Decide whether a substance is pure, from melting and boiling point data. Substance Sulphur Water Melts at ° C 119 - 0 . 5 Boils at ° C 445 101

In the given data there are the melting and boiling points for two pure substances sulphur and water are given. This sulphur sample melts sharply at 119 ° C and boils at 445 ° C . So it must be pure. This water freezes around - 0 . 5 ° C and boils at 101 ° C so it is not pure. Note: A pure substance has a definite sharp melting and boiling point. They are different for each substance.

This apparatus can be used to obtain pure water from salt water. What is the purpose of cold water?

In the experiment of pure water from salt water, the cold water provides maximum cooling, therefore, allowing for maximum recovery of the purified liquid during distillation. Due to cold water, the vapours condensing them back to liquid droplets and collect into the receiver flask.

This apparatus can be used to obtain pure water from saltwater. The glass arm must reach far down into the second test tube. Why?

The glass arm must reach far down into the second test tube because when we heat saltwater as it boils, water vapour passes to the glass arm tube. The beaker is filled with water and ice; it acts as a condenser; these vapours condenses to water in it. So, if the glass arm will not reach far down, this condensing procedure will not take place faster. Water vapour colder increases the rate of condensation.