Chemistry Module I Lesson 6: Stoichiometry

What is the molecular mass of a compound and how would you find the percent of an individual atom in a compound?

The sum of all the masses of the atoms in the compound. You take the sum of the mass of the atom and divide it by the total compound mass giving you the percent the element makes up of the compound.

True/False? If all the reactants are used up in a chemical reaction to form a product, then they are all considered the limiting reagents.

True

What is the likely empirical formula if you have 100 grams of a molecule containing, 73% Hg and 27% Cl?

You will have 27g Cl and 73g of Hg 1 mol Cl = 35.453g 1 mol Hg = 200.59g So, 73g Hg = 73/200.59 moles Hg = 0.364 mol Hg 27g Cl = 27/35.453 mols Cl = 0.762 mol Cl Hg Cl2

What is the concept of equivalents?

how many moles will a given compound produce of a particular subject of interest (i.e. protons, electrons, hydroxide ions, ions).

What law states that any pure sample of a given compound will contain the same elements in an identical mass ratio.

the law of constant composition ex. 1 sample of water will contain 2 hydrogen atoms for every 1 oxygen. or for every one gram of hydrogen, there will be eight grams of oxygen.

What is the mass of 1 mole of Aluminum? (Where you find the number)

the mass number with grams as units off the periodic table.

Given the chemical reaction, Fe2O3 + Al = Al2O3 + Fe, How many grams of Aluminum do we need if we are given 85 grams of Fe2O3?

1. Balance the equation: Fe2O3 + 2Al = Al2O3 + 2Fe Now, we can see for every 1 mol of Fe2O3 we have 2 Al. 2. Find how many moles of Fe2O3 we have if given 85 grams of Fe2O3. so, (56*2)+(16*3) = 160 amu of 1 molecule so, 1 mole of Fe2O3 = 160 grams. 85 grams =85/160 = .53 mols. If we have .53 moles of Fe2O3 we need 2x Al finding we have 1.06 moles of aluminum 1 Al = 27 amu :: 1 mole of Al = 27g finally, 1.06 moles of Al = 1.06*27g = 28.6g of Al to use up all Fe2O3.

How many molecules of H2O are in 20 grams of H2O?

20 g H2O/18g/mol = 1.11 moles of H2O (6.022e323 atoms/mole)(1.11 moles of H2O) = 6.68e23 m

What is the normality of 2 M H3PO4?

3 equivalents of H+ and 2 mol/L = 6N

What kind of reaction forms a new compound as the product, when the reactant compound reacts.

A chemical reaction Ex. Redox, combination, addition, combustion of hydrocarbons, etc.

What is a mole and its value?

A mole (n) of a substance or a mole of particles is defined as exactly 6.02214076×10²³ particles, which may be atoms, molecules, ions, or electrons. That is Avogadro's number.

NH3(g) + O2(g) = NO(g) + H2O If you are given 34g of NH3(g) and 32g of O2(g), how many grams of NO are produced?

Balanced: (NH3(g) + 5/4 O2(g) = NO(g) + 1.5H2O )4 = 4NH3(g) + 5O2(g) = 4NO(g) +6H2O 1 mol of NH3 = 14 grams + 3*(1g)= 17 grams of NH3 34/17 = 2 mol of NH3 given 1 mol of O2 = 32 grams 32/32 = 1 mol of O2 given Oxygen is the limiting reagent. How many moles of NH3 can you react with 1 mol of O2 0.8 NH3 + 1O2 = 0.8NO + 6/5H2O - if you divide everything by 5 to get the ratio. NO produced? 0.8 mols of NO 1 molecule of NO = 30 grams so, 0.8*30 = 24 grams NO

What is the difference between the empirical, molecular and structural formula?

Empirical Formula - A formula that gives the simplest whole-number ratio of atoms in a compound. Molecular Formula - a formula giving the number of atoms of each of the elements present in one molecule of a specific compound. Structural Formula - a graphic representation of the molecular structure, showing how the atoms are possibly arranged in the real three-dimensional space.

What is the formula to calculate how many equivalents of a compound you have when you have found the mass of the compound in grams?

Equivalents = Mass of compound (g) / Gram equivalent weight (g)

True/False? Coefficients can represent moles, molecules, atoms and mass.

False, They never represent mass. ONLY represent # of: moles, molecules and atoms

True/False? Ionic compounds can have empirical and molecular formulas?

False, Ionic compounds only contain empirical formulas.

P4(s) + Cl2(g) = PCl3(l) In the given equation above how many grams of Cl2 are required and How many grams of PCl3 are produced when given 1.45g of P4(s)?

First, Balance: P4(s) + 6Cl2(g) = 4PCl3(l) Now, how many moles of P4(s) are there? 31 amu = 1 mole = 34 grams 31*4(atoms of P) = 1 mole of P4(s) = 124g Then, if given 1.45g P4, how many moles do you have? 1.45g P4*(1 mol P4 / 124 g) = 0.0117 mol P4 now we can see for every mole of P4 we have 6 moles of Cl2. 0.0117 mol P4 (6 mol Cl2 / 1 mol P4) = 0.07 mol of Cl2(g) required. 0.07 mol Cl2(g) x (70.906g Cl2 / 1 mol Cl2) = 4.96 g Cl2(g) are required. Next: easy way: mass is conserved so mass of reactant = mass of product. = 6.41 g PCl3 are produced

What kind of reaction occurs whenever a compound undergoes a reaction without changing its molecular formula?

It is a physical reaction. Ex. melting, freezing, evaporation, condensation, etc.

What is the formula to convert normality to molarity of a given solute?

Molarity = Normality / n n = protons, hydroxide ions, hydrogen ions, electrons, or ions produced or consumed by the solute.

What is the measurement of normality of a compounds concentration in a solution?

Normality is the measure of concentration, in units of equivalents/L. - 1 N of a solution of acid contains 1 mol/L of the hydrogen ion.

What is percent composition and how do you calculate it?

Percent composition is the percent of a specific compound that is made up of a given element. Percent composition = mass of element in formula / mass of compound* 100%

What is stoichiometry?

The calculation of quantitative (measurable) relationships of the reactants and products in a balanced chemical reaction (chemicals). It can be used to calculate quantities such as the amount of products that can be produced with the given reactants and percent yield.