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.
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)+3O2(g) ?2Fe2O3(s)(rust)
Fe(s)+S(s) ?FeS(s)
Two compounds reacting together as in the example below also is a combination reaction.
CaO(s) +CO2(g) ?CaCO3(s)
A compound which breaks down into elements or simpler components typifies thedecomposition 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:
2H2O(l) ?2H2(g) +O2(g)
andthedecompositionofpotassiumiodateintopotassiumiodideandoxygen:
2KIO3(s)?2KI(s)+3O2(g)
The replacement of one component in a compound by another describes the singlereplacement(or substitution) reaction. This reaction has the general formula:
AB + C ?CB + A
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) +3CuCl2(aq) ?3Cu(s) +2AlCl3(aq)
Cu(s) + AlCl3(aq) ?No Reaction
(Note that Al is oxidized to Al3+ and Cu2+ 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) + H2(g) + heat
(Note that Na is oxidized to Na+ and H+ is reduced to H2.)
Active metals, those above hydrogen in the series, are capable of displacing hydrogen from aqueous mineral acids such as HCl or H2SO4; however, metals below hydrogen will not replace hydrogen. Thus zinc reacts with aqueous solutions of HCl and H2SO4 to release hydrogen gas, but copper will not.
Zn(s)+2HCl(aq)?ZnCl2(aq)+H2(g) Cu(s)+H2SO4(aq)?Noreaction
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.
AgNO3(aq) +NaCl(aq) ?NaNO3(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.
Practice determining reaction classification
For each of the reactions below, classify as a combination, decomposition, single replacement, or double replacement.
Ca(s)+Cl2(g)?CaCl2(s)
2Cu(s) + O2(g)?2CuO(s)
Ca(NO3)2(aq)+H2SO4(aq)?2HNO3(aq)+CaSO4(s)
NH3(aq)+HCl(aq) ?NH4Cl(aq)
Hg(NO3)2(aq)+2NaI(aq)?HgI2(s)+2NaNO3(aq)
AgNO3(aq)+NaCl(aq)?AgCl(s)+NaNO3(aq)
Zn(s)+H2SO4(aq)?ZnSO4(aq)+H2(g)
H2CO3(aq)?CO2(g)+H2O(l)
2H2O(l)?2H2(g)+2O2(g)
2Li(s)+2H2O(l)?2LiOH(aq)+H2(g)
Procedure for Experiments
Combination/Synthesis Reactions
Watch the following Video: https://www.youtube.com/watch?v=w2ydd9rJHws
For the reaction of magnesium and atmospheric (diatomic) oxygen write out the balanced chemical equation:
Next describe what magnesium metal looks like, and what the product identified above looks like. For example, was the magnesium reactant shiny or dull, was it malleable or brittle?
Decomposition Reaction
Watch the following video: https://www.youtube.com/watch?v=_Y1alDuXm6A
Write out the balanced chemical equation for the thermal decomposition of Mercury oxide:
What did the Mercury (II) oxide reactant look like, and what did the products of the decomposition reaction look like?
How do we know the gas released was oxygen?
Single Displacement Reaction
Watch the following video: https://www.youtube.com/watch?v=k8UtR7akNec
Write out the balanced chemical equation for single replacement reaction of silver nitrate and copper:
Describe your observation, and clearly identify the appears of reactants and products.
Double Displacement Reaction
Watch the following video: https://www.youtube.com/watch?v=X2mB-q2NQXY
Write out the balanced chemical equation for the double replacement reaction of lead nitrate and potassium iodide:
Describe the color of each aqueous solution of reactants lead nitrate and potassium iodide:
Describe the color and state of each product (note, there are two products you will need to describe the color and state of). Recall, by “state” we mean aqueous (aq), gas (g), liquid (l), and solid (s).
Week 5 Assignment – Part B
1. Balance the following chemical equation:
___FeBr3+___H2SO4?___Fe2SO43+___HBr
2. Balance the following chemical equation:
___C7H16+___O2?___CO2+___H2O
3. What is the formula weight (in amu) for ammonia, NH3?
4. How many molecules are present in one mole of water, H2O? Express your answer in scientific notation.
5. A person drinks 1.50 × 103 g of water, H2O, per day. How many moles is this?
6. How many grams of CH3OH are in 0.42 mol CH3OH
6. The balanced equation N2g+3H2(g)?2NH3(g) means which of the following?
One gram of nitrogen reacts with three grams of hydrogen to form two grams of ammonia
One mole of nitrogen reacts with three moles of hydrogen to form two moles of ammonia
The equation means both a and b
The equation means neither a nor b
7. Most of the industrial ammonia today is produced via the Haber Process. The Chemical reaction is one we’ve seen many times now:
N2g+3H2(g)?2NH3(g)
If 20 moles of ammonia (NH3 ) are needed for a particular process, how many moles of diatomic Nitrogen (N2 ) are needed?
Practice with Stoichiometry Calculations – Problem Solving Workflow:
8. How many grams of H2 are required to produce 7.50 grams of ammonia NH3? Use the balanced equation (this time the equation is already balanced):
N2g+3H2g?2NH3(g)
9. If 54.7 grams of propane (C3H8) and 89.6 grams of oxygen (O2) are available in the balanced combustion reaction below:
C3H8+5O2?3CO2+4H2O
a) Which reactant is limiting (show your work)?
b) What is the theoretical yield of CO2 in grams?
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