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 Amount In 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 km 2 - Distance to moon is 384,403 km - Length of $5 is 152.4 mm - The worlds oceans hold 1.37x10 9 km 3 water. - One teaspoon is equal to 5ml - Average size apple has a mass of 0.15 kg - Mass of the Earth is 5.9742 10 24 kg - Current population of Earth is 6,654,181,537 Converting Moles to Number of Particles N = n = N A = Problem 1. A sample contains 2.25 moles of carbon dioxide, CO 2. 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 10 24 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 HNO 3 or M HNO 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 CH 3 COOH are in a 15.2g sample? Problem 3. What is the mass of 6.35 x 10 24 molecules of copper (II) nitrate. Number of Particles Moles Mass of substance
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 H 2 O The law of definite proportions that the elements in compounds are always the same. CO CO 2 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.
C 9 H 8 O 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 H 2 O 2 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 CH 2 O. 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 H 2 O is absorbed by. Final mass initial mass = mass of H 2 O. All. Use of H in H 2 O to determine mass of H All the CO 2 is absorbed by. All C ends up here. Use of CO 2 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 H 2 O molecules. These are called. have a specific # of chemically bonded to each formula unit.
Chemical Name Formula Compounds that have no H 2 O 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 xh 2 O contains 27.2g of Ba(OH) 2. a. Calculate the percent by mass of water in Ba(OH) 2 xh 2 O 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 CO 2 or CO. a. Write the balanced chemical equations. b. How much oxygen is needed to react with 0.75mol carbon to produce CO 2? c. 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. N 2(g) + 3H 2(g) 2NH 3(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 CO 2 from their spacecraft. If not hypoxia (lack of O 2 ) would occur. CO 2 is removed using the following chemical reaction: CO 2(g) + 2LiOH (s) Li 2 CO 3(g) + H 2 O (g). If an astronaut produces 1.50x10 3 g of CO 2 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: 2C 8 H 18 + 25O 2 16CO 2 + 18H 2 O 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 2.63x10 24 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: a. b. c. d. 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? 4FeS 2 + 11O 2 2Fe 2 O 3 + 8SO 2