Chemistry - moles

Chemistry - MolesA Demonstration to describe the concept of moles more briefly.

Part 1: Chemical Quantities

Introduction

● How did you determine the number of M&Ms in the bag without actually counting?

Atoms

● Can you determine the number of atoms of an element even though you can not actually count them?

● Yes… IF there is a conversion factor that allows you to convert between mass and number of atoms.

Moles

● The SI base unit that measures amount of substance

● Avogadro’s Number:6.02 x 1023 atoms

Moles and Atomic Mass

● The atomic mass of an element in grams contains one mole of atoms (Avogadro’s number of atoms)

● Example: There are 6.02 x 1023 (or 1.0 moles) of atoms in 12.011 g of carbon

Moles as Conversion Factors

● Use moles/grams (or grams/moles) as a conversion factor

● Ex: 16.0 g oxygen -----------------------------

1 mole oxygen

Example 1

● How many moles of helium atoms are in 6.8 grams?

Example 2

● How many grams is equal to 1.51 moles of iron?

Examples 3, 4, and 5

● 17.6 grams of chlorine is equal to how many moles?

● How many moles of nickel do you have if you have 65.1 g?

● React 1.9 moles of sodium with chlorine gas to get sodium chloride. How many grams of sodium do you need?

Calculating Molar Mass

● Atomic Mass of an element = “molar mass”

● Molar mass of a compound must be calculated

Calculating Molar Mass

● How many oxygens are in a DOZEN water molecules?

● How many hydrogens?

Calculating Molar Mass

● One mole of WATER MOLECULES (H2O) is one mole of oxygen atoms and two moles of hydrogen atoms

● Calculate the mass of one mole of water molecules

Calculate the molar mass of…

● Boron Trifluoride

● Sodium Iodide

● Sodium Bicarbonate (NaHCO3)

● Glucose (C6H12O6)

● Copper (III) Sulfate

REMEMBER!

● Molar mass is the mass of one mole of an element/compound.

● Molar mass has units of grams/mole.

● Molar mass can be used as a conversion factor to find grams or find moles.

What you should know so far:●Explain the concept of a “mole” and give a definition

●Explain how one mole of an element is related to atomic mass

●Find the molar mass of an element (using correct units)

●Determine the number of grams/moles of a given element using molar mass

●Calculate the molar mass of a compound

●Determine the number of grams/moles of a given compound using molar mass

Making A Solution

● You want to make a solution by dissolving 4.00 moles of potassium nitrate in water. How many grams of the compound will you need?

Example!

● Calculate the number of moles in a 13.8-g sample of butane lighter fluid. The formula for butane is C4H10.

Find the mass of:

●0.702 mol Be.

●2.40 mol N2.

●0.160 mol H2O2.

●5.08 mol NaNO3.

Find the numberof moles.

●187 g Al

●0.264 gLi2HPO4

●333 g SnF2

● How many grams are in 5.66 mol of CaCO3?

● How many moles are in 508 grams of ethanol, CH3CH2OH?

Part 2: Moles of a Gas

Gases

● Solids/liquids are packed tightly together and more space is needed if atoms/molecules are larger

● Atoms/molecules in gases are far apart, so larger atoms/molecules do not need more space

Mole-Volume Relationship

● Avogadro’s Hypothesis – equal volumes of gases contain equal numbers of particles

● 1 mole of any gas takes up the same volume as long as…

STP

● …as long as the gases are at the same pressures and temperatures

● STP, or “standard temperature and pressure” means 0oC and 1 atmosphere, which is air pressure at sea level

Calculating Moles of a Gas

● At STP, a mole of any gas takes up 22.4 liters.

● Use 22.4 L/mol as a conversion factor!

Example 1

● How many liters will a 0.19-mole sample of oxygen gas take up?

Example 2

● A blimp has a volume of 95 kL (95,000 L). If it is filled with helium at STP, how many moles of the gas are contained within the blimp?

Examples 3 and 4

● Find the number of moles in a sample of chlorine gas stored in a 14.2-liter tank at STP.

● What is the volume of 0.18 moles of xenon at STP?

During Last Week’s Episode…

● Look up molar mass of elements / calculate molar mass of compounds

● Convert moles-grams using molar mass as the conversion factor (elements and

compounds)

● Convert moles-liters of a gas using molar volume (22.4 L/mol)

MOLES

Mass (g)

Volume (L) # Atoms

Conversion Factor: molar mass

Conversion Factor: molar volume(22.4 L / 1 mol)

Conversion Factor: Avogadro’s number

6.02 x 1023 atoms/mol

Challenge Problem

● Calculate the mass of 16.4 L of chlorine gas at STP.

Part 3: Molarity

Molarity

Molarity is a measure of how concentrated a solution is

Amount of solute per volume of solution

High concentration / high molarity

MolarityMeasured in units of moles/liter

mol/L = “M”

A 2.5 M solution has 2.5 moles of salt in one liter of water

Molarity Problems

To make one liter of a 2.5 molar solution of sodium chloride, how many grams of sodium chloride do you need?

Molarity Problems

SET MOLARITY PROBLEMS UP AS A PROPORTION!

●How many moles of silver nitrate (AgNO3) are in 0.4 L of a 6.0 M solution?

●How many grams of silver nitrate is that?

Molarity Problem #3

How many grams of lead(IV) chloride must be dissolved in 50 mL of water to make a 0.1 M solution?

Remember: 0.1 M = 0.1 mol/L

Molarity Problem #4

●If you dissolve 56 g of sugar (sucrose, C12H22O11) into a liter of water, what is the molarity of the solution you created?

Part 3: Percent Composition

Section 10.3, page 305

● Methane, CH4, is made of solely hydrogen and carbon. What percent of the compound is hydrogen? What percent is carbon?

Percent Composition

● Remember that some atoms are larger, by mass, than others

● Mass of each atom must be taken into account when calculating percent composition

Percent Composition

● Percent composition = % (by mass) of each atom in a compound

mass of element% composition = --------------------------- x 100%

mass of compound

Example 1

● 15.1 grams of oxygen combine with 1.9 g of hydrogen to make water. Find the percent composition of each element.

Example 2

● A sample of glucose is synthesized from 58.00 g carbon, 9.73 g hydrogen, and 77.27 g oxygen. Find the percent composition for each element.

Percent Composition and Chemical Formulas

● Allows you to find the %composition of an elementin a compound withoutknowing the mass of thatelement

molar mass of element% composition = --------------------------------------- x 100%

molar mass of compound

Example 1

● What percentage of a sample of table salt, sodium chloride, is sodium?

Example 2

● Determine the percent composition of iron (III) oxide.

Example 3

● Hypochlorous acid is one of the active sanitizers in pool-cleaning products. Its formula is HClO. What percent of the compound is oxygen?

Using Percent Compositionto Calculate Mass

● To calculate mass of one element in a specific mass of a compound, multiply the mass of the compound by the percent composition of that element.

Using Percent Compositionto Calculate Mass

● Example:

● Carbon is 27.3% of CO2. Of 45.1 g of CO2, what mass is carbon?

27.3% x 45.1 g = 12.3 g

Example 1

● Find the number of grams of sodium in 10.1 g of sodium sulfate.

● HINT! First write the formula for sodium sulfate, then find the % sodium.

Thank You

A Presentation by Irfad Imtiaz

Stay Tuned

Facebook.com/IrfadImtiazTwitter.com/IrfadImtiazSlideshare.net/IrfadImtiazhttp://www.irfadimtiaz.com