Notes for Acid Base

8/4/2019 Notes for Acid Base

1/6

Acids

An acid is a chemical substance which ionises in water to produce hydrogen ions, H+ /

hydroxonium ions, H3O+.

H+(aq) + H2O(l) > H3O+(aq)

Example: HCl(g) + H2O(l) > H3O+

(aq) + Cl-

(aq)

Acid Acid name Ions

HCl Hydrochloric acid H+, Cl -

HNO3 Nitric acid H+, NO3

-

H2SO4 Sulphuric acid H+, SO4

2-

CH3COOH Ethanoic acid H+, CH3COO

-

Monoprotic acid = acid can produce only one hydrogen ion per molecule in water.

(Example: HCl)

Diprotic acid = acid can produce two hydrogen ions per molecule in water. (Example:

H2SO4) Triprotic acid = acid can produce three hydrogen ions per molecule in water. (Example:

H3PO4)

Bases / Alkalis

A base is a chemical substance which reacts with an acid to produce a salt and wateronly.

Base(s) + acid(aq) > salt + water (l).

Example: NaOH(s) + HCl(aq) > NaCl(aq) + H2O(l)

Base Formula Solubility in water Ions in theaqueoussolution

Copper(II) oxide CuO Insoluble base -

Lead(II) oxide PbO Insoluble base -

Magnesium oxide MgO Insoluble base -

Zinc hydroxide Zn(OH)2 Insoluble base -

Aluminium hydroxide Al(OH)3 Insoluble base -

Sodium oxide Na2O Soluble base (alkali) Na+, O2-

Calcium oxide CaO Soluble base (alkali) Ca2+, O2-

Sodium hydroxide NaOH Soluble base (alkali) Na+, OH-

Potassium hydroxide KOH Soluble base (alkali) K +, OH-

Barium hydroxide Ba(OH)2 Soluble base (alkali) Ba2+, OH-


2/6

The Uses of Acids in Our Daily Life

Benzoic acid Its salt are used to preserve food

Carbonic acid To make carbonated drinks

Ethanoic acid A main compound of vinegar

Hydrochloric

acid

To clean metals before electroplating /

household cleaning / leather processing /swimming pool maintenance

Nitric acid Production of fertilisers, explosives,

etching and dissolution of metals(purification and extraction of gold)

Sulphuric acid To make detergent, polymer and fertilisers.

Tartaric acid Manufacturing of soft drinks, provide

tartness to food, as an emetic (a substance

to induce vomiting)

The Uses of Bases in Our Daily Life

Ammonia Production of fertilisers (ammonium andnitrate salts), used in the manufacture of

nitric acid, neutralise the acid (in the

petroleum industry) and prevent prematurecoagulation in natural / synthetic latex.

Aluminium

hydroxide

Manufacture other aluminium compound

and to make gastric medicine (antacid)

Calciumhydroxide To make cement, limewater, neutralise theacidity of soil and application of sewagetreatment.

Sodium

hydroxide

Used in the manufacturing of soups,

detergents, and cleaners.

Magnesium

hydroxide

Suspension of magnesium hydroxide inwater are used as an antacid, used as an

antiperspirant armpit deodorant and as a

non-hazardous alkali to neutralise acidicwastewater.

Chemical Properties


3/6

.

.

.

.

.

..

.

.

.

.

.

.

.

.

.

..

.

.

.

.

.

.

.

.

.

.

Important Definition for

Acids

Monoprotic acid (monobasic acid) is an acid which produce one mole of H+ ion when one mole

of the acid ionise in water.

Monoprotic

acid

Monoprotic acid name

HCl Hydrochloric acid

HNO3 Nitric acidCH3COOH Ethanoic acid

.

Acid Alkali

In the presence of water, an acid

will ionise to form hydrogen ion,

H+.

In the presence of water, an alkali

will ionise to form hydroxide ion,

OH -.

Sour in taste Bitter in taste

pH values less than 7 pH values more than 7

Indicator: Blue litmus paper

(Red)

Indicator: Red litmus paper (Blue)

Indicator: Universal indicator(Orange and red)

Indicator: Universal indicator (Blue

and purple)

Indicator: Methyl orange (Red) Indicator: Methyl orange (Yellow)

React with bases to produce saltsand water.

2HCl(aq) + CuO(s) > CuCl2(aq)

+ H2O(l)

React with acids to produce salts

and water.

NaOH(aq) + HCl(aq) > NaCl(aq)

+ H2O(l)React with metals (reactive

metal, higher position than H+ in

the electrochemical series) toproduce salts and hydrogen gas.

2HCl(aq) + Zn(s) > ZnCl2(aq) +

H2(g)

React with an ammonium salt

(alkali is heated) to produce

ammonia gas.

Ba(OH)2(aq) + 2NH4Cl(s) >BaCl2(aq) + 2H2O(l) + 2NH3(g)

React with carbonates to produce

salts, carbon dioxide gas and

water.

H2SO4(aq) + ZnCO3(s) >

ZnSO4(aq) + H2O(l) + CO2(g)

React with aqueous salt solutions toproduce metal hydroxides (as

precipitate).

2NaOH(aq) + CuSO4(aq) >

Na2SO4(aq) + Cu(OH)2(s)


4/6

Polyprotic acids

Diprotic acid (dibasic acid) is an acid which produce two moles of H+ ios from one mole of the

acid in water.

Diprotic acid Diprotic acid name

H2SO4 Sulphuric acid

H2CO3 Carbonic acid

H2CrO4 Chromic acid

H2C2O4 Ethanedioic acid /

Oxalate acid

Triprotic acid (tribasic acid) is an acid which produce three moles of H+ ions from one mole of

the acid in water.

Triprotic acid Triprotic acid name

H3PO4 Phosphoric acid

C6H8O7 Citric acid

The pH scale and the Measurement of pH Value of a Solution

pH scale is a set of numbers used to represent the degree of acidity or alkalinity of a

solution. pH is a measurement of the concentration of hydrogen ions (H+) in the solution.

pH value greater than 7: alkaline solution pH value of exactly 7: neutral solution

pH value less than 7: acidic solution

In an acidic solution = higher in the concentration of the H+ ions, the lower the pH value.

In an alkaline solution = lower in the concentration of the H+ ions, the higher the pH

value.

pH solution can be measured by using universal indicator, pH paper and pH meter.


5/6

pH value Colour of Universal

Indicator

0, 1, 2 Red

3 Orange red

4 Orange

5 Orange yellow

6 Yellow

7 Green

8 Greenish-blue

9 Blue

10 Blue

11 Bluish-purple

12, 13, 14 Purple

Concentration of Acids and Alkalis

Quantity of solute can be measured in grams or moles: g dm-3 or mol dm-3.

Concentration (g dm-3) = mass of solute (g) / volume of solution (dm3)

Concentration (mol dm-3) = number of moles of solute (mol) / volume of solution (dm3)

Relationship between Number of Moles with Molarity and Volume of a Solution

Molarity (mol dm-3) = number of moles of solution (mol) / volume of solution (dm3)

M = molarity of solution (mol dm-3), V = Volume of solution (dm3), n = Number of moles

of solute (mol) M = n/V

Preparation of Standard Solutions

Standard solution = a solution in which its concentration is accurately known.

Standard solution is prepared by using volumetric flask with a fixed volume (100 cm3,

200 cm3, 250 cm3, 500 cm3 and 1000 cm3)

Preparation of a Solution by Dilution Method

Dilution = a process of diluting a concentrated solution by adding a solvent (water) toobtain a more diluted solution.

The concentration of the solution decreases after dilution.

The number of moles of solute in the solution remains unchanged after dilution.

(MaVa) / 1000 = (MbVb) / 1000 Ma = Initial molarity of solution, Mb = Final molarity of solution, Va = Initial volume of

solution and Vb = Final volume of solution


6/6

Relationship between pH Values and Molarities of Acids or Alkalis

pH values depends on degree of dissociation and molarity / concentration of hydrogen

ions, H+

/ hydroxide ions, OH-

in the solution. The higher the molarity of a strong acid, the lower is its pH value.

The higher the molarity of a strong alkali, the higher is its pH value.

The molarity of an acid can be changed when

(i) water is added,

(ii) an acid of different concentration is added and

(iii) an alkali is added.

Documents

Notes for Acid Base