Acid and Bases

 

1. An acid is a substance that contains hydrogen ion , H⁺ , ad the only positive ions in aqueous solution
2. Abase is a substance that react with an acid to give only a salt and water
3. The presence of water is essential for the formation oh hydrogen ion. H⁺ and hydroxide ions, OH^-, in the aqueous solution

Strength of Acid and Alkalis

 

1. All aqueous acid has a sour taste. They show similar chemical properties.

a)     They have a pH value less than 7 and turn litmus papers from blue to red

b)     Most dilute acids react with metals (excepts copper, silver and gold) to form hydrogen has and salts

c)     They react with metallic carbonates to form carbon dioxide, water and salts

d)     They react with bases to form only salts and water in neutralisation

2. Chemical properties of alkalis include

a)     Have a bitter taste

b)     Impart a soapy feel to the skin

c)     Have a pH value greater than 7 and turn red litmus papers blue

d)     React with acids to give only salts and water in neutralization reaction

e)     React with ammonium salts when heated to produce ammonia gas.

3. The pH scale is a measure of how acidic or alkali an aqueous solution is
4. Strong acid contain acid molecule that fully ionize (dissociate) in aqueous solutions to produce a higher concentration of hydrogen ions.
5. Weak acid contain acid molecules that only partially ionize in aqueous solution to produce a lower concentration of hydrogen ions
6. A strong alkali is almost completely dissociated when dissolved in water to produce a higher concentration of hydroxide ions. This mean that strong alkalis consist almost completely of ions in the aqueous solution
7. A weak alkali is only partially dissociated in water to produce a lower concentration of hydroxide ions. This mean that weak alkalis consist mostly of molecules in aqueous solution
8. The pH value of a strong acid is lower than that of a weak acid of the same concentration
9. The pH value of strong alkali is higher than that of a weak alkali of the same concentration

Concentration of acid and alkalis

 

1. The concentration of a solution is the amount of a solute that dissolve in a unit volume of a solution
2. The concentration of a solution can be expressed in terms of
1. grams of solute per litre (dm³) of solution , g dm^-3

 

Concentration (g dm^-3) =       mass of solute (g)     

                                         Volume of solution (dm³)

 

2. Number of moles of solute per litre (dm3) of solution , mol dm-3

 

Concentration (mol dm^-3) =  number of moles of solute

                                               Volume of solution (dm³)

 

 

Neutralisation

 

1. The reaction between and acid and a based ( or alkali) to produce only water and a salt is called neutralisation
2. Acid- based titration is a quantitative experiment technique used to carry out completely neutralisation reaction between and acid and an alkali
3. the relationship between the acid and alkali in acid-based titration can be expressed using the following formula

 

 

M_aV_a         =     a

M_bV_b                b

M_a is molarity of acid

M_b is molarity of alkali

V_a is the volume of acid

V_b is the volume of alkali

A is the number of mole of acid shown in the chemical equation

B is the number of mole of alkali shown in the chemical equation.

 

 

EXERCISE

 

1.  
1. Name three acid, three bases and three salt and state its uses
2. You are provided with marble chips and glacial ethanoic acid. Describe an experiment to show that without water, an acid does not show acidic properties.
3. All variable involved
4. Procedures of experiment
5. Tabulation of result

 

2.  
1. describe how you can prepare 250 cm³ standard sodium solution of molarity 0.5 mole dm-3 (H,1; O,16; Na,23)
2. 25.0 cm³ if this standard NaOH solution is neutralized by 15.00 cm3 of sulphuric acid. Calculate the molarity of the acid
3. Explain why the pH of 0.1 M HCl solution is 1 whereas the pH of 0.1 M CH₃COOH solution is 4, although their concentrations are the same.