Definitions [13]
Define Acid.
An acid is a compound which when dissolved in water produces hydronium ion(H3O+), the only positively charged
ion and a negative ion.
Acids are defined as compounds which contain one or more hydrogen atoms and when dissolved in water, produce hydronium ions (H3O+) the only positively charged ions.
Define the term ‘basicity’ of an acid.
The basicity of an acid is defined as the number of hydronium ions (H3O+) that can be produced by the ionization of one molecule of that acid in aqueous solution.
Define a base.
A base is defined as a chemical compound that, when it reacts with a hydronium ion or H+ ions furnished by an acid, forms a salt and water only.
An alkali is a basic hydroxide which when dissolved in water produces hydroxyl (OH-) ions as the only negatively charged ions.
A base is either a metallic oxide or a metallic hydroxide or ammonium hydroxide which reacts with hydronium ions of an acid to form a salt and water only.
Mixing an acid or base with water results in decrease in the concentration of ions (H3O+/OH–) per unit volume. Such a process is called dilution and the acid or the base is said to be diluted.
Define pOH.
The pOH of a solution can be defined as the negative logarithm to the base 10, of the molar concentration of OH− ions in solution.
pOH = -log10[OH-]
pH scale is a scale for measuring the hydrogen ion concentration in a solution.
Define pH.
The pH of a solution is defined as the negative logarithm to the base 10, of the concentration of H+ ions in solution in mol dm–3.
pH is expressed mathematically as
pH = -log10 [H+] or pH = -log10 [H3O+]
Salt is a compound formed by the partial or total replacement of the ionisable hydrogen atoms of an acid by a metallic ion or an ammonium ion.
Define the following term:
Efflorescence
It is the phenomenon by which hydrated salts, on exposure to dry air, lose their water of crystallization and crumble to powder.
Define the following term:
Hygroscopy
It is the phenomenon by which substances absorb moisture from air, but only sufficiently so as to become wet.
Formulae [1]
Write a balanced equation for the preparation of the following salt:
Zinc carbonate from zinc sulphate.
\[\ce{ZnSO4 + (NH4)2CO3 -> (NH4)2SO4 + ZnCO3}\]
Key Points
pH = negative logarithm of H₃O⁺ ion concentration (mol/L).
- The pH scale (0–14) measures the concentration of H⁺ ions in a solution; values < 7 indicate acids, > 7 indicate bases, and 7 is neutral.
- A universal indicator shows different colours at different pH levels, helping to determine the strength of an acid or base.
- Strong acids/bases produce more H⁺ or OH⁻ ions in solution, while weak acids/bases produce fewer ions at the same concentration.
| S.No. | Area of Life | Role of pH |
|---|---|---|
| 1. | Human Body | Functions within pH range 7.0 – 7.8; imbalance can affect survival. |
| 2. | Agriculture |
Crops grow best in a specific pH:
|
| 3. | Acid Rain | Rainwater with pH < 5.6 contains acids (H₂SO₄, HNO₃, H₂CO₃) from pollutants; these harm soil, marine life, and monuments. |
| 4. | Medicine | Diseases are diagnosed by checking blood and urine pH. |
| 5. | Digestive System | Excess HCl lowers pH, causing pain; antacids like Mg(OH)₂ neutralise it. |
| 6. | Tooth Decay | pH < 5.5 corrodes tooth enamel; toothpaste neutralizes mouth acids. |
| 7. | Bee Sting | Injects acid into the skin; baking soda (a base) neutralises the sting. |
Important Questions [15]
- Answer the Following Question. Identify the Acid and the Base from Which Sodium Chloride is Obtained. Which Type of Salt is It? When is It Called Rock Salt? How is Rock Salt Formed?
- A metal 'M' on reacting with dilute acid liberates a gas 'G'. The same metal also liberates gas 'G' when reacts with a base. Write the name of gas 'G'. How will you test the presence of this gas?
- Out of Hcl and Ch3cooh, Which One is a Weak Acid and Why? Describe an Activity to Support Your Answer.
- Out of Three Metals P, Q and R, P is Less Reactive than Q and R is More Reactive than P and Q Both. Suggest an Activity to Arragne P, Q and R in Order of Their Decreasing Reactivity.
- One of the events that does not occur during photosynthesis is ______.
- A small amount of copper oxide was taken in a beaker and dilute hydrochloric acid was added with continuous stirring of the solution. Name the compound formed and state the colour of its solution.
- An aqueous solution of a salt turns blue litmus to red. The salt could be the one obtained by the reaction of ______.
- You Are Asked to Prepare Hard Water in Your Laboratory. Select a Group from the Following Groups of Salts, Any Salt of Which You May Dissolve in Distilled Water to Obtain Hard Water.
- Hard Water Required for an Experiment is Not Available in a School Laboratory. However, Following Salts Are Available in the Laboratory.
- Name the salt formed when sulphuric acid is added to sodium hydroxide and write its pH.
- The Ph of a Salt Used to Make Tasty and Crispy Pakoras is 14. Identify the Salt and Write a Chemical Equation for Its Formation. List Its Two Uses.
- How is bleaching powder prepared? Write a chemical equation of the reaction involved in the preparation of bleaching powder.
- Assertion (A): Reaction of Quicklime with water is an exothermic reaction. Reason (R): Quicklime reacts vigorously with water releasing a large amount of heat.
- The chemical formula for plaster of Paris is:
- A compound which is prepared from gypsum has the property of hardening when mixed with water. identify the compound and write its formula. How is this compound prepared?
Concepts [24]
- Introduction to Acids, Bases and Indicators
- Indicators for Testing Acids and Bases
- Acids
- Properties of Acids
- Common Properties of Acids
- Uses of Acids
- Bases
- Properties of Bases
- Uses of Bases
- Chemical Properties of Acids and Bases
- Common Properties of Acids and Bases
- Strength of Acid and Base Solutions : pH Scale
- Universal Indicator
- Importance of pH in Everyday Life
- Salts
- Salts > Family of Salts
- Salts > pH of Salts
- Common Salt
- Sodium hydroxide
- Washing Soda
- Baking Soda
- Bleaching Powder
- Plaster of Paris
- Water of Crystallisation: Hydrated Salts
