शनिवार, 10 सितंबर 2016

acid base salt

1. Acids: Acids are sour in taste, turn blue litmus red and give H3O+ ion (hydronium ions in solution. e.g. HCl, H2SO4, HNO3 etc
2. Bases: Bases are bitter in taste, have soapy touch, turns red litmus blue and give hydroxide ions (OH-) in solution. Example – NaOH, KOH etc
3. Salts: - A salt is a compound which is formed by neutralization reaction between an acid and base. For example, sodium chloride is formed by reaction between hydrochloric acid and sodium hydroxide.
Acid + base à Salt + water
HCl+NaOHàNaCl+H2O
4. Indicators - Indicators are substances which indicate the acidic or basic nature of the solution by their colour change. The colour of some acid-base indicators in acidic and basic medium are given below
INDICATORS
COLOUR IN ACIDIC MEDIUM
COLOUR IN BASIC MEDIUM
1. Litmus Solution
Red
Blue
2. Methyl Orange
Pink
Orange
3. Phenolphthalein
Colourless
Pink
4. Methyl Red
Yellow
Red

5 Chemical properties of acids
(i) Acids react with active metals to give hydrogen gas.

Zn + H2SO4à ZnSO4 + H2
(ii) Acids react with metal carbonate and metals hydrogen carbonate to give carbon dioxide.

NaHCO3+HCl à NaCl + H2O+CO2
(iii) Acids react with bases to give salt and water. This reaction is called neutralization reaction.

NaOH +HCl à NaCl + H2O+CO2
(iv) Acids react with metals oxides to give salt and water.

CuO + H2SO4 à CuSO4 + H2O
6 Chemical properties of Bases-
1. Reaction with Metals – Certain metals such as Zinc, Aluminum, Tin

react with Alkali solutions on heating and hydrogen gas is evolved
2NaOH + Zn → Na2ZnO2 + H2
2. Reaction with acids – Bases react with acids to form salt and water.

KOH + HCl → KCl + H2O
3. Reaction with Non – metallic oxides –
Non - metallic oxides are
generally acidic in nature. They react with bases to form salt and water.
2NaOH + CO2 → Na2CO3 + H2O
7. Strong and Weak Acids
An acid which completely dissociates into ions in aqueous solution is called strong acid such as HCl, H2SO4, and HNO3 etc. Weak acids are those which are weakly dissociated in its aqueous solution such as CH3COOH, H2CO3, and HCN etc. ]

8. Strong and Weak Bases
A base such as NaOH or KOH which is completely dissociated in aqueous solution is called a strong base. On the other hand a base which is weakly dissociated such as NH4 OH in its aqueous solution is called a weak base.

9. pH Scale

The concentration of hydrogen ions in solution is expressed in terms of pH. The pH of a solution is defined as the negative logarithm of hydrogen ion concentration in moles per litre.
pH =-log [H+]
pH =-log [H3O+]
where [H+] or [H3O+] represents concentrations of hydrogen ions in solution.
For water or neutral solutions, pH =7
For acidic solutions, pH< 7
 For basic solutions, pH > 7

10. pH of Salts
(a) pH of salts of strong acid – strong base such as NaCl=7

(b) pH of salts of strong acid – weak base such as CuSO4 is <7
(c) pH of salts of weak acid – and strong base such as CH3COONa >7

11. Some Important Chemical Compounds

(a) Common Salt (NaCl)

Sodium chloride is known as common salt .Its main source is sea water. It also exists in the form of rocks and sodium chloride obtained from rocks is called rock salt. Common salt is an important component of our food. It is also used for preparing sodium hydroxide, baking soda, washing soda etc.

(b) Sodium Hydroxide or Caustic Soda (NaOH)

Sodium hydroxide is prepared by passing electricity through an aqueous solution of sodium chloride (also known as brine).
2NaCl (aq) + 2H2O (l) 2NaOH (aq) + Cl2 (g) + H2 (g)
This process is known as chlor -alkali process due to the formation of chlorine and sodium hydroxide (an alkali) as the products.
Properties –
1. It is a white translucent solid.
2. It is readily soluble in water to give a strongly alkaline solution.
3. Crystals of sodium hydroxide are deliquescent.

(c) Bleaching Powder (CaOCl2)
Its chemical name is calcium oxychloride .It is prepared by passing chlorine gas through dry slaked lime.
Ca (OH) 2 + Cl2 CaOCl2 + H2O Slaked lime Bleaching powder
Uses-
1. For bleaching cotton and linen in textile industry.
2. For bleaching wood pulp in paper industry.
3. For disinfecting drinking water.
(d) Baking soda (NaHCO3)
Its chemical name is sodium hydrogen carbonate .It is prepared by passing CO2 gas through brine solution saturated with ammonia.
NaCl + H2O + CO2 + NH3 --------------------à    NH4Cl              +             NaHCO3
                                                                                     Ammonium chloride                                Sodium Hydrogen carbonate
The precipitated sodium hydrogen carbonate is filtered off.
 Properties
1. It is a white crystalline solid, sparingly soluble in water at room temperature.
2. Its aqueous solution is weakly alkaline due to hydrolysis.
3. On heating, it decomposes to give sodium carbonate and carbon dioxide.
2NaHCO3 Na2 CO3 + H2O + CO2 4.
It reacts with acids to give CO2 gas.
NaHCO3 + HCl NaCl + H2O + CO2
Uses-
1. It is used as a component of baking powder. In addition to sodium hydrogen carbonate baking soda contains tartaric acid.
2. It is used in soda- acid fire extinguisher.
3. It acts as mild antiseptic and antacid.
(e) Washing soda (Na2 CO3 .10 H2O)
Its chemical name is sodium carbonate decahydrate. It is obtained by heating baking soda in turn is obtained by passing CO2 gas through sodium chloride solution saturated with ammonia .
NaCl + H2O + CO2 + NH3 ------à       NH4Cl + NaHCO3
2 NaHCO3 ----------D----->      Na2 CO3             +       H2O + CO2
Sodium hydrogen carbonate            Sodium Carbonate
Recrystallisation of sodium carbonates gives washing soda.
Na2 CO3 + 10 H2O Na2 CO3 .10 H2O
Uses-
1. It is used in glass, soap and paper industries. 2. It is used for removing permanent hardness of water. 3. It can be used as a cleaning agent for domestic purposes.
(f)Plaster of Paris (CaSO4 ..1/2 H2O)
Its chemical name is calcium sulphate hemihydrate. It is obtained by heating Gypsum upto 373 K.
CaSO4 .2H2O ---D----à   CaSO4 ..1/2 H2O             + 11/2 H2O
     Gypsum                                                    Plaster of Paris
On treatment with water it is again converted into gypsum and sets as a hard mass.
 CaSO4 ..1/2 H2O  + 11/2 H2O -------à     CaSO4 .2H2O
Plaster of Paris                                                                                     Gypsum
Uses
1. It is used by Doctors for setting fractured bones.
2. It is used for making statues, models and other decorative materials.
 

















शनिवार, 30 जुलाई 2016

SOLUTION:class 12 chemistry



 
               assignment
                     SOLUTION
Question1 - Calculate the mass percentage of benzene (C6 H 6) and carbon tetrachloride (CCl 4) if 22 g of benzene is dissolved in 122 g of carbon tetrachloride.

Question 2 - Calculate the mole fraction of benzene in solution containing 30% by mass in carbon tetrachloride.

Question3 - Calculate the molarity of each of the following solutions:

(a) 30 g of Co(NO 3) 2. 6H2 O in 4.3 L of solution

(b) 30 mL of 0.5 M H 2SO4 diluted to 500 mL.

Question 4 - Calculate the mass of urea (NH2 CONH 2) required in making 2.5 kg of 0.25 molal aqueous solution.

Question5 - Calculate

(a) molality

(b) molarity and

(c) mole fraction of KI if the density of 20% (mass/mass) aqueous KI is 1.202 g mL – 1.

Question 6 - H 2S, a toxic gas with rotten egg like smell, is used for the qualitative analysis. If the solubility of H2 S in water at STP is 0.195 m, calculate Henry’s law constant.

Question 7 - Henry’s law constant for CO2 in water is 1.67x108 Pa at 298 K. Calculate the quantity of CO2 in 500 mL of soda water when packed under 2.5 atm CO 2 pressure at 298 K

Question 8- The vapour pressure of pure liquids A and B are 450 and 700 mm Hg respectively, at 350 K . Find out the composition of the liquid mixture if total vapour pressure is 600 mm Hg. Also find the composition of the vapour phase.

Question 9 -Vapour pressure of pure water at 298 K is 23.8 mm Hg. 50 g of urea (NH2 CONH2 ) is dissolved in 850 g of water. Calculate the vapour pressure of water for this solution and its relative lowering.

Question 10 -Boiling point of water at 750 mm Hg is 99.63°C. How much sucrose is to be added to 500 g of water such that it boils at 100°C

Question 11 - Calculate the mass of ascorbic acid (Vitamin C, C6 H8 O 6) to be dissolved in 75 g of acetic acid to lower its melting point by 1.5°C. K f = 3.9 K kg

mol-1.

Question 12 Calculate the osmotic pressure in pascals exerted by a solution prepared by dissolving 1.0 g of polymer of molar mass 185,000 in 450 mL of water at 37°C.