Question

25.3g of sodium carbonate is dissolved in enough water to make 250 ml of solution.if sodium carbonate dissociates completely molar concentration Of sodium ion and carbonate ion are ???

Answer 1

1) We must first find the molarity of the solute:

Referring the periodic table :
atomic mass of $Na_{2}CO_{3}$  = 105.96 g/mol (Summing inidividual atomic masses of Sodium, Carbon and Oxygen)

Number of moles of $Na_{2}CO_{3}$ = No. of grams of  dissolved $Na_{2}CO_{3}$ x ( 1 / atomic mass )

Number of moles of $Na_{2}CO_{3}$  = 25.3 x ( 1 / 105.96 ) = 0.238 mol

Now, to find number of mol $Na_{2}CO_{3}$ of  in given solution,

 = No. of moles of $Na_{2}CO_{3}$  / volume in Litres

 = 0.238 / 0.25 = 0.952 mol /L (To convert 250 ml to L we divide by 1000 as 1000 ml = 1 L)


2) Finding the number of ions :
   
  $Na_{2}CO_{3}$ → 2  $Na^{+}$ + $CO_{3}^ {--}$

So we get 2 moles of sodium and 1 mole of carbonate in 1 mol of solution of sodium Carbonate

3) Finding molarity : 

Molarity of sodium ion is = No. of moles of Sodium ion x  = 2 x 0.952 = 1.904 moles of  / Litre = 1.904 M

Molarity of Carbonate ion is = No. of moles of Carbonate ion x  = 1 x 0.952 = 0.952 moles of Carbonate ion / Litre = 0.952 M

 molar concentration Of sodium ion and carbonate ion are 1.904 M & 0.952 M respectively

Answer 2

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