A waste material consists of sand (SG 2.7), a chemical salt (SG 2.1), and a dense plastic (SG 1.4). 200 g of a representative sample from the material is found to have a density of 2300 kg/m3. The salt is dissolved out of the sample which, after drying, now weighs 170 g. What is the composition of the waste material?
- Based on the given information, we can derive:
densitysand = 2700 kg/m3
densitysalt = 2100 kg/m3
densityplastic = 1400 kg/m3
masssalt = 30 g = 0.03 kg
proportionsalt = 0.03 kg / 0.2 kg = 0.15
- To try and calculate the individual mass of sand and plastic in the sample, I used the density = mass / volume equation to first figure out the volume using the density and mass of the total sample.
densitytotal = masstotal / volume =
volume = masstotal / densitytotal = 0.2 kg / 2300 kg/m3 = 0.00008696 m3
masssand = 2700 kg/m3 * 0.0000869 m3 = 0.2348 kg
massplastic = 1400 kg/m3 * 0.0000869 m3 = 0.1217 kg
But I don't think this step was the right choice since the mass of the sand came out to be larger than the mass of the sample. Was I correct in trying to figure out the value of the mass of sand and plastic or was that the wrong approach to determine the material's composition? If it's the first case, how should I find out the mass values?