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Types of Chemical Reactions

by Steve M. Hall

Ms. A. StewartSCH4C

March 5th, 2013

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Introduction:It is not easy to classify all chemical reactions precisely. Nevertheless, most reactions can be classified into one of four major categories.

SynthesisAddition reactions or direct combinations are reactions in which atoms and molecules join together directly to produce larger molecules. An example of an addition reaction is the combustion of sulfur to form sulfur dioxide:

S + O2 → SO2

Synthesis is a very common reaction in organic chemistry. A significant discovery involving synthesis reactions, is one by Friedrich Wöhler, a German scientist who discovered the Wöhler synthesis. This was the first an organic compound was produced from inorganic reactants.

Decomposition Decomposition reactions are just the opposite of addition reactions. An example is the decomposition of carbonic acid:

H2CO3 → H2O + CO2

There are three broad types of decomposition reactions: thermal, electrolytic and catalytic. Thermal decomposition is a chemical decomposition caused by heat. An example of this is calcium carbonate (chalk) decomposes into calcium oxide and carbon dioxide when heated. Electrolytic decomposition involves a current being passed through a substance. For example, electrolysis of water is the decomposition of H2O into oxygen and hydrogen gas, by means of an electric current being sent through the water. Catalytic decomposition involves a catalyst speeding up a reaction that would happen over time.

Single DisplacementDisplacement or substitution reactions involve a change of partners. An example of a displacement reaction is the liberation of bromine from calcium bromide by the action of chlorine:

Cl2 + CaBr2 → CaCl2 + Br2

Double DisplacementDouble displacement or metathetic reactions involve a joint exchange of partners, as in the precipitation of silver chloride when solutions of silver nitrate and sodium chloride are mixed:

AgNO3 + NaCl → AgCl + NaNO3

In this experiment, you will study five different chemical reactions. You will identify some of the products and then classify each reaction as one of the four types.

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Purpose:To study four different types of chemical reactions

Apparatus:• crucible tongs• 150 mm test tubes (5)• medicine dropper• 10 mL graduated cylinder• test tube holder

Materials:• wood splints• 0.5 mol/L sodium sulphate• 0.5 mol/L barium chloride• mossy zinc• 3 mol/L hydrochloric acid• manganese dioxide• iron nail• 0.3 mol/L copper (II) sulphate• copper wire• 6% hydrogen peroxide

Procedure:Station B: Place 5 mL of sodium sulphate solution in a test tube. Add a medicine dropper full

of barium chloride solution.

Station C: Using crucible tongs, hold a 5 cm piece of copper wire in a burner flame. Remove the wire and examine it.

Station D: Place a small piece of mossy zinc in a test tube. Add 5 mL of dilute hydrochloric acid.

Station E: Place 3 mL of hydrogen peroxide in a test tube. Add a pinch of manganese dioxide. Insert a glowing splint into the mouth of the test tube. *Water is one product of this reaction.

Station F: Place a clean iron nail in a test tube and cover it with a solution of copper (II) sulphate. After several minutes, remove the nail and examine it.

Hypothesis:Station B: I think this will be a double displacement reaction.

Station C: I think this will be a synthesis reaction.

Station D: I think this will be a decomposition reaction.

Station E: I think this will be a single displacement reaction.

Station F: I think this will be a single displacement reaction.

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Observations & Data:

Station Reactants Appearance of Reactants Prior to Reaction

(Qualitative Observations)

Observations During Reaction

Station B: BaCl2 (aq) + Na2SO4 (aq)

(barium chloride + sodium sulphate)

They are both clear liquids, like water

Turns opaque and milky white.

Station C: Cu2+ + O2 (copper wire + oxygen)

Shiny, bronze colored wire Green flame being omitted, copper gaining black soot

Station D: Mossy zinc and hydrochloric acid

Moss is small, gray and chalk-like, very brittle. Hcl (aq) is clear, odourless, colourless, like water.

Bubbling, hydrogen evaporating as gas (H2), fizzing, gas produced

Station E: Hydrogen peroxide, manganese dioxide (MnO2)

Manganese dioxide: black powder, odourless. Hydrogen peroxide: colourless, transparent liquid.

Oxygen gas produced, water produced, heat omitted.

Station F: Copper (II) sulphate and iron nail (CuSO4 (aq) + Fe)

Copper sulphate aqueous: light blue, transparent liquid. Nail: silver, malleable.

Nail begins to rust.

Results & Discussion:1. [Station B] What do you observe?

As soon as the barium chloride touches the sodium sulphate, a double displacement reaction occurs. The barium trades places with sodium, creating sodium chloride (salt) and barium sulphate. This creates a white opaque liquid, very different from the original clear liquids. (see Figure 1) No precipitate is created, nor is a gas. No heat is omitted.

2. [Station B] If one of the products is sodium chloride (which is soluble in water), what is the other product?

The other product is barium sulphate, which is actually a product available behind the counter in drugstores and pharmacies, used as a laxative during a colonoscopy and CT scan preparation. (see Figure 2)

3. [Station C] What do you observe?After the copper wire has been in the flame for a few seconds, the flame becomes a green colour. (see Figure 3) The copper wire becomes black and sooty.

4. [Station C] With what did the copper combine? The copper synthesized with the oxygen in the flame, creating copper (II) oxide, which

is what caused the green flame.

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(Results & Discussion continued)5. [Station D] What do you observe?

When the mossy zinc is inserted into the hydrochloric acid, bubbling begins, which is the hydrogen in from the hydrochloric acid evaporating. (see Figure 4&5) What is left in the tube is zinc chloride, an aqueous solution.

6. [Station E] What do you observe?When the manganese dioxide is inserted into the hydrogen peroxide, a gas is produced. The hydrogen peroxide turns black from the manganese dioxide. Heat is omitted. Manganese dioxide is the catalyst in this catalytic decomposition reaction. (see Figure 6)

7. [Station E] (after inserting a glowing splint) What do you observe?After inserting a glowing splint, the flame gets bigger, showing us a gas has been formed. This gas is oxygen. What is left is water.

8. [Station E] If water is one of the products in this reaction, what is the other product?The other product is oxygen gas.

9. [Station F] Do you observe any change in the appearance of the nail?Yes, there is a change in appearance of the nail.

10. [Station F] If so, what is the change?The nail begins to rust.

11. [Station F] Do you observe any change in the appearance of the copper (II) sulphate solution?Yes, I do observe a change in the appearance of the solution.

12. [Station F] If so, what is the change?The colour becomes a lighter shade of blue.

Conclusions:1. What word equations describe the chemical reactions taking place in parts B-F

Station B: Barium chloride + Sodium sulphate → Sodium chloride + Barium sulphate

Station C: Copper (II) + Oxygen gas → Copper (II) oxide

Station D: Zinc + Hydrochloric acid → Hydrogen gas + Zinc chloride

Station E: Hydrogen peroxide + Manganese dioxide → Dihydrogen monoxide (water) + Oxygen gas

Station F: Copper sulphate + Iron → Copper + Iron sulphate

2. What type of chemical reaction is illustrated in each part of this experimentStation B: Double displacement

Station C: Synthesis

Station D: Single displacement

Station E: Decomposition (catalytic)

Station F: Single displacement

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(Conclusions continued)3. What is the balanced chemical equation for each reaction taking place in parts B-F

Station B: Na2SO4 (aq) + BaCl2 (aq) → BaSO4 + 2NaCl (aq)

Station C: 2Cu + O2 → 2CuO

Station D: Zn (s) + 2HCl (aq) → ZnCl2 (aq) + H2 (g)

Station E: 2H2O2 (aq) → O2 + 2H2O (l)

Station F: Fe + CuSO4 → FeSO4 + Cu

Appendices:

Figure 1 Figure 2

Figure 3

Figure 4

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Figure 5Figure 6

Figure 7

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http://www.cliffsnotes.com/study_guide/topicArticleId-276493,articleId-276379.htm

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Guch. (n.d.). The six types of chemical reactions. Retrieved March 26, 2013, from Mr Guch's Home Page website: http://misterguch.brinkster.net/6typesofchemicalrxn.html

Haberer, S., & DiGiuseppe, M. (2011). Nelson chemistry 11: University preparation. Toronto, Ont.: Thomson/Nelson.

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Hein, M., & Arena, S. (2004). Foundations of college chemistry (11th ed.). Hoboken, NJ: Wiley.

Schaefer, S., & Sherman, J. (Writers), & Suto, D. (Director). (1994, March 11). Chemical reactions [Television episode]. In E. Brock, E. Gottlieb, & J. McKenna (Producer), Disney's Bill Nye the science guy. Disney Broadcasting Company.

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