Exp 12: Flame Tests

Your job is to prepare solutions of different elements. Burn a droplet of each solution in a bunsen burner. Take note of differences in color, persistence, and secondary properties of the flame of each element.

First explore how concentration effects the flame. For three elements, dilute their solutions into four different concentrations. Report which gave the best persistent (3-5 second) flame.

Next explore how the flames differ as you move across the fourth period and down the alkali metals. Look for patterns, trends, and exceptions in colors related to the atoms position on the periodic table. Explain your observations based on the relative energy of available orbitals for each element.

Finally, you will be given an unknown sample and asked to identify it based on the data you have collected.

Exp 12: Flame Tests

General Procedures for Each Flame Test

Exp 12: Flame TestsPart A: Concentration Effect

0.20 M

0.60 M

1.2 M

1.8 M

‣ Stock solutions are solutions of known concentration.

‣ Most solutions are made by diluting a stock solution to a new molarity.

‣ Dilution just means adding more solvent.

‣ Dilution never changes the number of mols dissolved in the solution. — just the volume of the solution around them.

‣ Molarity and volume change with dilution, but because the mols don’t change… — the ratio of volume to molarity is constant.

‣ What volume must you dilute 25 mL of 8.0 M Ca(NO3)2 to make a 2.0 M solution?

‣ How many mL of 6.0 M HCl (aq) do you need to make 200. mL of 2.0 M HCl (aq)?

only when diluting!

moles before = moles after

Important:

— Don’t confuse stoichiometry with dilution problems!

Exp 12: Flame Tests

Exp 12: Flame TestsPart A: Prepare your Solutions

0.20 M

0.60 M

1.2 M

1.8 M

Exp 12: Flame Tests

Part B: Trends, Patterns, and Exceptions in Fourth Period

Exp 12: Flame Tests

Part C: Trends, Patterns, and Exceptions in First Group

Exp 12: Flame Tests

Part D: Unknown

Questions?