [OH−] the solution is neutral. Pure water is neutral because it contains equal amounts of the two ions

pH measure of the acidity The letters p and H represent power of hydrogen. pH can be calculated pH = −log [H3O+]

As [H3O+] increases, the pH will decrease. A solution of pH 0 is very acidic. A solution of pH 7 is neutral. A solution of pH 14 is very basic (or alkaline).

Sig Figs When you take the log of a number with N significant figures, the result should have N decimal places. log 0.00724 = -2.140 When raising 10 to a power (taking an inverse log): If the power of 10 has N decimal places, the result should have N significant figures. 102.890 = 776

What is the pH of (a) a 0. 000 10 M solution of HNO3 (b) a 0 What is the pH of (a) a 0.000 10 M solution of HNO3 (b) a 0.0136 M solution of KOH?

What are the concentrations of the [H3O+] and [OH−] in a sample of rain that has a pH of 5.05?

pOH is the measure of the basicity of a substance pOH = -log[OH-] On the pOH scale Below 7 is basic 7 is neutral Above 7 is acidic

pH and pOH are flip sides of the same coin They are related in that pH + pOH = 14

Find the pH, pOH, [H3O+] and [OH−] of a 1L of a solution that contains 0.015mol Ca(OH)2.

Find the pH, [H3O+], and [OH−] of a solution with pOH=9.3.

Indicators, turn different colors in solutions of different pH. An indicator a compound that can reversibly change color depending on the pH of the solution or other chemical change.

A pH meter is an electronic instrument equipped with a probe that can be dipped into a solution. The probe has two electrodes, one of which is sensitive to the hydronium ion. An electrical voltage develops between the two electrodes, and the circuitry measures this voltage. The instrument converts the measurement into a pH reading, which is displayed on the meter’s screen.