Q.

1 gram of sodium hydroxide was treated with 25 mL of 0.75 M HCl solution, the mass of sodium hydroxide left unreacted is equal to               [2024]

1 750 mg  
2 250 mg  
3 zero mg    
4 200 mg     

Ans.

(2)

Molarity =MolesVolume (mL)×1000

For HCl,

Number of moles =M×V(mL)1000=0.75×251000=0.7540

Mass of HCl reacted =0.7540×36.5=0.684g

According to balanced equation

NaOH1 mole (40 g)          +             HCl1 mole (36.5 g)NaCl+H2O  

36.5 g HCl reacts with 40 g NaOH

0.684 g HCl will react with 4036.5×0.684=0.75g

NaOH left unreacted =1-0.75=0.25g or 250mg