Chemistry » Acid-Base and Redox Reactions » Acid-Base Reactions Continued

# More on Acid-Base Reactions

## Optional Activity: Acids and metal compounds

Research the reactions that occur when an acid is added to the following compounds:

• a metal

• a metal hydroxide

• a metal oxide

• a metal carbonate

• a metal hydrogen carbonate

Write a report which includes:

• The general equation (in words) of each reaction.

• A description of what is happening in this reaction.

• An example of this type of reaction in the form of a balanced equation.

### Sample Report:

The following is an example of how your acids and metals compounds report could look:

• Acid + metal $$\to$$ salt + hydrogen

A dilute acid is added to a pure metal to form a salt and hydrogen gas. The salt is formed by the metal cation and the anion from the acid. In this reaction the metal is acting as a base. For example:

$$\color{red}{\text{hydrochloric acid}} + \color{blue}{\text{zinc}} \to \color{blue}{\text{zinc}} \color{red}{\text{ chloride}}$$ + hydrogen

$$2\text{HCl}(\text{aq}) + \text{Zn}(\text{s})$$ $$\to$$ $$\text{ZnCl}_{2}(\text{aq}) + \text{H}_{2}(\text{g})$$

• Acid + metal hydroxide $$\to$$ salt + water

A dilute acid is added to a metal hydroxide to form a salt and water. The salt is formed by the metal cation and the anion from the acid. In this reaction the metal hydroxide is acting as a base. For example:

$$\color{red}{\text{hydrochloric acid}} + \color{blue}{\text{zinc hydroxide}} \to \color{blue}{\text{zinc}} \color{red}{\text{ chloride}}$$ + water

$$2\text{HCl}(\text{aq}) + \text{Zn}(\text{OH})_{2}(\text{s})$$ $$\to$$ $$\text{ZnCl}_{2}(\text{aq}) + 2\text{H}_{2}\text{O}(\text{l})$$

• Acid + metal oxide $$\to$$ salt + water

A dilute acid is added to a metal oxide to form a salt and water. The salt is formed by the metal cation and the anion from the acid. In this reaction the metal oxide is acting as a base. For example:

$$\color{red}{\text{hydrochloric acid}} + \color{blue}{\text{zinc oxide}} \to \color{blue}{\text{zinc}} \color{red}{\text{ chloride}}$$ + water

$$2\text{HCl}(\text{aq}) + \text{ZnO}(\text{s})$$ $$\to$$ $$\text{ZnCl}_{2}(\text{aq}) + \text{H}_{2}\text{O}(\text{l})$$

• Acid + metal carbonate $$\to$$ salt + water + carbon dioxide

A dilute acid is added to a metal carbonate to form a salt, water and carbon dioxide gas. The salt is formed by the metal cation and the anion from the acid. In this reaction the metal carbonate is acting as a base. For example:

$$\color{red}{\text{hydrochloric acid}} + \color{blue}{\text{zinc carbonate}} \to \color{blue}{\text{zinc}} \color{red}{\text{ chloride}}$$ + water + carbon dioxide

$$2\text{HCl}(\text{aq}) + \text{ZnCO}_{3}(\text{s})$$ $$\to$$ $$\text{ZnCl}_{2}(\text{aq}) + \text{H}_{2}\text{O}(\text{l}) + \text{CO}_{2}(\text{g})$$

• Acid + metal hydrogen carbonate $$\to$$ salt + water + carbon dioxide

A dilute acid is added to a metal hydrogen carbonate to form a salt, water and carbon dioxide gas. The salt is formed by the metal cation and the anion from the acid. In this reaction the metal hydrogen carbonate is acting as a base. For example:

$$\color{red}{\text{hydrochloric acid}} + \color{blue}{\text{zinc bicarbonate}} \to \color{blue}{\text{zinc}} \color{red}{\text{ chloride}}$$ + water + carbon dioxide

$$2\text{HCl}(\text{aq}) + \text{Zn}(\text{HCO}_{3})_{2}(\text{s})$$ $$\to$$ $$>\text{ZnCl}_{2}(\text{aq}) + 2\text{H}_{2}\text{O}(\text{l}) + 2\text{CO}_{2}(\text{g})$$

Yet another optional activity:

## Optional Activity: The hazardous nature of acids and bases

Search for information about the following strong acids and bases:

• Hydrochloric acid ($$\text{HCl}$$)

• Sulfuric acid ($$\text{H}_{2}\text{SO}_{4}$$)

• Sodium hydroxide ($$\text{NaOH}$$)

• Potassium hydroxide ($$\text{KOH}$$)

Write a report which includes:

• The uses of these compounds in industry

• If applicable, the environmental waste that contains these compounds

• What the effect of a large spillage of these compounds would be

### Note:

The following is an example of the sort of information you could report on:

Hydrochloric acid

Hydrochloric acid is used industrially to clean rust from iron or steel as well as in the refining of ores. If released into the environment hydrochloric acid will lower the pH of any water it pollutes. This change in pH can seriously affect the growth of plants and damage ecosystems.

## Example: Determining Equations from Starting Materials

### Question

Magnesium carbonate ($$\text{MgCO}_{3}$$) is dissolved in nitric acid ($$\text{HNO}_{3}$$). Give the balanced chemical equation for this reaction.

### Step 1: What are the reactants?

An acid ($$\text{HNO}_{3}$$) and a metal carbonate ($$\text{MgCO}_{3}$$).

### Step 2: What will the products be?

As this is the reaction of an acid and a metal carbonate the products will be a salt, water and carbon dioxide.

nitric acid + magnesium carbonate $$\to$$ salt + water + carbon dioxide

### Step 3: What is the formula of the salt?

The cation will come from the metal carbonate ($$\text{Mg}^{2+}$$). The anion will come from the acid ($$\text{NO}_{3}^{-}$$). Due to the charges on the cation and anion there must be two $$\text{NO}_{3}^{-}$$ for every one $$\text{Mg}^{2+}$$.

Therefore the formula for the salt will be: $$\text{Mg}(\text{NO}_{3})_{2}$$.

### Step 4: Write the equation for this reaction

$$\text{HNO}_{3}(\text{aq}) + \text{MgCO}_{3}(\text{s})$$ $$\to$$ $$\text{Mg}(\text{NO}_{3})_{2}(\text{aq}) + \text{H}_{2}\text{O}(\text{l}) + \text{CO}_{2}(\text{g})$$

### Step 5: Make sure that the equation is balanced

The equation is not balanced.

 Number on left Number on right H $$\text{1}$$ $$\text{2}$$ N $$\text{1}$$ $$\text{2}$$ O $$\text{6}$$ $$\text{9}$$ Mg $$\text{1}$$ $$\text{1}$$ C $$\text{1}$$ $$\text{1}$$

To balance this equation there needs to be two nitric acid molecules on the left hand side.

$$2\text{HNO}_{3}(\text{aq}) + \text{MgCO}_{3}(\text{s})$$ $$\to$$ $$\text{Mg}(\text{NO}_{3})_{2}(\text{aq}) + \text{H}_{2}\text{O}(\text{l}) + \text{CO}_{2}(\text{g})$$

 Number on left Number on right H $$\text{2}$$ $$\text{2}$$ N $$\text{2}$$ $$\text{2}$$ O $$\text{9}$$ $$\text{9}$$ Mg $$\text{1}$$ $$\text{1}$$ C $$\text{1}$$ $$\text{1}$$

The equation is now balanced.

## Example: Determining Equations from Starting Materials

### Question

Hydroiodic acid ($$\text{HI}$$) is added to solid potassium hydroxide ($$\text{KOH}$$). Give the balanced chemical equation for this reaction.

### Step 1: What are the reactants?

An acid ($$\text{HI}$$) and a base ($$\text{KOH}$$).

### Step 2: What will the products be?

As this is the reaction of an acid and base (which contains a hydroxide anion) the products will be a salt and water.

hydroiodic acid + potassium hydroxide $$\to$$ salt + water

### Step 3: What is the formula of the salt?

The cation will come from the base ($$\text{K}^{+}$$). The anion will come from the acid ($$\text{I}^{-}$$). Due to the charges on the cation and anion there must be one $$\text{K}^{+}$$ for every one $$\text{I}^{-}$$.

Therefore the formula for the salt will be: $$\text{KI}$$.

### Step 4: Write the equation for this reaction

$$\text{HI}(\text{aq}) + \text{KOH}(\text{s})$$ $$\to$$ $$\text{KI}(\text{aq}) + \text{H}_{2}\text{O}(\text{l})$$

This can also be written:

$$\text{HI}(\text{aq}) + \text{KOH}(\text{s})$$ $$\to$$ $$\text{K}^{+}(\text{aq}) + \text{I}^{-}(\text{aq}) + \text{H}_{2}\text{O}(\text{l})$$

### Step 5: Make sure that the equation is balanced

The equation is balanced.

## Example: Determining Equations from Starting Materials

### Question

Sulfuric acid ($$\text{H}_{2}\text{SO}_{4}$$) and ammonia ($$\text{NH}_{3}$$) are combined. Give the balanced chemical equation for this reaction.

### Step 1: What are the reactants?

An acid ($$\text{H}_{2}\text{SO}_{4}$$) and a base ($$\text{NH}_{3}$$).

### Step 2: What will the products be?

As this is the reaction of an acid and a base (with no hydroxide anion), there will be a salt as a product. There may or may not be another product.

sulfuric acid + ammonia $$\to$$ salt (+ maybe another product)

### Step 3: What is the formula of the salt?

The cation will come from the base ($$\text{NH}_{4}^{+}$$). The anion will come from the acid ($$\text{SO}_{4}^{2-}$$). Due to the charges on the cation and anion there must be two $$\text{NH}_{4}^{+}$$ for every one $$\text{SO}_{4}^{2-}$$.

Therefore the formula for the salt will be: $$(\text{NH}_{4})_{2}\text{SO}_{4}$$.

### Step 4: Write the equation for this reaction so far

$$\text{H}_{2}\text{SO}_{4}(\text{aq}) + \text{NH}_{3}(\text{g})$$ $$\to$$ $$(\text{NH}_{4})_{2}\text{SO}_{4}(\text{aq})$$ (+ maybe another product)

### Step 5: Determine if there will be another product

There are no atom types that are not accounted for on both sides of the equation, therefore it is unlikely that there will be another product. If the equation can be balanced then there is no other product.

### Step 6: Make sure that the equation is balanced

The equation is not balanced.

 Number on left Number on right H $$\text{5}$$ $$\text{8}$$ S $$\text{1}$$ $$\text{1}$$ O $$\text{4}$$ $$\text{4}$$ N $$\text{1}$$ $$\text{2}$$

To balance this equation there needs to be two ammonia molecules on the left hand side.

$$\text{H}_{2}\text{SO}_{4}(\text{aq}) + 2\text{NH}_{3}(\text{g})$$ $$\to$$ $$(\text{NH}_{4})_{2}\text{SO}_{4}(\text{aq})$$

 Number on left Number on right H $$\text{8}$$ $$\text{8}$$ S $$\text{1}$$ $$\text{1}$$ O $$\text{4}$$ $$\text{4}$$ N $$\text{2}$$ $$\text{2}$$

The equation is now balanced.