A sample of drinking water was found to be severely contaminated with chloroform (CHC13) supposed to be a carcinogen. The level of contamination was 15 ppm (by mass): determine the molality of chloroform in the water sample.

6.2g of a sample containing Na_2CO_3, NaHCO_3 and non-volatile inert impurity on gentle heating loses 5% of its mass due to reaction 2NaHCO_3 rarr Na_2 CO_3 + H_2 O + CO_2 . Residue is dissolved in water and formed 100mL solution and its 10mL portion requires 7.5 mL of 0.2M aqueous solution of BaCI_2 for complete precipitation of carbonates. Determine mass (in gram) of Na_2 CO_3 in the original sample.

A 1.025 g sample containing a weak acid HX (mol. Mass=82) is dissolved in 60 mL. water and titrated with 0.25 M NaOH. When half of the acid was neutralised the pH was found to be 5.0 and at the equivalence point the pH is 9.0. Calculate mass precentage of HX in sample :