CHM1020 Week 5

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South College *

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1020

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Chemistry

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Jan 9, 2024

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Name(s): ____Casey Zufall ______________ CHM 1020 W5 Week 5 Assignment Objective In today’s lab, we will demonstrate a few different types of chemical reactions and be able to observe whether a chemical reaction has taken place. We will also learn how to use chemical equations to describe chemical reactions. Background/Theory The Periodic Table shows over 100 elements. The chemical literature describes millions of compounds that are known—some isolated from natural sources, some synthesized by laboratory workers. The combination of chemicals, in the natural environment or the laboratory setting, involves chemical reactions. The change in the way that matter is composed is a chemical reaction , a process wherein reactants (or starting materials) are converted into products. The new products often have properties and characteristics that are entirely different from those of the starting materials. Four ways in which chemical reactions may be classified are combination, decomposition, single replacement (substitution), and double replacement (metathesis). Two elements reacting to form a compound is a combination reaction . This process may be described by the general formula: A + B ⟶ AB The rusting of iron or the combination of iron and sulfur are good examples. 4Fe(s) + 3O 2 (g) ⟶ 2Fe 2 O 3 (s) (rust) Fe(s) + S(s) ⟶ FeS(s) Two compounds reacting together as in the example below also is a combination reaction. CaO(s) + CO 2 (g) ⟶ CaCO 3 (s) A compound which breaks down into elements or simpler components typifies the decomposition reaction . This reaction has the general formula: AB ⟶ A + B Some examples of this type of reaction are the electrolysis of water into hydrogen and oxygen: 2H 2 O(l) ⟶ 2H 2 (g) + O 2 (g) and the decomposition of potassium iodate into potassium iodide and oxygen: 2KIO 3 (s) ⟶ 2KI(s) + 3O 2 (g) The replacement of one component in a compound by another describes the single replacement (or substitution ) reaction. This reaction has the general formula: AB + C ⟶ CB + A Page 1 of 7

Name(s): ____Casey Zufall ______________ CHM 1020 W5 Processes which involve oxidation (the loss of electrons or the gain of relative positive charge) and reduction (the gain of electrons or the loss of relative positive charge) are typical of these reactions. Use of Table 1, the activity series of common metals, enables chemists to predict which oxidation-reduction reactions are possible. A more active metal, one higher in the table, is able to displace a less active metal, one listed lower in the table, from its aqueous salt. Thus aluminum metal displaces copper metal from an aqueous solution of copper(II) chloride; but copper metal will not displace aluminum from an aqueous solution of aluminum(III) chloride. 2Al(s) + 3CuCl 2 (aq) ⟶ 3Cu(s) + 2AlCl 3 (aq) Cu(s) + AlCl 3 (aq) ⟶ No Reaction ( Note that Al is oxidized to Al 3+ and Cu 2+ is reduced to Cu. ) Hydrogen may be displaced from water by a very active metal. Alkali metals are particularly reactive with water, and the reaction of sodium with water often is exothermic enough to ignite the hydrogen gas released. 2Na(s) + 2HOH(l) ⟶ 2NaOH(aq) + H 2 (g) + heat (Note that Na is oxidized to Na + and H + is reduced to H 2 .) Active metals, those above hydrogen in the series, are capable of displacing hydrogen from aqueous mineral acids such as HCl or H 2 SO 4 ; however, metals below hydrogen will not replace hydrogen. Thus zinc reacts with aqueous solutions of HCl and H 2 SO 4 to release hydrogen gas, but copper will not. Zn(s) + 2HCl(aq) ⟶ ZnCl 2 (aq) + H 2 (g) Cu(s) + H 2 SO 4 (aq) ⟶ No reaction Two compounds reacting with each other to form two different compounds describes double replacement reactions. This process has the general formula: AB + CD ⟶ AD + CB There are two replacements in the sense that A replaces C in CD and C replaces A in AB. This type of reaction generally involves ions which form in solution either from the dissociation of ionic compounds or the ionization of molecular compounds. The reaction of an aqueous solution of silver nitrate with an aqueous solution of sodium chloride is a good example. The products are sodium nitrate and silver chloride. We know a reaction has taken place since the insoluble precipitate silver chloride forms and separates from solution. AgNO 3 (aq) + NaCl(aq) ⟶ NaNO 3 (aq) + AgCl(s) (White precipitate) In general, a double replacement results if one combination of ions leads to a precipitate, a gas or an un- ionized or very slightly ionized species such as water. In all of these reaction classes, it is very often possible to use your physical senses to observe whether a chemical reaction has occurred. The qualitative criteria may involve the formation of a gaseous product, the formation of a precipitate, a change in color, or a transfer of energy. In the next section, you will practice identifying which of the four classes or classification of chemical reactions mentioned above does each chemical reaction represent. Note, in addition to combination, decomposition, single replacement and double replacement reactions, we also have combustion reactions, which you will explore in later assignments. For now, each reaction listed will fall into one of the four categories described here. Page 2 of 7

Name(s): ____Casey Zufall ______________ CHM 1020 W5 Practice determining reaction classification For each of the reactions below, classify as a combination, decomposition, single replacement, or double replacement. 1. Ca(s) + Cl 2 (g) ⟶ CaCl 2 (s) Combination 2. 2Cu(s) + O 2 (g) ⟶ 2CuO(s) Combination 3. Ca(NO 3 ) 2 (aq) + H 2 SO 4 (aq) ⟶ 2HNO 3 (aq) + CaSO 4 (s) Double displacement 4. NH 3 (aq) + HCl(aq) ⟶ NH 4 Cl(aq) Combination 5. Hg(NO 3 ) 2 (aq) + 2NaI(aq) ⟶ HgI 2 (s) + 2NaNO 3 (aq) Double displacement 6. AgNO 3 (aq) + NaCl(aq) ⟶ AgCl(s) + NaNO 3 (aq) Double displacement 7. Zn(s) + H 2 SO 4 (aq) ⟶ ZnSO 4 (aq) + H 2 (g) Single displacement 8. H 2 CO 3 (aq) ⟶ CO 2 (g) + H 2 O(l) Decomposition 9. 2H 2 O(l) ⟶ 2H 2 (g) + 2O 2 (g) Decomposition 10. 2Li(s) + 2H 2 O(l) ⟶ 2LiOH(aq) + H 2 (g) Combination Page 3 of 7

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