# Exercises

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## Q7-1

What (in your own words) do you mean when you say a chemical reaction?

## Q7-2

Give some examples of reactions that you know – or have learned about in previous courses.

## Q7-3

Are there any reactions going on around you right now? If so what are they?

## Q7-4

Can you classify or sort the reactions that you have noted? What criteria would you use to classify them?

## Section 7-2

For each reaction use the following steps to write the equation for the reaction that actually occurs.

eg: NaOH(aq) + H2SO4

1. Complete and balance the reaction (this means you have to recognize that this is an Arrhenius acid base reaction – so that the product is water + whatever else is still in solution. (there is a complication that the other ions may precipitate but we will get to that shortly)

2NaOH(aq) + H2SO4(aq) à Na2SO4 (aq) + H2O(l)

1. Write out the ions that are in solution (both as reactants or products).

2Na+(aq) + 2OH(aq) + 2H+(aq) + SO42–(aq) à H2O(l) + 2Na+(aq) + SO42–(aq)

1. Cancel out the spectator ions (those on both sides that are the same)

2Na+(aq) + 2OH(aq) + 2H+(aq) + SO42–(aq) à H2O(l) + 2Na+(aq) + SO42–(aq)

1. Write the equation for the reaction that actually occurs.

2OH(aq) + 2H+(aq) à H2O(l)

## Practice with these reactions.

A) HCl + NaOH

B) HNO3 + Ca(OH)2

C) H2SO4 + KOH

D) H3PO4 + Ca(OH)2 (note the “salt” from this reaction is insoluble – why is that?)

## Q7-2

The next thing we will be doing is to compare the different models of acid base – so you might want to think about how each of these reactions can be considered as Bronsted-Lowry acid base reactions.

## Q7-1

Draw Lewis structures for:

Hydrochloric acid: HCl

Nitric Acid: HNO3

Sulfuric acid: H2SO4

Acetic acid: CH3COOH

What do they all have in common?

Now draw out the conjugate base for each acid. What do they all have in common?

## Q7-1

1. For each comparison, which compound is more basic? Make sure you explain your reasoning. vs.  vs. ## Q7-2

Why did we not include CH4 or Neon in this analysis of acid/base?

## Q7-3

Do you think compounds with ammonium (NH4+) are basic? Why or why not?

## Q7-4

Draw the arrow pushing for this reaction and predict the product produced.

NH3 + BF3

## Q7-1

Which is a stronger acid: NH3 or H2O? Explain

## Q7-2

Which is a stronger base: NH3 or H2O? Explain

## Q7-3

Draw and label representations of

A) A concentrated solution of a strong acid:

B) A dilute solution of a strong acid:

C) A concentrated solution of a weak acid:

D) A dilute solution of a weak acid:

## Q7-1

Explain the reaction of HCl and NaOH in terms of:

A) Arrhenius acid base theory

B) Bronsted-Lowry acid base theory

C) Lewis acid base theory.

## Q7-2

Why do we have different theories to explain the same reaction?

## Q7-3

Give an example of an acid base reaction that can only be explained in terms of Lewis acid base theory. Explain.

## Q7-1

Calculate the pH of:

A) O.25 M HCl

B) 12 M HCl

C) 0.0001 HCl

D) 0.25 NaOH

E) 12 M NaOH

F) 0.0001 NaOH

## Q7-2

A) If the pH of a 0.01 M solution of an acid is 3.56, what does that tell you about the strength of the acid? How do you know?

B) What percent of the above acid is ionized? (See slides)

## Q7-3

Looking at your answer to Q 1part e – how much sodium hydroxide would you need to dissolve in a liter of solution to make a solution with a pH of 16?

## Section 7-9

For the following two questions:

A) Write the balanced equation.

B) Construct the pathway of how you would approach the problem using the map below. Please indicate on the map your groups’ chosen path.

C) Write out the calculation.

D) Calculate.

## Q7-1

What mass Na2CO3 will completely react with 150 mL of 0.15 M HNO3? ## Q7-2

What mass of CO2 will be produced by burning 10 kg octane? ## Q7-1

Calculate:

A) The formal charge for oxygen in H2O and H3O+

B) The oxidation number for oxygen in H2O and H3O+

C) What is the difference between the two?

## Q7-2

What is the oxidation number of each atom in:

A) H2SO4

B) CF4

## Q7-3

For each reaction, decide whether the reaction is a redox reaction by calculating the oxidation number of atoms that take part in the reaction and seeing if that number changes during the reaction. Indicate which species are oxidized and which are reduced. You may need to draw out the structures.

A) CH4 + O2 à CO2 + 2H2O

B) 2Fe(s) + 3S(s) à Fe2S3

C) NH3 + HCl à NH4Cl

D) CH3Br + NH3 à CH3NH2 + HBr

E) CaCl2(aq) + AgNO3(aq) à AgCl(s) + Ca(NO3)2(aq)

## Q7-1

A) What happens to the potential energy of a system when two atoms approach each other and form a bond?

B) What happens to the kinetic energy of the system?

C) What happens to the total energy of the system?

D) What happens to the energy of the two atom system if there are more than two atoms?

## Q7-2

When a bond between two atoms is broken is there a change in energy of the system?

## Q7-3

When CH4 reacts with O2 à CO2 + H2O (a combustion reaction). There is an energy change. Where does that energy come from? Where does it go?

## Q7-1

Use the table of bond energies to calculate the enthalpy change (ΔH) for these reactions. A) C2H4 + H2 à C2H6

B) CH4 + 4Br2 à CBr4 + 4HBr

C) CH3Br + OH à CH3OH + Br

## Q7-2

For many Bronsted acid base reactions (eg NaOH + HCl, or KOH + HNO3) the enthalpy change is the same regardless of which acid and which base are used. Why do you think this is so?

## Q7-3

When you calculate (ΔH) using Bond Energies, you often get a slightly different answer, than if you do a calorimetry experiment (See chapter 5), and experimentally determine ΔH. Why do you think this is so?

## Q7-1

For each reaction identify the Lewis acid and Lewis base. Draw the curved arrows that show the direction of electron flow and show the structure of the product(s) you would expect. (you will need to draw out the Lewis structures)

A) HCl + NH3

B) BF3 + H2O

## Q7-2

Now identify the nucleophiles and electrophiles in these reactions to predict the products of these reactions.

For each reaction draw the curved arrows that show the direction of electron flow and show the structure of the product(s) you would expect.

A) CH3Br + NH3

B) CH3CH2Br + CH3NH2

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