Unit 5: Mixtures and Impurities

Substances can be made by elements, compound or mixtures.

Element

  • An element is the simplest substance that consists of only one type of atom

  • It can be in the form of atoms or molecules

  • Compounds

Compounds

  • Chemical substances made up of 2 or more elements that are chemically bounded together in a fixed ration.

  • A mixture of iron and sulfur heated together is equal to a chemical reaction that forms iron sulfide

Mixture

  • A mixture contains of 2 or more pure substances (elements or compounds) which and not chemically bounded together.

    1.8 Elements, compounds, mixtures – Chemistry

What are Reactants

  • A substance that takes part in change during a chemical reaction

Purity and Pure Substances

  • A substance is said to be pure if it only contains one kind of element or one type of compounds

  • A pure substance has an definite melting and boiling point

Impurities and Impure Substances

  • For the substances that contain a mixture of elements, a mixture of compounds, or a mixture of both elements and compounds.

Causes of Impurities

  • Sometimes not all of an reactant is used up, and this becomes a impurity among the products

  • At room temp, lots of reactants that do not react on time are left behind

  • Reactants may carry impurities with it already


Basic chemical reactions:

  • Equations are used to describe chemical reaction

  • Substances that take part in a reaction is called the reactants

  • Substances that form as a result are the products

  • Reactants -> products

  • Calculating purity:

  • % purity = mass of substance in the sample * 100% Mass of the sample

Dissolution:

  • The process where a solute in an state dissolved in a solvent to form a solute

Concentration:

  • More solute particles dissolved in the same volume = more concentrated

Solute

  • The Solid/Liquid/Gas

  • The substance that dissolved in a liquid to or a solution, usually a solid (e.g. The salt in the sea water)

Solvent

  • The liquid

  • The liquid in which a solute dissolves (E.g. The water in the sea water)

Solution

  • Solute + Solvent = Solution

  • The mixture formed when a solute has dissolved in a solvent (E.g. Sea water)

Solubility

  • The maximum amount of solute that can dissolve in a certain volume of solvent certain temperature

  • Can be affected by temp or different substances in the same solvent

Soluble

  • Describes a gas or solid that dissolves in a solvent (E.g.. Salt is soluble in water)

Insoluble

  • Describes a gas or solid tat does not dissolve in a solvent (e.g.. Sand is insoluble in water)

Chromatography

  • Used to separate mixtures for analysis

  • A mixture (such as ink) will separate in a solvent (such as water) into its comp producing as many spots as components

  • If it is pure, it will produce just one spot.

Paper Chromatography

1. Draw a pencil line across a strip of chromatography paper near one end (2cm The pencil line does not dissolve in the solvent

2. Place a solvent in a beaker, it must be lower than the pencil mark

3. Put one end of the strip in the beaker and leave it for a while

4. The paper absorbs the solvent and draws it up the strip

Since different solutes have different solubilizes, they move up at a different speed

The most solvable pigment will move up the furthest, vice-versa

A solute will move up to the same position no matter which sample it is in, as long as the solvent used is the same

Rf Values

  • Used to measure the distance moved by the solvent and the distance moved by a substance

  • This is a ratio called Rf Value

  • Rf = distance moved by substance

  • Distance moved by solvent