Pure Substances Flashcards

All 5 cards in this deck

What is a pure substance in chemistry?

A single element or compound, not mixed with any other substance.

In everyday language, what does it mean to call something 'pure', e.g. pure milk?

Nothing has been added to it — it is unadulterated and in its natural state.

How do the melting and boiling points of a pure substance differ from those of a mixture?

A pure substance melts and boils at specific (fixed) temperatures; a mixture melts and boils over a range of temperatures.

What are the steps to use melting point data to decide whether a solid is pure?

e.g. a white solid melts between $52\,^\circ\text{C}$ and $58\,^\circ\text{C}$

1. See whether it melts at one specific temperature or over a range: it melts over a range, $52$–$58\,^\circ\text{C}$
2. A range of temperatures means impure; a single specific temperature means pure: so the solid is impure (a mixture)
3. If it were pure, compare its melting point with data book values to identify it.

True or false? A mixture of two pure compounds is still a pure substance.

False. A pure substance must be a single element or compound; any mixture is impure.