Ist year Chemistry : Exercies Short Question Chapter 1 -------- Malik Xufyan

Ist year Chemistry : Exercies Short Question Chapter 1 --------------- Malik Xufyan

Q8:      Justify the following statements:
(a)        23 g of sodium and 238g of uranium have equal number of atoms in themAns :
(a)        23g of Na        =1 mole of Na             =6.02x1023 atoms of Na
            238g of U        =1 mole of U               =6.02x1023 atoms of U.
            Since equal number of gram atoms(moles) of different elements contain equal number of atoms. Hence, 1 mole (23g ) of sodium and 1 mole (238)g of uranium contain equal number of atoms , i , e ,6.02x1023 atoms.  
(b) Mg atom is twice heavier than that of carbon.Ans:
    Since the atomic mass of Mg (24) is twice the atomic mass of carbon (12) therefore, Mg atom is twice heavier than that of carbon. Or
Mass of 1 atom of Mg= 24
Mass of 1 atom of C    = 12
Since the mass of one atom of Mg is twice the mass of one atom of C, therefore, Mg atom is twice heavier than that of carbon.
(c)        180g of glucose and 342 g of sucrose have the same number of molecules but different number of atoms present in them.Ans:
 180 g of glucose = 1 mole of glucose =6.02x1023 molecules of glucose 342 g of sucrose=1mole of sucrose    =6.02x1023 molecules of sucrose
Since one mole of different compounds has the same number of molecules.
 Therefore  1 mole (180g) of glucose and I mole (342g) of sucrose contain the same number (6.02x1023)of molecules. Because one molecule of glucose, C6H12O6 contains 45 atoms whereas one molecules of glucose, C12 H22 O11 contains 24 atoms. Therefore, 6.02x1023 molecules of glucose contain different atoms as compound to6.02x1023 molecules of sucrose. Hence, 180 g of glucose and 342g og sucrose have the same number of molecules but different number of atoms present in them.
(d)        4.9g of H2 SO4 when completely ionized in water , have equal number of positive and negative charges but the number of positively charged ions are twice the number of negatively charged ions.,Ans:            H2 SO4  <------>  2H+ + SO4-2
            When one molecules of H2 SO4 completely ionizes in water it produces two H+ ion and one SO ion,. Hydrogen ion carries a unit positive charge whereas SO ion carries a double negative charge. To keep the neutrality, the number of hydrogen are twice than the number of soleplate ions. Similarly the ions produced by complete ionization of 4.8g of H2 SO4 in water will have equal number of positive and negative but the number of positively charged ions are twice the number of negatively charged ions.
(e)        One mg of K2 Cr O4 has thrice the number of ions than the number of formula units when ionized in water.   Ans:
K2Cr2O7..........>   2k+ + Cr2O7-2
     K2 Cr O4 when ionizes in water produces two k+ ions one C O  ion. Thus each formula unit of K2 Cr O4produces three ions in solution .Hence one mg of K2 Cr O4 has thrice the number of ion than the number of formula units ionized in water.
(f)        Two grams of H2 , 16 g of ch4 and 44g of CO2 occupy separately the volumes of 22.414 dm3 , although the sizes and masses of molecules of three gases are very different from each other.Ans:
       2g of  H2 =1 mole of H2 =6.02x1023 molecules of H2 at STP =22.414dm3 16g of CH4 =1mole of CH4 =6.02x1023 molecules of CH4 at STP =22.414dm3 144g of CO2 =1mole of CO2 =6.02x1023 molecules of CO2 at STP =22.144dm3
            Although H2 , CH4 and CO2 have different masses but they have the same number of moles and molecules . Hence the same number of moles or the same number of molecules of different gases occupy the same volume at STP. Hence 2 g of H2 ,16g of CH4 and 44 g of CO2 occupy the same volume 22.414 dm3 at STP. The masses and the sizes of the molecules do not affect the volumes