UNIT 3 –Quantities in Chemical Reactions
THE MOLE!
In chemistry as in other aspects of life it is sometimes more convenient to count in groups of items rather than count items individually.
Quantity / AmountIn chemistry chemical reactions are ______.
To count the # of atoms in a chemical reaction individually is inconvenient so chemists group atoms into groups.
Chemists count in ______
______
This value is known as the ______
The mole is defined as:
______
How big is the Avogadro constant?
Try the Thought lab on pg. 175.
- Canada covers 9976140 km2
- Distance to moon is 384,403 km
- Length of $5 is 152.4 mm
- The worlds oceans hold 1.37x109 km3 water.
- One teaspoon is equal to 5ml
- Average size apple has a mass of 0.15 kg
- Mass of the Earth is 5.9742 × 1024 kg
- Current population of Earth is 6,654,181,537
Converting Moles to Number of Particles
N =
n =
NA =
Problem 1. A sample contains 2.25 moles of carbon dioxide, CO2.
a. How many molecules are in the sample?
b. How many atoms are in the sample?
Problem 2. How many moles of nitrogen dioxide are there in a sample containing 4.35 x 1024 molecules?
Molar Mass
When we measure the mass of a substance we express its mass in grams.
You have already learned that one atom of ______has a mass of exactly _____ and that ______atoms has a mass of exactly ______.
This means:
______.
This is known as ______.
Molar mass can be applied to any substance and is equivalent to the ______.
Molar mass of Al
Molar mass of HNO3 or MHNO
Using Molar Mass
The following equation will allow you to solve problems involving ______
Problem 1.
A flask contains 0.950 mol of carbon monoxide, CO. What is the mass of CO in this sample?
Problem 2.
How many moles of acetic acid CH3COOH are in a 15.2g sample?
Problem 3.
What is the mass of 6.35 x 1024 molecules of copper (II) nitrate.
Chapter 6 – Chemical Proportions in Compounds
In the late 1700’s Joseph Proust discovered that samples of copper (II) carbonate always contained the same proportion of Cu, C and O.
This led to the ______– the elements in a chemical compound are always present ______
The mass of an element in a compound, expressed as a % of the total mass is known as an elements ______.
Ex H2O
The law of definite proportions ______that the elements in compounds are always the same.
CO
CO2
If we state all of the mass percents for a compound we call it ______
A compound with a mass of 48.72g is found to contain 32.69g of Zn and 16.03g of S. What is the % composition?
Calculating % composition from a formula
Pyrite (aka ______) is a compound with the chemical formula ______. If you wanted to extract the iron and know how much to expect, you first need to know the ______.
Calculate the % composition for ______.
______C9H8O is the molecule responsible for the ______. Find the % composition of this compound.
Empirical Formula of a Compound
The ______ of a compound shows the ______of the elements in the compound.
Ex H2O2
The ______ of a compound shows the ______of each element in the compound.
The relationship between the 2 types of formulas is:
Determining Empirical Formulas
To determine an empirical formula you need to use the concepts of ______
Ex1. Calculate the empirical formula for a compound that is 85.6% C and 14.4% H.
Ex2. The percentage composition of a fuel is 81.7% carbon and 18.3% hydrogen. Find the empirical formula.
Molecular Formula of a Compound
Being able to identify unknown substances as many uses. Think forensic science.
Since many substances have the same empirical formulas, we need to be able to determine the ______for a substance. To do this we use ______.
Chemists use a ______to determine the molar mass of a substance. Then:
Ex. 1 The empirical formula for ribose (a sugar) is CH2O. The molar mass of ribose is 150g/mol (by experiment). What is the molecular formula of ribose?
Finding Formulas by Experiment
There are many ways to determine formulas by experiment.
The Carbon-Hydrogen Combustion Analyzer
This is a device used to ______.
How it works
· Stream of ______containing compounds.
· CH compound will react completely to produce ______
· All the H2O is absorbed by ______.
· Final mass – initial mass = mass of H2O. All ______.
· Use ______of H in H2O to determine mass of H
· All the CO2 is absorbed by ______. All C ends up here.
· Use ______of CO2 to determine mass of C.
· If original compound contained a third element, then:
Ex1. A 1.000g sample of a pure compound containing only C and H was combusted. 0.6919g of water and 3.338g of carbon dioxide were produced.
a. Calculate the masses of C and H in the sample.
b. Find the empirical formula of the compound.
Hydrated Ionic Compounds
Many ______crystallize from an aqueous solution, with H2O molecules ______. These are called ______.
______have a specific # of ______chemically bonded to each formula unit.
Chemical Name / FormulaCompounds that have no H2O molecules are called ______
Just remember: when doing calculations you must ______
Ex 1.
A 50.0g sample of a hydrate of barium hydroxide Ba(OH)2·xH2O contains 27.2g of Ba(OH)2.
a. Calculate the percent by mass of water in Ba(OH)2·xH2O
b. Find the value of x in Ba(OH)2.
Chapter 7 Quantities in Chemical Reactions
Stoichiometry
Stoichiometry is the study of the ______
It all begins with ______, which are essential for making calculations related to chemical reactions.
For example, the ______(used to make ammonia gas) is based on the following balanced equation:
What does this equation tell you?
1.
2.
3. If we multiply each by 12 we could say: 1 dozen molecules of nitrogen gas reacts with 3 dozen molecules of hydrogen gas to produce 2 dozen molecules of ammonia gas.
4.
The relationship between moles in a balanced chemical equation are known as MOLE RATIOS
We use mole ratios to solve problems.
1. From the equation above, how much ammonia gas would be produced from 3.5 mol of hydrogen gas?
2. When carbon and oxygen combine 2 reactions are possible. The product can be CO2 or CO.
- Write the balanced chemical equations.
- How much oxygen is needed to react with 0.75mol carbon to produce CO2?
- How much oxygen is needed to react with 0.75mol carbon to produce CO?
Mole Ratios can also be used to find the mass ratios for chemical equations.
N2(g) + 3H2(g) ® 2NH3(g)
Balanced Equation / ®# of Particles / ®
Amount / ®
Mass = n x M / ®
Total mass / ®
If you know the amount of one substance in a chemical reaction (moles, particles, mass) you can calculate the amount of any other substances in the reaction using the ______.
Solving Stoichiometric Problems
Follow this process:
1.
2.
3.
4.
Ex 1. Mass to Mass
Astronauts must be able to remove the CO2 from their spacecraft. If not hypoxia (lack of O2) would occur. CO2 is removed using the following chemical reaction: CO2(g) + 2LiOH(s) ® Li2CO3(g) + H2O(g) . If an astronaut produces 1.50x103 g of CO2 a day, what mass of LiOH would be needed per day?
Ex 2. On Feb, 20, 2008 the US Navy shot down a spy satellite in space from a war ship in the Pacific ocean. They claimed the satellite contained hydrazine (rocket fuel), that could harm people if the satellite fell back to Earth. When hydrazine is combined with dinitrogen tetroxide it produces nitrogen gas and water. If 100g of hydrazine is reacted, how much nitrogen gas would be produced?
Ex 3. During WWI, chlorine gas was used as a weapon. When chlorine gas enters the lungs it reacts with water and forms corrosive hydrochloric acid and oxygen gas. How many molecules of chlorine react to produce 5.0g of HCl?
The Limiting Reactant/Reagent
Chemical reaction equations give the ideal ______. However, the reactants for a reaction in an experiment are not necessarily a ______.
In a chemical reaction, one of the reactants may ______when the reaction is finished. These are called ______. The reagent that is ______or reacted is called the ______, because its quantity limit the amount of products formed.
Think of when you put gas in your car:
2C8H18 + 25O2 ® 16CO2 + 18H2O
Ideally, ______of oxygen react with ______of octane. But in reality ______so ______would be the ______. When you run out of gas ______
In stoichiometric problems, ______
Ex 1. Glucose reacts with oxygen gas to produce carbon dioxide and water during cellular respiration. If 1.25 g of glucose reacts with 7.51g of oxygen gas, find the limiting reactant.
Now that you know the limiting reactant above, how much carbon dioxide would be produced?
Ex 3. Iron and carbon dioxide can be produced when iron(III) oxide reacts with carbon monoxide gas. If 11.5 g of iron(III) oxide is reacted with 2.63x1024 molecules of carbon monoxide, what mass of iron is expected?
Percentage Yield
Chemists use ______to predict the ______that can be ______from a chemical reaction.
This amount is called the ______.
This amount is ______. The ______obtained in an experiment is called the ______.
The ______is usually less then the ______and for a variety of reasons. For example:
______compares the ______(actual) to the ______(theoretical).
Ex 1. When 75g of nitrogen gas reacts with sufficient hydrogen gas, the theoretical yield of ammonia is 9.10g. If 1.72 g of ammonia is obtained what is the percentage yield?
Ex 2. When Calcium carbonate is decomposed to calcium oxide and carbon dioxide there is a 92.4% yield of calcium oxide. How many grams of calcium oxide can you expect if 12.4g of calcium carbonate is heated.
Many times substances may not be pure. The substance might contain ______. If gold is 99% pure then it must contain 1% other substances. ______describes what proportion of a sample is composed of a specific compound or element.
Ex 1. You have a 13.9 g sample of “fools gold”. You heat the sample in oxygen and produce 8.02g of iron (III) oxide. What % purity of iron pyrite was in the original sample?
4FeS2 + 11O2 ® 2Fe2O3 + 8SO2