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# Reactions of Acids

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Did you know that acids are a big part of our diets? Many fruits including oranges and lemons, dairy products, fish and meat, cocoa, starchy foods like wheat, and carbonated drinks (soda, cola) all contain some acids in it. The gastric juice used by the digestive system to digest food has hydrochloric acid as its key component. So, it seems important to know how different acids react with different substances. This is what we will discuss in this article.

• In this article, you will learn about how acids react with metals.
• How acids react with metal hydroxides.
• How acids react with metal Carbonates and Bicarbonates.
• How acids react with weak weak bases.

In an aqueous solution, acids ionise to give H+ cation and an anion.

An aqueous solution is any solution in which water is the solvent i.e., a solution in which water is used to dissolve something.

Mixing table salt in water makes an aqueous solution of salt. Similarly, mixing coffee in water makes an aqueous solution.

Consider an arbitrary acid HA. The acid HA ionizes in an aqueous solution like this -

$$HA\rightarrow H^{+}+A^{-}$$

Here, H+ is a hydrogen ion, and A- is any anion. The anion in the acid (A- ) can be either monoatomic or polyatomic. Monoatomic anions can be chloride (Cl-), bromide (Br-) etc. Polyatomic anions consist multiple atoms, like nitrate (NO3-), sulphate (SO42-), carbonate (CO32-).

Acids are chemical substances which taste sour in an aqueous solution, are corrosive, and turn blue litmus paper to red.

Acids are substances which either release proton (H+) in an aqueous solution, or form a covalent bond with a non bonding electron pair of another molecule.

The acids which release H+ ions are called Bronsted-Lowry acids.

The acids which form a covalent bond with a non bonding electron pair of another electron (accept an electron pair) of another molecule are called Lewis acids.

## Strong Acids and Weak Acids

Some acids are strong acids, while some are weak acids. Strong acids are those that ionise completely to give H+ ions in an aqueous solution. Weak acids do not ionise completely in an aqueous solution. A solution with some amount of weak acid will be less acidic than a solution with the same amount of a strong acid.

The acidity of a solution is measured on a pH scale. The pH scale varies from 0 to 14. Solutions with pH < 7 are acidic, solutions with pH > 7 are basic, and pH = 7 indicates neutral solution. Water has a pH of 7. Very strong acids have a pH of 0 (hydrochloric acid with a concentration of 1 mol L-1). Similarly, very strong bases have a pH of 14 (sodium hydroxide with a concentration of 1 mol L-1).

The pH of a solution is lower (more acidic) if the concentration of H+ ions is more. A weak acid does not ionise completely in an aqueous solution, therefore concentration of H+ ions is less, therefore, pH is less. That is why it less acidic than a solution with the same amount of strong acid.

Some examples of acids are:

• Hydrochloric Acid HCl (strong).
• Hydrobromic acid HBr (strong).
• Nitric acid HNO3 (strong).
• Sulphuric acid H2SO4 (strong).
• Sulphurous acid H2SO3 (weak).
• Carbonic acid H2CO3 (weak).
• Acetic acid CH3COOH (weak).

All acids react in a similar way with particular substances. We will be studying these general reactions of acids, which include -

• Reaction of acids with metal hydroxides.
• Reaction of acids with metals.
• Reaction of acids with metal carbonates and bicarbonates.
• Reaction of acids with weak bases.

## Reaction of Acids with Metal Hydroxides

Metal Hydroxides are chemicals which neutralize acids. All metal hydroxides are bases, or alkalis.

Bases are substances which taste bitter in an aqueous solution, are slippery to touch, and change the colour of blue litmus paper to red. Bases release hydroxide ions (OH-) in an aqueous solution.

Alkalis are bases that are soluble in water. All alkalis are bases, but all bases are not alkalis.

When an acid reacts with a base, the reaction produces salt and water. sodium chloride (key component of table salt) is produced by the reaction of hydrochloric acid and sodium hydroxide, a base.

$$acid\ +\ metal\ hydroxide\ \rightarrow salt\ +\ water$$

In chemistry, a salt is an ionic compound which consists of a cation (positive ion) which comes from a base, and a anion (negative ion) which comes from an acid.

Sodium chloride (NaCl), a key component in table salt, can be produced with the reaction of hydrochloric acid (HCl) which is an acid, and sodium hydroxide (NaOH), which is a base.

Reaction of hydrochloric acid and sodium hydroxide produces sodium chloride, a salt which is the main component of table salt used in cooking.

$$HCl+NaOH\rightarrow NaCl+H_{2}O$$

The hydrogen ion H+ from the acid, and the hydroxide ion OH- from the base, combine to form water. While the anion from the acid, and the cation from the base combine to form salt. Take a look at another acid-base reaction -

$$H_{2}SO_{4\ (aq)}+Cu(OH)_{2}\rightarrow CuSO_{4}+2H_{2}O$$

Sulphuric acid reacts with copper hydroxide to produce copper sulphate and Water. The anion in sulphuric acid is sulphate (SO4-), and the cation in copper hydroxide is copper (Cu2+). Now, let's look at another type of acid reacting with a base -

$$HNO_{3}+NaOH\rightarrow NaNO_{3}+H_{2}O$$

HNO3 is nitric acid. When it reacts with the base sodium hydroxide (NaNO3), sodium nitrate (NaNO3) salt is produced.

Points to be remembered about reaction of acids and bases:

• Reaction of hydrochloric acid with a base will produce chloride salts, like sodium chloride (NaCl), copper chloride (CuCl2) etc.
• Reaction of sulphuric acid with a base will produce sulphate salts, like sodium sulphate (NaSO4), copper sulphate (CuSO4) etc.
• Reaction of nitric acid with a base will produce nitrate salts, like sodium nitrate (NaNO3), copper nitrate (CuNO3) etc.

## Reactions of Acids with Metals

Acids react with metals to give a salt and Hydrogen gas.

$$Acid\ +\ Metal\rightarrow Salt+H_{2\ (g)}$$

The metal forms a compound with the anion released by the acid, and the H+ cation released combine to form hydrogen.

Let us take the example of reaction of hydrogen chloride with magnesium.

$$HCl_{(aq)}+Mg_{(s)}\rightarrow MgCl_{2\ (aq)}+H_{2\ (g)}$$

Hydrochloric acid ionizes into hydrogen ions (H+) and chloride (Cl-) ions. Solid magnesium reacts with the acid to form magnesium chloride, and hydrogen gas is evolved.

While performing this reaction in a test-tube in the chemistry lab, you can test for the hydrogen gas released by bringing a lighted splint near the test-tube. Hydrogen is highly inflammable and you will hear a popping sound as the hydrogen release ignites due to the lighted splint.

Since the reaction of acid with metals is spontaneous (it happens automatically without any aid of heat or a catalyst), acids are considered corrosive to metals. Metals loose their properties when they react with acids to form salts. This can cause damage to structures or objects which are made of metal. This is called corrosion of metals.

Keep in mind that the reaction of metals with acid is not called corrosion, it only causes the corrosion.

## Reaction of Acids with Metal Carbonates and Metal Hydrogen Carbonates

Metal carbonates are compounds which have a metal as cation and a carbonate ion (CO32-) for anion. Acids react with metal carbonates to produce salt, water, and carbon dioxide.

$$Acid\ +\ Metal\ carbonate\ \rightarrow Salt\ +\ Water\ + CO_{2\ (g)}$$

As an example, look at the reaction of hydrochloric acid an copper carbonate:

$$2HCl_{(aq)}+CuCO_{3 (s)}\rightarrow CuCl_{2\ (aq)}+H_{2}O_{(l)}+CO_{2\ (g)}$$

The products are are similar to as if hydrochloric acid was reacting with copper hydroxide (Cu(OH)2), with an extra product of carbon dioxide which is evolved due to the presence of the carbonate group. Let us look at another example:

$$HBr_{(aq)}+MgCO_{3(s)}\rightarrow MgBr_{2(aq)}+H_{2}O_{(l)}+CO_{2(g)}$$

The acid in above reaction is hydrogen bromide (HBr), and it is reacting with magnesium carbonate (MgCO3). The salt produced is magnesium bromide (MgBr2)

Metal hydrogen carbonates are chemicals which have a metal for the cation, and HCO3- for the anion. Metal hydrogen carbonates are also called metal bicarbonates.

$$Acid\ +\ Metal\ bicarbonate\rightarrow Salt\ +\ Water\ +\ CO_{2 (g)}$$

Metal bicarbonates react with acids to produce the same products as metal carbonates.

$$HCl_{(aq)}+NaHCO_{3(s)}\rightarrow NaCl_{(aq)}+H_{2}O_{(l)}+CO_{2(g)}$$

In the reaction above, hydrochloric acid reacts with sodium bicarbonate (NaHCO3) to produce sodium chloride salt, along with water and carbon dioxide gas. Look at another example - reaction of potassium bicarbonate with nitric acid.

$$HNO_{3(aq)}+KHCO_{3(s)}\rightarrow KNO_{3(aq)}+H^{2}O_{(l)}+CO_{2(g)}$$

The salt produced in this reaction is potassium nitrate (KNO3), and as usual, carbon dioxide gas is released.

## Reaction of Acids with Weak Bases

Acids neutralise weak bases, just like they do strong bases. But some weak bases do not contain hydroxide (OH-), and so do not produce water when reacting with acids.

$$Acid\ +\ Weak base\ \rightarrow Salt\ +\ Water$$

Ammonia is an example of a weak base.

$$HCl_{(aq)}+NH_{3(g)}\rightarrow NH_{4}Cl_{(aq)}$$

reaction of ammonia with hydrochloric acid produces ammonium chloride.

Unlike many other bases, it does not contain a hydroxide ion (OH-). Ammonia has a high affinity for a proton i.e. it readily accepts an H+ ion. Ammonia gains an H+ ion to become ammonium ion (NH4+). Acids react with with ammonia to produce ammonium salts.

Can you guess what will be the product if ammonia reacts with sulphuric acid?

$$H_{2}SO_{4(aq)}+2NH_{3(g)}\rightarrow (NH_{4})_{2}SO_{4(aq)}$$

The above reaction is of sulphuric acid and ammonia. Ammonium sulphate salt is produced in the reaction.

Another example of weak base is aluminium hydroxide. Reaction of Al(OH)3 with an acid produces salt and water.

$$HCl+Al(OH)_{3}\rightarrow AlCl_{3}+H_{2}O$$

## Reactions of Acids - Key takeaways

• An acid ionises in water to give an anion, and a hydrogen ion (H+), which is a cation.
• The anion released by an acid can be monoatomic or polyatomic depending on the chemical composition of the acid.
• Monoatomic anions include (but are not limited to) chloride (Cl-), bromide (Br-), fluoride (F-). Polyatomic anions include (but are not limited to) nitrate (NO3-), sulphate (SO42-), carbonate (CO32-).
• Some examples of acids are:
• Hydrochloric acid HCl.
• Hydrobromic acid HBr
• Nitric acid HNO3.
• Sulphuric acid H2SO4.
• Sulphurous acid H2SO3.
• Carbonic acid H2CO3.
• Acids react with bases to produce salt and water.
• A salt is a chemical which consists of a cation (positive ion) which comes from a base, and a anion (negative ion) which comes from an acid.
• Acids react with metals to produce salt and hydrogen gas.
• Reaction of metal with an acid causes corrosion of metal.
• Reaction of acids with metal carbonates as well as metal bicarbonates produces salt, water, and carbon dioxide gas.
• Reaction of acids with ammonia produces ammonium salts.

## Frequently Asked Questions about Reactions of Acids

General reactions of acids include -

• Reaction of acids with Bases and Alkalis
• Reaction of acids with Metals
• Reaction of acids with Metal Carbonates and Bicarbonates
• Reaction of acids with Ammonia

An example of a reaction of acid is the reaction of Hydrochloric acid with Sodium Hydroxide. This reaction produces Sodium Chloride (salt) and water.

HCl(aq) + NaOH(aq) → NaCl2(aq) + H2O(l)

The reaction of magnesium and hydrochloric acid produces Magnesium Chloride (salt), and Hydrogen gas is evolved.

HCl(aq) + Mg(s) → MgCl2(aq) + H2(g)

Following are 4 examples of acids -

• Hydrobromic acid HBr
• Nitric acid HNO3
• Sulphuric acid H2SO4
• Sulphurous acid H2SO3

Sodium Chloride and water.

HCl + NaOH → NaCl + H2O

## Reactions of Acids Quiz - Teste dein Wissen

Question

Which acid is produced by the digestive system to digest food?

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Answer

Hydrochloric acid

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Question

What is an aqueous solution?

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Answer

A solution in which something is dissolved in water. Water is the solvent in an aqueous solution.

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Question

What are the products of the reaction of an acid with a base?

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Answer

Salt and water

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Question

What is a salt in chemistry?

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Answer

In chemistry, a salt is an ionic compound which consists of a cation (positive ion) which comes from a base, and a anion (negative ion) which comes from an acid.

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Question

What salt is produced by the reaction of Hydrochloric acid and Sodium Hydroxide?

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Answer

Sodium Chloride (NaCl)

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Question

What is the main component of table salt?

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Answer

Sodium Chloride (NaCl)

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Question

Which gas is evolved when an acid reacts with a metal?

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Answer

Hydrogen gas

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Question

When a metal reacts with an acid, it  undergoes _____.

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Answer

Corrosion

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Question

Which gas is evolved when an acid reacts with a metal carbonate?

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Answer

Carbon Dioxide

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Question

What are the products of the reaction of acids with metal bicarbonates?

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Answer

Salt, water, and Carbon Dioxide gas.

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Question

Metal bicarbonates are also called _____.

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Answer

Metal hydrogencarbonates

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Question

What will be the product of the reaction of Ammonia with Nitric acid?

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Answer

Ammonium Nitrate

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