Experiment 2 a Types of chemical reaction and tests for f or gases
Objectives: To use Flame Tests to identify compounds of Group 1 and Group 2 by observing the colours of the flame produced.
Materials: Looped wire for flame test, Dilute Hydrochloric acid, Watch glass, Bunsen burner, Spatula, Sodium chloride, Potassium chloride, Barium chloride, Calcium chloride
Methods: 1. Transfer half a spatula spatula of the a solid solid provided (A, B, C or D) in a watch glass. 2. Add a few drops of diluted HCl solution solution on to the solid, to make a paste.
3. Dip a clean piece of platinum platinum or tungsten wire into the acidic paste. 4. Hold the wire at the edge of a blue Bunsen Bunsen flame flame and note the colour of the the flame
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Results: Test
Observation
a) Unknown A
Yellow
orange
flame
The cation present is……… is Sodium ( + ) ion is present.
produced. b) Unknown B
Lilac
(purple
flame)
is Potassium ( +) ion is present.
produced. c) Unknown C
Apple green flame is produced. Barium ( 2 ) ion is present.
d) Unknown D
Brick-red flame is produced.
Calcium ( 2+ ) ion is present.
Discussion: 1.
Explain how the Flame Tests could be used to identify the compounds. Metals are composed of individual atoms, which contain a nucleus consisting of protons and neutrons as the outer shells consists of electrons floating freely around the nucleus. Metal atoms usually exist in the form of ions, which are cations or an atom with a charge. The electrons of metal ions circle the nucleus in orbitals. The energy level of these electrons increases as the orbitals get further away from the nucleus. Electrons need to absorb energy to move to a higher energy orbital. During the flame tests, the metal ions are exposed to heat energy from the flame of the Bunsen burner. The electrons absorb the thermal energy and move from lower to higher energy level. As the electrons get even more excited, they will be released to the surrounding in the form of light and heat energy, producing different colours of flame depending on the wavelength of light. Once the electrons are not exposed to thermal energy, they will eventually fall back to their ground energy level. All metals will produce different wavelengths of light during the flame test due to different electron configurations. Different wavelengths have different colours. Light with longer wavelengths appears red, whereas light with shorter wavelengths appears purple. Thus, each metal will produce a characteristic colour of light, which makes the flame change colours. 2
2.
Give a use for these Flame Tests. Geologists use the flame tests to identify the presence of metals. Forensic scientists can use flame tests at crime scenes for quick analysis of elements present. Miners use the test for analysis of samples, particularly when prospecting. Flame tests also provide a good teaching tool for chemistry students learning about emission spectra.
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Experiment 2 b
Objectives: To investigate the; (a) Redox reactions between a metal and dilute acid (b) Redox reactions of metal-metal ion displacement reaction (c) Redox reactions of Halogen displacement reaction
Materials: Test Tubes, 2 Stripes of each of the following metals; copper, lead, magnesium and zinc, 2.0 M hydrochloric acid (10ml) in labelled test tube,1 M solutions of the following salt solutions: Copper (II) nitrate, Lead (II) nitrate, Magnesium nitrate and Zinc nitrate, Potassium bromide, Potassium chloride and Potassium iodide, Chlorine water, Bromine solution and Iodine solution, Hexane solution, Test tubes, Bunsen burner and Sand paper.
Methods: A. Metal – Acid reaction 1. Arrange four test tubes on a test tube stand. Label the test tubes accordingly. 2. Add 2.0 ml dilute HCl acid into each test tube. 3. Place a piece of copper metal into the first test tube, a lead metal into the second test tube, zinc strip into the third test tube and a magnesium ribbon into the fourth tube. 4. Compare the reactivity of the metals with the acid and record your observations.
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B. Metal –Metal ion Reaction 1. Place a zinc strip into 3 different test tubes. 2. Place a zinc strip into 3 different test tubes. 3. Add 1 M Magnesium nitrate solution into the first test tube, 1 M Lead (II) nitrate solution into the second test tube and 1 M Copper (II) nitrate solution into the third test tube. 4. Record all your observations. 5. Repeat steps (1) and (2) for magnesium, lead and copper metals.
C. Halogen displacement Reaction 1. To 2.0 ml KBr solution, in a test tube, add about 2.0 ml chlorine water; stir. 2. Observe any change. 3. Add about 1.0 ml hexane ( 6 14 ) to the same test tube and stir. Allow the hexane layer to settle down. Note the colour of this layer. 4. Record the colour of the hexane layer. 5. Repeat steps (1) → (4), for the following reactions: 2 ,
2 ,
2 ,
2 ,
2
Results: A: Metal – Acid reaction Metal used
Reaction with dilute HCl (aq)
Copper
No reaction occurred.
Lead
Very slow reaction. A few bubbles of colourless gas are produced.
Zinc
Moderately fast reaction. Some bubbles of colourless gas are produced.
Magnesium
Very fast reaction. Bubbles of colourless gas are rapidly produced. 5
B. Metal – Metal ion Reaction:
Solution
Magnesium
Zinc
Lead (II)
Copper (II)
nitrate (aq)
nitrate (aq)
nitrate (aq)
nitrate (aq)
Metal
Mg
X
Grey solid is Shiny
grey Black
deposited. The solid solution
solution
reaction
occurred.
X
The
Shiny
grey Black
solid
deposited. The colour
colourless.
solution
reaction No
occurred.
Cu
reaction
is
solid
of
is solution
X
The occurred. The
decolourised Black
solid
colourless.
remains
solution
colourless.
decolourised.
occurred.
is
deposited. Blue colour
reaction No
the is
solution remains solution
No
is
is deposited. Blue
solution remains
No
the
decolourised.
colourless. Pb
of
is solution
colourless. No
is
is deposited. Blue
is deposited. The colour
colourless.
Zn
solid
reaction No
reaction
of
the is
X
The occurred. The occurred. The
solution remains solution
solution
colourless.
remains
remains
colourless.
colourless.
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C. Halogen displacement Reaction: Reaction
Observation before adding hexane
Colour of the hexane layer
2 +
Yellow brown solution formed
Brownish yellow
2 +
Brown solution formed
Dark purple
2 +
No reaction
Brownish yellow
2 +
Colour changes from yellow-orange Dark purple to brown
2 +
No reaction
Dark purple
2 +
No reaction
Dark purple
Discussion:
1. Write balanced ionic equation for the reactions that took place in the:
a) Metal – Acid Reaction i.
2H++ Cu → H2 + Cu2+
ii.
2H+ + Pb → H2 + Pb2+
iii. 2H+ + Zn → H2 + Zn2+ iv. 2H+ + Mg → H2 + Mg2+
b) Metal – Metal ion Reaction Magnesium metal: i.
Mg + Zn2+ → Mg2++ Zn
ii. Mg + Pb2+ → Mg2+ + Pb iii. Mg + Cu2+ → Mg2++ Cu
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Zinc metal: i.
Zn + Pb2+ →Zn2+ + Pb
ii. Zn + Cu2+ →Zn2+ + Cu
Lead metal: Pb: Pb + Cu2+ →Pb2+ + Cu
c) Halogen Displacement Reaction Chlorine water: Cl2 + 2Br - → 2Cl - + Br 2 Cl2 + 2I- → 2Cl - + I2
Bromine water: Br 2 : Br 2 + 2I- → 2Br - + I2
2. Which metal did not react with HCl (aq)? Give an explanation for this. Copper metal did not react with hydrochloric acid because it has higher reduction potential than hydrogen. Copper has a lower position than hydrogen in the reactivity series of metals, thus it is less reactive than hydrogen. Therefore, copper cannot displace hydrogen from the acid.
3. Which metal is the most electropositive? Magnesium.
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References:
Internet document
Reactions
of
Metals.
S-cool.co.uk
S-cool,
the revision.
http://www.s-cool.co.uk/gcse/chemistry/metals-the-reactivityseries/revise-it/reactions-of-metals. ThoughtCo.
How
To
Do
A
Flame
Test.
ThoughtCo.
https://www.thoughtco.com/perform-and-interpret-flame-tests603740 Reference. What are Some Uses For Flame Test. Reference. https://www.reference.com/science/uses-flame-testsf4910d776a6ffe42 Amanda Robb. Using Flame Tests to Identify Metal Ions. Study. http://study.com/academy/lesson/using-flame-tests-to-identifymetal-ions.html
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