Chemistry: Mid-semester Break Work

ACID AND BASES

Acid

-chemical substances which IONISES IN WATERto produce hydrogen ion, H⁺ // hydroxonium ion, H₃O⁺

-examples of acid:

·         hydrochloric acid, HCl

·         sulphuric acid, H₂SO₄

·         nitric acid, HNO₃

-BASICITY OF AN ACIDis number of ionisable hydrogen atom per molecule of an acid molecule in an aqueous solution

o   monoprotic : one acid molecule ionises to one H⁺ ion

o   diprotic : one acid molecule ionises to two H⁺ ion

o   triprotic : one acid molecule ionises to three H⁺ ion

-examples:

MONOPROTIC	DIPROTIC	TRIPROTIC
Nitric acid, HNO3	Sulphuric acid, H2SO4	Phosphoric acid, H3PO4
Ethanoic acid, CH3COOH	Carbonic acid, H2CO3

Bases

-chemical substance which ionises in water to produce hydroxide ion, OH^-

-most bases are insoluble in water BUT bases that are soluble in water is called ALKALI

-example:

SOLUBLE BASE; ALKALI	INSOLUBLE BASE
Sodium oxide, Na2O	Copper(ll) oxide, CuO
Ammonia, NH3	Aluminium oxide, Al2O3
Barium hydroxide, Ba(OH)2	Lead(ll) hydroxide, Pb(OH)2

Chemical Properties Of Acid And Alkali

ACID		ALKALI
Reaction with metal	Acid + metal → salt + H2	Reaction with acid	Acid + alkali → H2O + salt
Reaction with metal carbonate	Acid + metal carbonate → salt + H2O + CO2	Reaction with ammonium salt	Alkali + ammonium salt→ salt + H2O + NH3
Reaction with alkali	Acid + alkali →H2O + salt	Reaction with metal ion	Alkali + metal ion → insoluble metal hydroxide

-Acid and Alkali only show their chemical properties when dissolved in water because it has free moving H⁺ ion (for acid) and OH^- ion (for alkali). They also conduct electricity for the same reason.

The pH Scale

-a scale of numbers to measure the degree of acidity and alkalinity of an aqueous solution based on the concentration of H⁺ ions or OH^- ions

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

pH < 7

·         acidic solution

·         lower pH, higher H⁺ concentration

pH = 7→ neutral

pH > 7

·         alkaline solution

·         higher pH, higher OH^- concentration

-How to measure pH value?

·         pH meter

·         acid-base indicator

Indicator	Colour
	Acid	Neutral	Alkali
Litmus solution	Red	Purple	Blue
Methyl orange	Red	Orange	Yellow
Phenolphthalein	Colourless	Colourless	Pink
Universal indicator	Red	Green	Purple

The Strength of Acid and Alkali

a)      Strong acid = acid that ionises completely in water to produce high concentration of H⁺ ion

b)      Weak acid = acid that ionises partially in water to produce low concentration of H⁺ ion

c)       Strong alkali = alkali that ionises completely in water to produce high concentration of OH^- ion

d)      Weak alkali = alkali that ionises partially in water to produce low concentration of OH^- ion

-Examples

Acid		Alkali
Strong	Weak	Strong	Weak
Hydrochloric acid	Carbonic acid	Sodium hydroxide	Ammonia solution
Sulphuric acid	Ethanoic acid	Potassium hydroxide

Concentration of Acid and Alkali

-Solution = Solute + Solvent

Concentration of solution(〖moldm〗^(-3) )/ molarity=(number of mole of solute (mol))/(volume of solution (〖dm〗^3))

Concentration of solution(〖gdm〗^(-3))= (number of solute in gram (g))/(volume of solution (〖dm〗^3))

Preparation of Standard Solution

-Standard solution is a solution in which its concentration is accurately known

-Steps to prepare standard solution

v  Calculate the mass of solute needed to give the required volume and molarity

v  The solute is weighed

v  The solute is completely dissolved in distilled water and then transferred to a volumetric flask partially filled with distilled water

v  Distilled water is added until the calibration mark of the volumetric flask and the flask is inverted to make sure thorough mixing.

Preparation of Solution by Dilution

-Adding water to the standard solution lowered the concentration of the solution. The number of solute does not change because no solute is added.

Number of mol of solute before dilution = Number of mol of solute after dilution

(M_1 V_1)/1000= (M_2 V_2)/1000

∴M_1 V_1= M_2 V_2

M1 = Initial concentration of the solute

V1 = Initial volume of solution in cm3

M2 = Final concentration of the solute

V2 = Final volume of solution in cm3

*note that this note is for the topics that going to be tested in UPSS 2

*i'm sorry about the equations, my mistake.

*goodluck in chemistry