What are Acids?
The acid in the Latin language means sour. Acids are substances that contain hydrogen and produce hydrogen ions in aqueous solutions. Acids are commonly found in citrus fruits like lemon, tamarind, etc. Citric acid is found in lemon and tartaric acid is found in tamarind. Some of the main acids are hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, acetic acid, formic acid, etc.
We can see many examples of acid in our normal life like the sour taste of all citrus fruits and foods is due to acids like citric acid found in lemon, orange, etc.; acetic acid is found in vinegar, Malic acid is found in apple, tannic acid is found in tea, phosphoric acid is found in carbonated soda, besides hydrochloric acid is used in our body to digest food.
Examples of Acid
Apart from foods, there are many such acids which are used by us domestically or industrially such as sulfuric acid, nitric acid, hydrochloric acid, hydroiodic acid, hydrobromic acid, chloric acid, aqua regia etc.
Interesting Facts about Acids
Acids are sour.
Good and strong acids are good conductors of electricity.
Hydrogen is present in all types of acids.
Acids turn blue litmus red.
The pH level of acids is between 0 and 6.
Acids produce hydrogen gas when reacted with active metals.
Acid carbon dye on reaction with carbonate oxides generate gas. Most acids are corrosive, meaning they are metals. But have the ability to rust or melt them.
Acids react with bases to form salts and water, in this reaction the acid destroys all the chemical properties of the base and also loses its acidity.
An interesting fact about amino acids is that they can also be used by the body as a source of energy.
Litmus Paper and pH scale as an Indicator
Fun Facts about Alkalis
Interesting Facts about Bases (Alkalis)
Alkali is those compounds of metals or radicals that behave like metals, which react with acids to form salts and water.
Alkali is pungent or bitter.
Alkali feels as smooth as soap to the touch.
A strong base is a good conductor of electricity.
The base turns red, litmus blue, and methyl orange in yellow.
Alkali can dissolve oil and sulphur.
Bases turn phenolphthalein pink.
Bases usually precipitate metal hydroxides when added to a salt solution.
Solved Questions
1. How does the colour of litmus change in acidic and alkaline mediums?
Ans: The colour of litmus is red in an acidic medium and blue in an alkaline medium.
2. Write one difference between acid and base.
Ans: Difference between an acid and a base:
Acid - An acid is a substance whose aqueous solution tastes sour.
Base - A base is a substance whose aqueous solution tastes bitter.
Learning By Doing
Write True or False.
Acids are sour.
Good and strong acids are bad conductors of electricity.
Acids turn blue litmus green.
The pH level of acids is between 0 and 6.
Hydrogen is present in all types of acids.
Summary
Acids are substances that contain hydrogen and produce hydrogen ions in aqueous solutions. Acids are commonly found in citrus fruits like lemon, tamarind, etc. Acids are sour. Good and strong acids are good conductors of electricity. Hydrogen is present in all types of acids. Acids turn blue litmus red. Acids react with bases to form salts and water.
FAQs on Facts About Acids
1. What is an acid according to the Arrhenius theory?
According to the Arrhenius theory, an acid is a substance that ionises when dissolved in water to produce hydrogen ions (H⁺) as the only positive ions. This property is what gives acids their characteristic traits, such as a sour taste, which is evident in foods like lemons and vinegar.
2. What are five key characteristics of an acid?
Acids exhibit several distinct characteristics that help in their identification. Five key properties are:
- They have a sour taste.
- They turn blue litmus paper red.
- Their pH value is always less than 7.
- They react with active metals, such as zinc and magnesium, to produce hydrogen gas.
- They react with bases in a neutralisation reaction to form salt and water.
3. Can you give some examples of strong and weak acids found in everyday life?
Yes, acids are categorised as strong or weak based on how completely they ionise in water. Common examples include:
- Strong Acids: Hydrochloric acid (HCl), found in our stomach for digestion, and sulfuric acid (H₂SO₄), used in car batteries.
- Weak Acids: Acetic acid (CH₃COOH), the main component of vinegar; citric acid, found in citrus fruits like lemons; and carbonic acid (H₂CO₃), which gives carbonated drinks their fizz.
4. How do indicators like litmus and phenolphthalein help identify an acid?
Indicators are substances that change colour in the presence of an acid or a base. To test for an acid:
- Litmus paper: A blue litmus paper will turn red when it comes into contact with an acidic solution.
- Phenolphthalein: This synthetic indicator remains colourless in an acidic or neutral solution.
5. What happens when an acid reacts with a metal?
When an acid reacts with an active metal, it typically produces a metallic salt and liberates hydrogen gas. This is a characteristic chemical property of acids. For example, when zinc metal reacts with hydrochloric acid, it forms zinc chloride (a salt) and hydrogen gas.
6. Why are acids good conductors of electricity in their aqueous solutions?
Acids are good electrical conductors in water because they dissociate into mobile ions. When an acid is dissolved in water, it releases positively charged hydrogen ions (H⁺) and negatively charged anions. The presence of these free-moving charged particles allows the solution to carry an electric current. Strong acids are better conductors as they ionise more completely, creating a higher concentration of ions.
7. If all acids contain hydrogen, does that mean all compounds containing hydrogen are acidic?
No, this is a common misconception. While all acids contain hydrogen, not all hydrogen-containing compounds are acids. For a substance to be acidic, its hydrogen atom must be ionisable, meaning it can be released as a proton (H⁺ ion) in solution. For example, methane (CH₄) and glucose (C₆H₁₂O₆) both contain hydrogen, but they do not release H⁺ ions in water and are therefore not classified as acids.
8. How does the acid in our stomach help with digestion without damaging the stomach lining?
Our stomach contains hydrochloric acid (HCl), a strong acid that kills harmful bacteria and provides the acidic environment needed for digestive enzymes like pepsin to function. The stomach protects itself from this corrosive acid with a thick, specialised layer of mucus. This mucus lining acts as a physical barrier, preventing the acid from coming into direct contact with the stomach wall.
9. What is the fundamental difference between an acid and a base in terms of the ions they produce in water?
The primary chemical difference between acids and bases lies in the specific ions they generate when dissolved in water.
- An acid is a substance that increases the concentration of hydrogen ions (H⁺) in a solution.
- A base is a substance that increases the concentration of hydroxide ions (OH⁻) in a solution.
This ionic difference is the basis for their opposing properties and their ability to neutralise each other.
