chapter 10 chemical quantities. before we begin… we need to review some scientific...
TRANSCRIPT
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.