Chemical Reactions Lab Worksheet

INTRODUCTION

Atoms gain or lose electrons to yield ions, or combine with other atoms to form molecules. The symbols of atoms are combined to represent the chemical compounds that are formed. A chemical reaction is when one or more substances undergo a chemical change to form new substance(s). There are several observations that are evidence of a chemical reaction. Some of these possible observations are the production of a gas, the formation of a precipitate, a color change, or even an energy change in the form of heat. One chemical reaction that you’ve performed several times already is the combustion of methane (CH4). The combustion of methane results in the following observations: light is emitted, heat is emitted, and water vapor is released.

 

In chemistry, it is important that we can represent each chemical reaction in terms of the atoms involved. A chemical equation represents the chemical or physical change that take place including the identities and the relative quantities of the chemical substances. For example, when one methane molecule (CH4) and two diatomic oxygen molecules (O2) react, one carbon dioxide molecule (CO2) and two water molecules (H2O) are formed. This reaction is represented in Figure 1 below using a chemical equation and a space-filling model.

 

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Figure 1: Chemical Equation and Space-Filling Model for the Formation of Methane

 

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There are four fundamental aspects to any chemical equation:

  1. The substances that are on the left side of the equation are known as reactants, and they are the substances undergoing reaction.
  2. The substances on the right side of the equation are known as products, and they are the substances generated by the reaction.
  3. Plus signs (+) separate individual reactants and products, while an arrow (→) separates the left side (reactants) and right side (products) of a reaction.
  4. The relative number of products and reactants for a particular reaction are represented using coefficients, the numbers to the left of each chemical formula. When the coefficient is 1, the number is typically omitted. These coefficients are reduced to the lowest whole-number ratio in a chemical equation. Because matter is not created or destroyed by a chemical reaction, the numbers of atoms must be the same on either side of the reaction. The atoms are ‘balanced’ by adjusting the chemical coefficients of the reactants and products.

 

In addition to these basic features of a chemical equation, various symbols are used to describe a chemical reaction.

  1. Each reactant and product must have an indicated state of matter. Solids or precipitates are represented by (s), liquids by (l), gases by (g), and aqueous solutions as (aq).
  2. If a reaction does not take place, NR (which stands for ‘No Reaction’) is written after the → in a reaction.
  3. If heat is used in a reaction, the symbol ∆ is written above the →

 

There are five basic types of chemical reactions: combination, combustion, single displacement, double displacement, and decomposition reactions. Neutralization, acid-base, and gas-forming reactions are reactions that can also be classified as double-displacement reactions.

 

Single-displacement reactions occur when one element displaces another in a compound. All single displacement reactions have the general form:

 

A + BC B + AC

 

Example of a single displacement reaction:

 

Zn(s) + 2 HCl(aq) → ZnCl2(aq) + H2(g)

 

There are multiple types of double-displacement reactions, reactions with the form:

 

AB + CD AD + CB

 

The first type, a precipitation reaction, occurs when the cations and anions of aqueous ionic compounds switch partners, forming the two new ionic compounds, AD and CB. One of the new ionic compounds formed is an insoluble solid compound, known as a precipitate. To determine whether the product of a precipitation reaction will be soluble or insoluble, Solubility Rules (shown below), are consulted.

 

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Example of a double displacement reaction:

 

3AgNO3(aq) + Na3PO4(aq) → Ag3PO4(s) + 3NaNO3(aq)

 

The second type, a neutralization reaction, occurs when an acid and base react to form an ionic compound (salt) and liquid water. Acid-base reactions are exothermic, so energy is released as heat upon reaction.

 

Example of a neutralization reaction:

 

H2SO3(aq) + 2 NaOH(aq) → Na2SO3(aq) + 2 H2O(l)

 

 

The third type, a gas-forming reaction, has an unstable product, which will decompose into at least one gas as a product.

 

Example of a gas-forming reaction:

 

2 HNO3(aq) + Na2SO3(aq) → 2 NaNO3(aq) + H2O(l) + SO2(g)

 

In this laboratory, we are going to perform a series of chemical reactions, and record evidence of a reaction such as the formation of gas, the formation of a precipitate, a change in color, or a change in temperature. These reactions will then be classified as single displacement, double-displacement, neutralization, or gasforming. You will then the write and balance chemical equations and practice predicting the products of the reactions introduced in this laboratory.

 

A lot of reactions take place in aqueous media (water), and subsequently involve ions. The balanced equation is called the molecular equation, and is written in the usual way as the reactions above. The reaction below will be used as an example.

 

BaBr2(aq) + Pb(NO3)2(aq)  Ba(NO3)2(aq) + PbBr2(s)

 

When ionic compounds are dissolved in water, they dissociate into their parent ions, and this equation is referred to as the complete ionic equation. Be careful to remember that only aqueous ionic compounds dissociate into ions – solids, liquids, and gases cannot be dissociated as they are not in solution.

 

Ba2+(aq) + 2Br_(aq) + Pb2+(aq) + 2NO3(aq)  Ba2+(aq) + 2NO3(aq) + PbBr2(s)

 

When two identical chemical species are on each side of the equation they are known as spectator ions, and can be eliminated from the equation. The equation that remains after the spectator ions have been removed and is referred to as the net ionic equation.

 

Ba2+(aq) + 2Br_(aq) + Pb2+(aq) + 2NO3(aq)Ba2+(aq) + 2NO3(aq) + PbBr2(s)

 

 

2Br_(aq) + Pb2+(aq)  PbBr2(s)

 

 

 

 

 

PROCEDURE:

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  1. You may want to refer to your prelab for the formulas of each reactant.
  2. For the reactions involving solid reactants, use large test tubes and place in a beaker to observe the reaction. For reactions involving solutions, use small (10 mL) test tubes and the red test tube racks from the “151 Cart.”. Use test tubes that are clean and rinsed with distilled water. It is not necessary for the test tubes to be dry.
  3. When using solutions, use approximately 1.5 mL of each solution. When mixing two solutions, there should be a total of 3 mL, which is indicated by red tape on a sample test tube by the fume hood.
  4. When using metals, use 1 piece of the copper and magnesium metal and 2 pieces of zinc, putting the metal in the test tube, then put the solution in the test tube. The metal should be fully immersed in solution.
  5. Perform the reactions below, record your observations in the table below, specify the type of reaction that was completed, and write the balanced molecular equation.

 

DATA:

 

Reactants

Observation(s)

Type of Reaction

Balanced Molecular Equation

aqueous barium

chloride + aqueous sodium sulfate

A white solid forms after the solutions are mixed together.

Precipitation Reaction

BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2 NaCl(aq)

zinc metal + hydrochloric acid

 

 

Bubbles are observed after the solutions are mixed together. The

zinc appears to be smaller in size.

 

 

 

 

 

 

aqueous sodium

phosphate + aqueous copper(II) sulfate

 

 

 

A solid forms after the solutions are mixed together.

 

 

 

 

 

copper metal + aqueous silver nitrate

 

 

 

After the solution is added to the copper, the copper turns black and pieces of it are following off.

 

 

 

 

Solid sodium bicarbonate + aqueous acetic acid

 

 

 

When acetic acid is poured on the solid, bubbles are formed, and the solution looks frothy.

 

 

 

 

 

aqueous nickel(II) nitrate + aqueous sodium hydroxide

 

 

 

A solid forms after the solutions are mixed together.

 

 

 

 

 

 

aqueous potassium chloride + aqueous silver nitrate

 

 

 

A solid forms after the solutions are mixed together.

 

 

 

 

 

aqueous hydrochloric acid + aqueous sodium hydroxide

 

 

 

A clear solution is observed after the solutions are mixed together.

 

 

 

 

 

aqueous sodium

carbonate + aqueous cobalt(II) nitrate

 

 

 

A solid forms after the solutions are mixed together.

 

 

 

 

 

 

zinc metal + aqueous lead(II) nitrate

 

 

 

The zinc metal looks as if it is corroding when the solution is added.

 

 

 

 

 

magnesium metal +

aqueous acetic acid

 

 

 

When the solution is added, bubbles form around/on the metal.

 

 

 

 

aqueous iron(III)

chloride + aqueous ammonium hydroxide

 

 

 

A yellow solid forms after the solutions are mixed together.

 

 

 

 

 

 

 

POST-LABORATORY QUESTIONS

 

1. For the following reactions, write the balanced molecular equation, complete ionic equation, and net ionic equation.

 

  1. barium chloride(aq) + sodium sulfate(aq) →

 

Balanced Molecular Equation:

Complete Ionic Equation:

 

 

 

Net Ionic Equation:

 

 

 

 

 

 

 

 

  1. nitric acid(aq) + sodium hydroxide(aq) →

 

Balanced Molecular Equation:

 

 

 

 

 

Complete Ionic Equation:

 

 

 

 

 

Net Ionic Equation:

 

 

 

 

PRE-LABORATORY ASSIGNMENT

 

  1. What are the three observations that a chemical reaction has occurred?

 

 

 

 

 

  1. What are the types of reactions we are performing in this laboratory? Describe them in detail.

 

 

 

 

 

 

 

  1. Write the general reactions for single and double displacement reactions.

 

 

 

 

  1. You will be using the reactants below in this lab. Write the chemical formula for each name.

Chemical Formula

Name

Chemical Formula

Name

Barium chloride

BaCl2

Potassium chloride

 

Sodium sulfate

 

Cobalt(II) nitrate

 

Hydrochloric acid

 

Sodium carbonate

 

Sodium phosphate

 

Lead(II) nitrate

 

Copper(II) sulfate

 

Sodium chloride

 

Silver nitrate

 

Potassium nitrate

 

Acetic acid

 

Iron(III) chloride

 

Nickel(II) nitrate

 

Ammonium hydroxide

 

Sodium hydroxide

 

Sodium bicarbonate

 

Zinc nitrate

 

 

 

  1. Translate the following word equations into balanced chemical equations.
  2. copper(s) + silver nitrate(aq) → copper(II) nitrate + silver(s)
  3. calcium(s) + water(l) → calcium hydroxide(s) + hydrogen(g)
  4. aluminum nitrate(aq) + potassium carbonate(aq) → aluminum carbonate(s) + potassium nitrate(aq)
  5. sulfuric acid(aq) + potassium hydroxide(aq) → potassium sulfate(aq) + water(l)

 

 

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