Ghazal

گٹہ او تاوان سره تڑلی دی .
وصل او ھجران سره تڑلی دی .
کلہ بہ خواشی کلہ بہ غم رازی .
دواڑا دا انسان سره تڑلی دی .
زیڑ ماز دیگرے او دا جانان دیدن.
دا مے دا ارمان سره تڑلی دی .
یار دے کہ رقیب دے او کہ زۂ یمہ.
دغہ درے کسان سره تڑلی دی.

Atoms Molecules Elements and Compounds

   An atom capable of independent existence, or group of atoms bonded by covalent bond is called a molecule. Eg He, Ne, H2, O2,  C, H2O, S, H2O, H2SO4 etc.
  If in a molecule all the atoms are chemically identical, then it is called an element. Eg He, Ne, H2, C, S etc.
  If a molecule is made up of different atoms then its called a compound. Eg H2O, H2SO4 and NaOH etc.
  Metals are elements since here all the atoms are chemically identical. Eg Na, K, Rb etc but not molecules because they don't have covalent bonds. Nor their atoms are capable of independent existence. They have a special type of bonding called metallic bond.
  Group of ions (bonded by ionic bond) are called ionic compounds, eg NaCl, MgCl2 etc. They are compounds because the atoms (ions) are not same but not molecules because they don't have covalent bonds.
  Atoms are the building blocks of all matter, mixture, molecules, elements and compounds. And molecules are the building blocks of elements and compounds.
  If we say H2 is a compound then carbon will also be a compound which is not the case.

Leveling effect

In aqueous solution all very strong bases like Na+H–, Na+NH2–, Na+OC2H5– are levelled to the strength of OH– ion, for they react completely with H2O to produce OH–ions. In other words, they are stronger bases than the conjugate base OH-.
Na+H- +HOH = OH-  + NaH2+
So bases stronger than the conjugate base of the solution are levelled  (behave of equal strength ) and this effect is called leveling effect or solvent effect.

Similarly
  Since HF and HCl both are ~ 100% ionised in liquid NH3 to give ~100% NH4+ ions, these appear to be of equal strength and liquid NH3 acts as a levelling solvent for HF and HCl. In H2O, HF is only partially ionised, whereas HCl and HBr are ~ 100% ionised. So H2O is a differentiating solvent for HF and HBr/HCl. In other words, HF and H3O+ are of about equal strength acids. And HCl/HBr are  stronger  acids  than H3O+.

        HF+NH3=NH4+ +F-
         0               100
        HBr/HCl+NH3=NH4+  +Cl-
         0               100

        HF+H2O =H3O+  +F-
        45               55
       HBr/HCl+H2O =H3O+  +Cl-
         0                  100
     
 The solvents in which complete proton-transfer occurs are called levelling solvents?
  In other words, the solvent in which the solute is ~100% ionised, are called levelling solvents.
  Thus H2O is a differentiating solvent for HF and HCl, but for HCl and HBr it is a leveling solvent. Several mineral acids are partially ionised in glacial CH3COOH medium because CH3COOH is a poor proton-acceptor but rather a better proton donor. CH3COOH, therefore, acts as a differentiating solvent towards the mineral acids. But, for bases, CH3COOH act as a leveling solvent.

  CH3COOH+H+=CH3COOH2+  Poor
                                                 (weaker base)
  CH3COOH=CH3COO- +H        Good
                                                (stronger acid)
  HCl+CH3COOH = CH3COOH2+ +Cl-
    10                              90
  HBr
   15                                85 (suposed figures)
  HF
   20                                80

 NaOH+CH3COOH = CH3COONa+ H2O
     0                                  100
  KOH
     0                                   100
     This phenomenon viz the strength of all acids becomes equal to that of H3O+ion is called leveling effect of the solvent, and here water is called a leveling solvent for all these acids.

Solubility

The grams of solute that makes a saturated solution with 100 grams of a solvent is called its solubility. eg if 15 grams of sugar can dissolve in 100 grams of water at most then 15 grams is the solubility of sugar.

  Determination of Solubility
Take some amount (more than 100 grams)of a solvent. Start dissolving the test solute till no more of it dissolves. This means that we have reached a saturated solution. Now filter the solution to remove the undissolved solute. Weigh the filterate. Say it is 125 grams. Now boil out the solvent. Weigh again the solid solute left. Say it is 30 grams. From this we can calculate the weight of the solvent,
 125-30=95 grams. Now we can calculate the solubility of the test solute.

  95g of solvent dissolved 30g  of solute
  100g of solvent'll dissolve Xg of solute

    X=100×30÷95=31.6g

So the solubility of the given solute is 31.6 grams.

 Note: If the solute particles can be solvated by the solvent particles, the solute is said to be soluble in the given solvent. Solubility is achieved by ion-dipole or dipole -dipole interaction between solute and solvent or through the dielectric constant of the solvent. For example alcohols are soluble in water through H bonding a dipole dipole phenomenon and NaCl is soluble in water through ion dipole method.

 If the No. of solute particles exceeds than the solvent particles, then the solution is said to be saturated.

 Oils are insoluble in water because their particles can't be separated/solvated by water. We can force them temporarily but after awhile they mutually coagulate. There is no way for water molecules to trap them ie through its polarity or dielectric constant.
 Glucose, a monosaccaride is soluble in water by HB method where by water takes apart/solvate individual glucose molecules, C6H12O6 , and surrounds it through its molecules, H2O . Same is the case with oligosaccarides like sugar C12H22O11.
 But polysaccharides are unsoluble in water because there we don't have individual particles to be solvated and thus broken apart by water although the also have OH groups like the previous saccarides for HBonding with water. It is because they are actually strands of molecules called polymers. Although water does make HB but can't solvate/isolate individual particles, molecules. They are polymers like (C6H12O6)n.

Why Mono and Oligosaccarides are Soluble in Water but not Polysaccharides?

The breaking apart of solute particles by solute is called solubility. For example when NaCl is put in water it is broken into Na ans Cl particles. Water break them apart by surrounding each through its molecules H2O by ion dipole method.
 Oils are insoluble in water because their particles can't be separated by water. We can force them temporarily but after awhile the mutually coagulate.
 Glucose, a monosaccaride is soluble in water by HB method where by water takes apart individual glucose molecule, C6H12O6 , and surrounds it through its molecules, H2O . Same is the case with oligosaccarides like sugar C12H22O11.
 But polysaccharides are unsoluble in water because there we don't have individual particles to be taken apart by water. They are actually strands of molecules called polymers. Although water does make HB but can't isolate individual particles, molecules. They are polymers like (C6H12O6)n.
 We can fore solubility. Eg alloys. Where we dissolve a solid in solid. Although ordinarily we cant say that solid is soluble in solid.
 But actually solubility is the dissolution of some thing gas liguid or solid in a liquid.