BSC 2093 Fall 2010

Name:______

Review Concepts in Chemistry

Periodic Table of Elements

1. Chemical Quantities

A. The Mole:

The mole is an SI unit of measurement for the amount of a substance

The mole (mol) is a defined number of particles of a substance:

- A pair = ____ of anything

- A dozen = ____ of anything

- A mole = Avogadro’s Number of anything

- Avogadro’s Number = 6.022 x 1023 particles

1 mole of a substance = 6.022 x 1023 particles (atoms, molecules) of the substance

Calculating the number of moles of a substance:

  1. How many dozens of doughnuts are 246 doughnuts?
  1. How many doughnuts is 13 dozen doughnuts?
  1. How many moles of magnesium (Mg) is 1.25 x 1023 atoms of Mg?
  1. How many molecules of propane (C3H8) are in 2.12 moles of propane?

B. Molar Mass:

The mass of elements and molecules is measured in grams per mole (g/m)

The molar masses of the elements are found on the Periodic Table as the atomic mass number

The molar masses of molecules is calculated by adding the molar masses of all of the elements in the molecule

Calculating the molar mass of a substance:

  1. What is the molar mass of elemental oxygen (O)?
  1. What is the molar mass of molecular oxygen (O2)?
  1. What is the molar mass of Glucose?

C. Mole-Mass Conversions

The molar mass of substances can be used as a conversion factor for the mass of a substance (g) and the number of moles of a substance

Converting moles of a substance to mass (g):

  1. How many grams are in 9.45 mol of dinitrogen trioxide (N2O3)?
  1. How many moles of propane C3H8 are in 100 g propane?
  1. Calculate the mass, in grams, of 3.32 mol Potassium (K)

Converting the mass of a substance to moles:

  1. Find the number of moles in 92.2 g of iron oxide (Fe2O3)?
  1. 75.0 g N2 is how many moles?
  1. 847 g (NH4)2CO3 is how many moles?

D. Stoichiometry

Chemical equations that are balanced describe the ratio of reactants to products

The ratio of products and reactants can be used to: a. predict the amount reactants required to carry out a chemical reaction, or b. the amount product that will be produced by the chemical reaction

Balance the chemical equation and use the information to solve:

H2S + O2  SO2 + H2O

  1. Calculate the number of moles of oxygen required to produce 6 moles of sulfate (SO2)
  1. Calculate the number of moles of H2O that can be produced from 4 moles of hydrogen sulfide (H2S)
  1. How many grams of SO2 are produced from 150 g H2S
  1. How many grams of H2O are produced from 35 g H2S

E. Review

Balance the following chemical equations:

  1. N2 + H2  NH3
  1. Based on your balanced equation from the previous question, determine the amount in grams of N2 required to produce 68 grams of NH3.
  1. C2H2 + O2  CO2 + H2O
  1. Based on your balanced equation from the previous question, determine the amount in grams of C2H2 required to produce 15 grams of CO2.
  1. C3H7OH + O2  CO2 + H2O
  1. Based on your balanced equation from the previous question, determine the amount in grams of C3H7OH required to produce 3 moles of CO2.
  1. Fe2O3 + CO  Fe + CO2

2. Solutions

A. Properties of Solutions

A solution is a homogenous mixture of different substances

Every solution is composed of two parts:

  1. The Solvent – the more abundant substance, usually water (an aqueous solution)
  2. The Solute – the less abundant substance (particles) dissolved in the solvent

B. Concentrations of Solutions

The concentration of a solution is a measure of the amount solute dissolved in a given quantity of solvent

A concentrated solution has a high concentration of solute dissolved in the solvent

A dilute solution has a low concentration of solute dissolved in the solvent

C. Molar Concentrations:

Molar concentrations describe the number of moles of solute dissolved in a given quantity of solvent

Molarity (M): Moles of solute per liters of solution (moles per liter, mol/L)

Molarity (M) = mole of solute (mol)

liters of solution (L)

Molarity is constant throughout the solution

Molarity does not depend on the amount of solution

Calculations with molarity:

  1. What happens to the molarity of a solution if more solvent is added?
  1. A saline solution contains 0.90 g NaCl dissolved in 100 mL of solution. What is the molarity of the solution?
  1. How many moles of solute are present in 1.5 L of 0.24 M Na2SO4?
  1. A solution has a volume of 2.0 L and contains 36.0 g of glucose. What is the molarity of the solution?
  1. A solution has a volume of 250 mL and contains 0.70 mol NaCl. What is the molarity of the solution?
  1. How many moles of ammonium nitrate are in 335 mL of 0.425 M NH4NO3?
  1. How many moles of solute are in 250 mL of 2.0 M CaCl2?
  1. How many grams of CaCl2 is this?

D. Making Dilutions

It is often necessary to dilute a given stock solution to a different concentration

A solution can be made less concentrated by diluting it with more solvent

Making a dilution reduces the number of moles per unit volume (L), but the total number of moles of solute in solution is not changed

Moles of solute before dilution = moles of solute after dilution

Molarity (mol) = Moles of solute (mol)

Liters of solution (L)

Moles of solute = molarity (M) x liters of solution (L)

Moles of solute = Mi x Vi = Mf x Vf

Where Mi and Vi are the initial molarity and volume before the dilution and Mf and Vf are the final molarity and volume after the dilution.

Preparing dilutions:

  1. How many milliliters of a stock solution of 2.00M MgSO4 are needed to prepare 100.0 mL of 0.400M MgSO4?
  1. How many milliliters of a stock solution of 4.00M KI would you need to prepare 250.0 mL of 0.760M KI?
  1. You need to prepare 250 mL of 0.2M NaCl, but the only supply of sodium chloride you have is a solution of 1.0M NaCl. How do you prepare the required solution?