A concentration of 1g DDT per 10 dm^3 fo water can prove to be toxic for some living organisms. How many ppm is this?
Is the formula to estimate ppm:
ppm (solute) = [mass of the solute (mg) / volume of the solution (dm^3)] x 100
Parts per million is abbreviated as ppm. For illustration if there are 2 g of a compound A in a mixture of A and B with a mass 1000 kg, there are 2 ppm of A in the mixture.
DDT is the abbreviated chemical name of a pesticide widely used in the past, the use of this compound is being strongly discouraged due to its harmful effects on human health and in other ways that it damages the environment. DDT stands for dichloro-diphenyl-trichloro-ethane.
The density of water is 1000 kg/m^3. 1 dm^3 is 1/100 of a m^3. The mass of 1 dm^3 of water is 1000/100 = 10 kg. 10 dm^3 of water has a mass of 100 kg. 100 kg is equal to 100*1000 = 10^5 g
1 g of DDT in 10 dm^3 of the solution is 10^6/10^5 = 10 ppm.
The formula given in your book is correct. Substituting the values given in the problem the formula yields 10 ppm.