Chemistry

Unit: Chemical Reactions

Name: ______Date: ______MOD: ______

Student Sheet: Identification of Anions and Cations in Solution

PART 1: Flame Tests for Cations

DATA TABLE I

Table of Flame Tests

Ion / Flame Color
sodium, Na+ / ______
sodium, Na+ (cobalt glass) / ______
potassium, K+ / ______
potassium, K+ (cobalt glass) / ______
calcium, Ca2+ / ______
barium, Ba2+ / ______
strontium, Sr2+ / ______
lithium, Li+ / ______
copper(II), Cu2+ / ______

QUESTIONS

  1. List several elements that could be identified based on their characteristic flame color. ______

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  1. Explain why some elements are difficult to identify by flame color.

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  1. Which element produces the most intense color? ______

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  1. Would flame tests be useful for detecting specific cations present in a mixture of metal ions? Why? ______

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  1. What is the purpose of using cobalt glass in the identification of sodium and potassium? ______

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  1. Problem Solve: You are enjoying a July 4th fireworks display when one of the rockets explodes prematurely. The color of the explosive mixture is yellow, green, and red-orange. Which three metals were most likely present in the rocket? Support your answer with evidence from the flame tests you performed. ______

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PART 2: Qualitative Tests for Anions

Qualitative Tests for Anions
Known Anion / Indicator / Observations
a)4 drops 5% NaCl / 2 drops 0.2 M AgNO3 / ______
b)4 drops 5% NaNO3 / 2 drops 0.2 M AgNO3 / ______
c)4 drops 5% Na2S / 2 drops 0.2 M AgNO3 / ______
d)4 drops 5% Na2SO4 / 2 drops 0.2 M AgNO3 / ______
e)4 drops 5% Na2SO4 / 2 drops 0.2 M Pb(NO3)2 / ______
f)4 drops 5% NaI / 2 drops 0.2 M Pb(NO3)2 / ______
g)4 drops 0.6 M NaHCO3 / 2 drops 0.2 M Pb(NO3)2 / ______
h)4 drops 0.6 M NaHCO3 / 2 drops 3.0 M HCl / ______

QUESTIONS

  1. Underline the anion being tested in 2a-h.
  1. Explain why it is necessary to test sodium sulfate with lead nitrate.

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  1. Justify your observation in 2b. Explain why you did not observe a similar result when AgNO3 was addedto NaCl or Na2S.

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  1. Write a balanced equation for each chemical reaction that gave a positive qualitative test.
  • NaCl + AgNO3 AgCl + ______
  • Na2S + 2AgNO3 Ag2S + ______
  • Na2SO4 + ______) PbSO4 + 2NaNO3
  • 2NaI + ______ PbI2 + 2NaNO3
  • 2NaHCO3 + Pb(NO3)2  Pb(HCO3)2 + ______
  • NaHCO3 + ______ NaCl + CO2 + H2O (also accept NaCl + H2CO3 as products of the reaction)

Part III: Unknown

Unknown Letter: ______

Identify your unknown: ______

Give a brief description about the methods used to determine your unknown.

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EXTENSION

THINK and then WRITE: Use your knowledge about valence electrons, atomic radii, ionization energy, orbital energies, the process of emitting light, and additional reference material as needed to explain why the emitted light in the flame test for sodium is yellow while the light emitted for strontium is bright red-orange. For full credit you must give a thorough explanation in a well-written paragraph.

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