1. Sample answer: Four methods of separating a mechanical mixture are sorting, settling, filtration, and dissolving.
2.a) Metals in a scrap yard can be separated by sorting.
b) Salt and sand can be separated by mixing the two substances with water. The salt will dissolve into the water, while the sand will settle at the bottom of the mixture.
c) Sand and gravel can be separated by pouring the mixture into a sieve with holes small enough to trap the gravel but large enough to let the sand through.
d) Sand and water can be separated using a filter—the water will pass through the filter but the sand will not.
3. Sample answer: The filters allow the clean air to pass through them, but they trap tiny solid particles that make the air harmful to breathe.
4. A filter is similar to a sieve in that both are used to separate mixtures by trapping larger substances in holes that allow smaller substance to pass through.
However, a filter has much smaller holes than a sieve, so that it is used to separate tiny, insoluble solids from liquids or gases. Sieves can separate larger solids from smaller solids or liquids.
