CHARACTERISTIC PROPERties

A property that helps us identify a pure substance or the group to which the pure substance belongs Two types

1. Characteristic physical properties Helps us identify a substance without changing the nature of the substance Examples: a) Boiling point - temp. at which a liquid becomes a gas (water: 100 0C) b) Melting point - temp. at which a solid becomes a liquid (water: 0 0C) c) Density – mass per unit volume (ethanol: 0.79 g/mL) d) Solubility – max amount of solute that can be dissolved in a given volume of solvent (salt in water: 357 g/L)

Phase Changes

Calculating DENSITY

Ex 1: What is the density of a rock with a mass of 20 g and a volume of 10 cm3 ? D= m D= 20g v 10 cm3 D = 2 g/ cm3

Ex. 2: What is the density of the metal rebar shown in the diagram below? V = Final volume- initial volume V = 22.4 mL – 13.5 mL V = 8.9 mL D = m = 69.658 g v 8.9 mL D = 7.8 g/ mL

Ex. 3 An empty graduated cylinder has a mass of 96. 7 g Ex. 3 An empty graduated cylinder has a mass of 96.7 g. An amount of ethanol is added until it reaches the line shown. The mass of the graduated cylinder and ethanol is 138.57 g. What is the density of ethanol?

Mass = mass of graduated cylinder and ethanol - mass of empty graduated cylinder Mass = 138.57 g – 96.7 g = 41.87 g Volume = 53 mL D = m = 41.87 g v 53 mL D = 0.79 g/ mL

Ex. If the rock from the first example was placed in the graduated cylinder form example 3, would it float or sink? Why? Sink, because the density of the rock (2 g/ cm3) is greater than the ethanol (0.79 g. mL)

2. Characteristic chemical Properties Helps us identify a substance, but the nature of the substance may change Ex. Litmus paper test: Paper turns red, then the substance is acidic (pH< 7) Paper turns blue, then the substance is basic (pH> 7) Paper turns purple, then the substance is neutral (pH=7) See Table: 1.31 p. 24 TB