CHAPTER 10

Chemical Quantities

Before We Begin…

We need to review some scientific notation.

Scientific notation is a way of writing very large and very small numbers.

How to Write Numbers in Scientific Notation

Always written as a coefficient multiplied by 10 raised to a power.

3.5 x 1034

coefficient

power

How to Multiply in Scientific Notation

To multiply numbers written in scientific notation you multiply the coefficients and add the powers.

(2.35x1014) x (3.25x10-

23)Multiply Add

Answer = 7.64x10-9

How to Divide in Scientific Notation

To divide numbers written in scientific notation you divide the coefficients and subtract the powers.

(2.35x1014) ÷ (3.25x10-23)Divide Subtrac

tAnswer =7.2x1036

The Mole: A Measurement of Matter

Section 1

Measuring Matter

You often measure the amount of something by one of three different methods – by count, by mass, and by volume.

What Is a Mole?

Mole (mol) – 6.02x1023 representative particles of that substance (SI unit for measuring the amount of something).

Avogadro’s number - 6.02x1023 named after Amadeo Avogadro di Quarenga (1776-1856)

A mole of any substance contains Avogadro’s number of representative particles, or 6.02x1023 representative particles.

The Mass of a Mole of an Element

The atomic mass of an element expressed in grams is the mass of a mole of the element.

Molar mass – the mass of a mole of an element.

Find the element on the periodic table and the mass that’s listed is the mass of one mole.

The Mass of a Mole of a Compound

To calculate the molar mass of a compound, find the number of grams of each element in one mole of the compound.

Then add the masses of the elements in the compound.

How Big is a Mole

Mole-Mass and Mole-Volume Relationships

Section 2

The Mole-Mass Relationship

Use the molar mass of an element or compound to convert between the mass of a substance and the moles of a substance.

The Mole-Volume Relationship Avogadro’s hypothesis – states that

equal volumes of gases at the same temperature and pressure contain equal numbers of particles.

Standard temperature and pressure (STP) – means a temperature of 0°C and a pressure of 101.3kPa or 1 atmosphere (atm).

At STP, 1 mole or 6.02x1023 representative particles, of any gas occupies a volume of 22.4L

Molar volume – the 22.4L of a gas.

Percent Composition and Chemical Formulas

Section 3

The Percent Composition of a Compound

Percent composition – the percent by mass of each element in the compound.

The percent by mass of an element in a compound is the number of grams of the element divided by the mass in grams of the compound, multiplied by 100%

Percent Composition from Mass Data

Can calculate by thinking part over a whole times 100%

Percent Composition as a Conversion Factor

Once you know the percent composition you can say that in a 100g sample you have that percent in grams of that element.

Example:

Propane is 81.8% carbon so in a 100g sample you have how many grams of carbon that you can use this as a conversion factor?

Empirical Formulas

Empirical formula – lowest whole-number ratio of the atoms of the elements in a compound.

For example HO is an empirical formula for H2O2 (peroxide).

Using percent compositions you can determine empirical formulas.

Molecular Formulas

The molecular formula of a compound is either the same as its experimentally determined empirical formula, or it is a simple whole-number multiple of its empirical formula.