A sample of drinking water was found to be severely contaminated with chloroform, `CHCl_3` supposed to be carcinogenic in nature. The level of contamination was 15 ppm (by mass).
Express this in percent by mass.

A sample of drinking water was found to be severely contaminated with chloroform, CHCl_3 supposed to be carcinogenic in nature. The level of contamination was 16 ppm (by mass). Determine the molality of chloroform in the water sample.

A welding fuel gas contains carbon and hydrogen only. Burning a small sample of it in oxygen gives 3.38 g carbon dioxide, 0.690g of water and no other products. A volume of 10.0L (measured at STP) of this welding gas is found to weigh 11.7 g. Calculate molar mass of the gas