10 Class- Acids, Bases and Salts

Acids Bases and Salts

·       Natural indicator of acids and bases – Litmus, Turmeric

·       Synthetic indicator of acids and bases – Methyl Orange, Phenolphthalein

·       Olfactory indicators of acids and bases - Odor of these substance changes in acids and bases.

pH scale for Acid Neutral and Alkaline (or Base) & Acid Base strength indication by H and OH ion concentration

What is Acid?

Acids are the chemicals which can donate a proton or accept an electron pair in chemical reactions having pH less than 7 and changes color of blue Litmus to red.

Example- HCl, H₂SO₄

What is Base?

Bases are the chemicals which can accept a proton or donate an electron pair in chemical reactions having pH more than 7 and changes color of red Litmus to blue.

Bases which dissolve in water are called as Alkali

Example- NaOH

What is Salt?

Salt is a mineral or any neutral compound containing cations (+ve ions) attached with anions (-ve ions). 

Example- NaCl

Acids and Bases Reaction with Metals:-

                   Metal react with acid to form salt.

Acid + Metal ------> Salt + Hydrogen Gas

Similarly,

Metal react with base to form salt.

Base + Metal -------> Salt + Hydrogen Gas

Reaction of Metal Carbonates and Metal Hydrogen-Carbonates with Acids:-

Metal carbonates and metal hydrogen carbonates react with acids to form salt, water and carbon dioxide.

Metal Carbonate + Acid ----> Salt + Water + Carbon Dioxide

Example- Na₂CO₃ + 2HCl ---> 2NaCl + H₂O + CO₂

Similarly,

Metal Hydrogen Carbonate + Acid --> Salt + Water + Carbon Dioxide

Example- NaHCO₃ + HCl ---> NaCl + H₂O + CO₂

Reaction of Acids with Bases:-

Reaction of acids with bases to form salt and water is called neutralization reaction.

Acid + Base ----> Salt + Water

Reaction of Acids with Metallic Oxides:-

Acids react with Metallic Oxides to form salt and water.

Acid + Metallic Oxide ----> Salt + Water

Reaction of Bases with Non-Metallic Oxides:-

Non-Metallic Oxides are acidic in nature so these react with bases to form salt and water.

Base + Non-Metallic Oxide ----> Salt + Water

Acids or Bases in Water:-

When acids dissolve in water they produce Hydrogen Ion H⁺(Aq) or Hydronium Ion (H₃O⁺)

HCl + H₂O ----> H₃O⁺ + Cl^-

H⁺ + H₂O ---> H₃O⁺

When bases dissolve in water they produce Hydroxide Ions (OH^-)

NaOH + H₂O -------> Na⁺(Aq) + OH^-(Aq)

Reactions of Acids or Bases with Water are highly exothermic. Process of mixing Acid or Base with water decrease concentration of ions per unit volume, this process is known as dilution. 

Strength of Acids or Bases:-

Strength of acids depends on number of hydrogen ions (H⁺) produced and strength of bases depends on number of hydroxide ions (OH^-) produced. A universal indicator (present on pH paper) is used to find strength of acids or bases.

pH Scale:-

It is a scale to measure hydrogen ion concentration in solution.

pH also known by seeing the color change in litmus paper.

Meaning of ‘p’ in ‘pH’ is “potenz”, which is a German word whose meaning is “power”.

pH scale measure pH from 0 (very acidic) to 14 (very alkaline).

pH of Neutral Solution is 7

pH of Acidic Solution is less than 7

pH of Basic Solution is more than 7

How to Measure PH of Acids and Bases ?

You can measure pH of acids and bases with the help of litmus paper, pH paper and pH meter. To know pH of any substance watch below pH experiment conducted by the Chemistry Notes Info. 

What is acid rain?

If pH of rain water is below 5.6 on pH scale than, that rain is called as acid rain.

Some Naturally Occurring Acids:-

Natural Source	Acid
Vinegar	Acetic Acid
Orange	Citric Acid
Tamarind	Tartaric Acid
Tomato	Oxalic Acid
Sour Milk (Curd)	Lactic Acid
Lemon	Citric Acid
Ant Sting	Methanoic Acid
Nettle Sting	Methanoic Acid

Common Salt:-

Common salt is very important raw material for production of other daily use material.

Sodium Hydroxide:-

Sodium Hydroxide is obtained by passing electricity through aqueous solution of sodium chloride (brine). Process is known as Chlor-Alkanization.   

2NaCl (aq) + 2H₂O (l) ----> 2NaOH (aq) + Cl₂ (g) + H₂ (g)

Bleaching Powder (CaOCl₂):-

Bleaching Powder is obtained by reaction between chlorine (Cl₂) and dry slaked lime [Ca(OH)₂].

Ca(OH)₂ + Cl₂ -----> CaOCl₂ + H₂O

Use of Bleaching Powder:-

·       For bleaching wood pulp in paper industry.

·       For bleaching washed clothes in laundry.

·       For bleaching cotton and linen in textile industry.

·       Used as oxidizing agent in chemical industry.

·       Used as disinfectant for drinking water to kill germs.

Baking Soda:-

Chemical name of baking soda is sodium hydrogen carbonate (NaHCO₃). It is obtained by reaction between Sodium Chloride (NaCl), Water (H₂O), Carbon Dioxide (CO₂) and Ammonia (NH₃).

NaCl + H₂O + CO₂ + NH₃ ----> NH₄Cl (Ammonium Chloride) + NaHCO₃ (Sodium Hydrogen Carbonate)

Uses of Sodium Hydrogen Carbonate:-

·       To produce baking powder {mixture of baking soda + mild edible acid (like tartaric acid)}

·       Used to produce antacids (neutralize access acid in stomach to provide relief from acidity)

·       Used in soda acid fire extinguishers

Washing Soda:-

Washing soda is obtained by heating baking salt (Sodium Hydrogen Carbonate) and recrystallization of Sodium Carbonate produced above.

2NaHCO₃ (Sodium Hydrogen Carbonate) + Heat --------> Na₂CO₃ (Sodium Carbonate) + H₂O + CO₂

Na₂CO₃ + 10H₂O --------> Na₂CO₃.10H₂O

Uses of Washing Soda:-

·       Used in glass, soap and paper industries

·       Used in preparation of sodium compounds like borax

·       Used as cleaning agent

·       Used for removal of permanent hardness of water

Crystal of Salt:-

Presence of fixed no. of water molecules in one formula unit of salt is called as water of crystallization.

·       Copper sulphate crystals with water molecule (CuSO₄.5H₂O) are blue in color, while

·        Copper sulphate crystals without water molecule (CuSO₄) are white in color.

Plaster of Paris:-

Plaster of Paris is obtained by heating gypsum (CaSO₄.2H₂O) at 373K.

CaSO₄.2H₂O (Gypsum) + Heat ----> CaSO₄.1/2H₂O (Plaster of Paris) + 3/2H₂O

Uses of Plaster of Paris:-

·       Used by orthopedic doctors for supporting fractured bones.

10 Class- Periodic Classification of Elements

Periodic Classification of Elements

In year of 1800 about 30 elements were known but at present we know about 114 elements. All these elements have different properties. So to study about these elements easily, scientists start searching some patterns in the properties to arrange these elements.

Early Attempts in the Classification of Elements

                                                                   This is practice to arrange elements in order out of chaos, means arranging elements in group of metals and non-metals. Chaos means complete disorder or confusing. Furthermore attempts were made to achieve best classification of the elements.

Dobereiner’s Triads

                             A German chemist, Johann Wolfgang Dobereiner in 1817 tried to arrange elements in the group of 3-elements in each group with similar properties and he called these groups as ‘Triads’. Dobereiner shows that when we take any triad and arrange its elements in the order of increasing atomic masses then the atomic mass of the middle element in the triad is roughly equal to the average of the 1^st and 3^rd element of the triad.

Dobereiner Triads

Li Na K

Ca Sr Ba

Cl Br I

In first triad Li, Na, K atomic mass of   Na (23) = [ Li(7) + K(39)]/2

Newlands Law of Octaves

                                      An English scientist, John Newlands in 1866 arranges known elements in order of their increasing atomic masses. At that time he started with Hydrogen as 1^st element with lowest atomic mass and ended at Thorium as 56^th element.  John Newlands observe that the property of every eighth element  is similar to that of first element and compare this to octaves of music so he called it ‘Law of Octaves’ and this is known as ‘Newlands Law of Octaves’.

Newlands Octaves

H	Li	Be	B	C	N	O
F	Na	Mg	Al	Si	P	S
Cl	K	Ca	Cr	Ti	Mn	Fe
Co and Ni	Cu	Zn	Y	In	As	Se
Br	Rb	Sr	Ce and La	Zr	-	-

1.     Newlands law of octaves is applicable only up to Calcium and after Calcium it is not applicable because after Calcium every eighth element is do not similar to that of first element. 
2.     Newlands assumed only 56 elements exists in nature but later several elements discovered whose properties are very different to get fit in Newlands law of octaves. 
3.     With the discovery of new elements, Newlands try to fit these elements in octaves so he put two elements in same slot and Newland also put elements with different properties in same slot for example Co and Ni placed in F, Cl column.

Mendeleev’s Periodic Table

                                      A Russian chemist, Dmitri Ivonovich Mendeleev in 1872 published his ‘Mendeleev Periodic Table’ in a German journal.  He arranges elements in the form of table on the basis of fundamental property of elements i.e. atomic mass and also on the basis of similarity of chemical properties of elements, means elements with similar chemical properties are placed together in table.

Mendeleev Periodic Law

                             According to this law “the properties of elements are the periodic function of their atomic masses”.

In Mendeleev periodic table horizontal rows are called as ‘Periods’ and vertical columns are called as ‘Groups’.

Mendeléev’s Periodic Table

Achievements of Mendeléev’s Periodic Table

                                                          Mendeléev’s Periodic Table contains some gaps but Mendeléev predicted that these gaps are filled by elements discovered in future. And named these undiscovered elements by placing eka (one) as a prefix to the name of preceding element of the same group. For example Gallium discovered later but Mandeleev predict it as Eka-Aluminium.

Properties of Eka-Aluminium and Gallium

Property	Eka-Aluminium	Gallium
Atomic Mass	65	69.7
Formula of Oxide	E2O3	Ga2O3
Formula of Chloride	ECl3	GaCl3

This prediction of Mandeleev proves correctness and usefulness of Mendeléev’s Periodic Table. Another achievement of Mandeleev is that many scientists now recognize him as originator of the concept on which periodic table is based and also when inert gases (means Nobel gases like He, Ne, Ar) are discovered, they are placed in separate column without disturbing existing order of elements.

Limitation of Mandeleev Classification

                                                These given below are the limitation of Mandeleev Classification. 
1. Position of Hydrogen- No fixed position given to Hydrogen as it behaves like both alkali metals and halogens. Like alkali, Hydrogen react with halogen oxygen and sulphur and also like halogen, Hydrogen exist in diatomic form and react with metals and non-metals. 
2. Isotopes- Isotopes have similar chemical properties but different atomic masses, so Isotopes are challenge to Mandeleev Periodic Law. 
3. Prediction of New Elements- Atomic masses of elements do not increase in regular manner so we cannot predict how many elements can be discovered between two elements.

Modern Periodic Table

                             Henry Moseley in 1913, after performing many experiments proves that atomic number is more fundamental property than atomic mass of an element. So he prepare periodic table on the basis of atomic number means elements are arranged in the order of increasing atomic number in Modern Periodic Table.

Modern Periodic Law

                             According to this law “the properties of elements are the periodic function of their atomic number”.

In Modern Periodic Table limitation of Mandeleev Classification are removed. 

Modern Periodic Table

Position of Elements in Modern Periodic Table

                                                          Modern Periodic Table contains 18 vertical columns (means 18 Groups) and 7 horizontal rows (means 7 Periods).

In Group- Elements in a group have same number of valence electrons means identical outershell electronic configuration, but as we move downside in a group number of shells increases.

In Period- Elements in a period have same number of shells. Also as we move from left to right in a period, atomic number increases by one unit so number of valence shell electrons also increases by one unit.

Trends in the Modern Periodic Table

Valency

          Number of valence electrons in outer most shell of any atom is called valency of that atom. As we move from left to right in a period, atomic number increases by one unit so valence electrons also increases by one unit but in a group it remains constant.

Atomic Size

                   Atomic size is determined by atomic radius.

In a Period- Atomic radius decreases as we move from left to right in a period, because as we move from left to right in a period Nuclear Charge (+ve) increases which pulls electrons (-ve) towards nucleus result in decreasing atomic size or decrease atomic radius.

In a Group- Atomic radius increases as we move from top to bottom in a group, because new shells are added which increases distance between nucleus and outermost electrons.

Metallic and Non-metallic Properties

                                                Elements towards left hand side in periodic table are metals while elements towards right hand side in periodic table are non-metals. Elements which separate metals and non-metals have the properties of the both metals and non-metals are known as Metalloids or Semi-Metals.

Example of Metals- Na, Mg, Al, Fe

Example of Non-metals- S, Cl, F, Br

Examples of Metalloids or Semi-Metals- B, Si, Ge, As, Sb, Te, Po

In a Period- Metallic character decreases and Non-metallic character increases as we move from left to right in a period because tendency to lose valence electrons  decreases due to increasing nuclear charge as we move from left to right in a period.

In a Group- Metallic character increases and Non-metallic character decreases as we move from top to bottom in a group because tendency to lose valence electrons increases due to increasing valence shells (i.e. increasing distance between nucleus and outermost electron) on moving from top to bottom in a group.

Metals are electropositive as they forms bonds by loosing electrons while Nonmetals are electronegative as they forms bonds by gaining electrons.

In general cases, oxides of metals are basic in nature while oxides of non-metals are acidic in nature.