1.4 Composition of Mixtures

When two or more pure substances (elements or compounds) are combined they form a:

mixture

In mixtures, composition stays the same / varies

varies

A mixture can be analyzed in order to determine the:

mass composition of each substance in the mixture

You can use ______ to convert the masses of the products from the analysis to find the amounts of reactants that were in the original mixture.

stoichiometry (mole ratios)

How to calculate mass percentage of a substance in a mixture?

mass of substance / total mass of mixture x 100

Elemental Analysis to determine the composition of a mixture can be:

qualitative (identify the different elements present) or quantitative (identify the amounts of elements present.)

Elemental analysis is a part of ______ chemistry

analytical

Examples of elemental analysis:

CHNX and Spectroscopy

CHNX is used to identify:

mass fractions of carbon, hydrogen, nitrogen and other atoms such as halogens or sulfur.

One form of CHNX is:

Combustion analysis

What happens in combustion analysis?

All of the carbon in a sample is converted into carbon dioxide, all of the hydrogen is converted into water, nitrogen is converted into nitrogen monoxide or nitrogen dioxide and sulfur (for example) is converted into sulfur dioxide.

3 types of spectroscopy:

Optical, mass, and photoelectron

Process of optical spectroscopy:

light is passed through a colored solution and the amount of light absorbed or transmitted is measured to determine the concentration of the solution

Process of mass spectroscopy:

The charge to mass ratio is measured by atomizing then ionizing a sample, then accelerating the sample between charged plates and measuring the deflection of the sample.

In mass spectroscopy, greater deflection is found in:

smaller masses or larger charges

Photoelectron spectroscopy

The energy to remove electrons from atoms is measured and can be translated into the electron configuration (arrangement) for an element.