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Learning Objectives
1. Knowledge and Understanding
Define Acids, Bases, and Salts: Understand the basic definitions of acids, bases, and salts, and how they differ chemically.
Identify Properties of Acids and Bases:
Acids: Know characteristics such as sour taste, reactivity with metals, and pH less than 7.
Bases: Know characteristics such as bitter taste, slippery feel, and pH greater than 7.
Understanding Indicators: Learn about indicators (e.g., litmus paper, phenolphthalein) and their role in identifying acids and bases.
pH Scale: Recognize the pH scale as a measure of acidity or alkalinity, where 7 is neutral, below 7 is acidic, and above 7 is basic.
2. Application and Identification
Classify Common Substances: Classify everyday items (like lemon juice, soap, vinegar, baking soda) as acidic, basic, or neutral based on their properties.
Recognize Neutralization: Understand the concept of neutralization as a reaction between an acid and a base to produce salt and water.
3. Experimentation and Observation
Use Indicators: Conduct simple experiments using indicators to identify acids and bases, such as testing with litmus paper or natural indicators like turmeric and cabbage juice.
Observe Neutralization Reactions: Perform experiments to observe neutralization, such as mixing vinegar (acid) with baking soda (base) and identifying the products.
4. Real-World Connections and Applications
Importance of Acids, Bases, and Salts in Daily Life:
Understand the uses of common acids (e.g., vinegar in cooking, citric acid in citrus fruits).
Recognize the uses of bases (e.g., baking soda in cooking, soap for cleaning).
Identify the role of salts in food preservation, medicine, and industry.
Environmental Impact: Understand how acids and bases affect the environment, such as acid rain's impact on soil and water sources.
5. Safety and Precautions
Handle Acids and Bases Safely: Learn and apply safety measures when handling acids and bases, especially in a lab setting, like wearing gloves and goggles.
Disposal: Recognize the importance of proper disposal of acidic and basic substances to prevent environmental harm.
6. Critical Thinking and Analysis
Predict and Analyze Outcomes: Make predictions about what happens when acids and bases are mixed, and analyze results from simple experiments.
Interpret Data: Observe and interpret changes in indicators or pH levels during experiments, and draw conclusions based on evidence.
1.1 Knowledge and Understanding: Acids, Bases, and Salts
Definitions of Acids, Bases, and Salts
Definitions of Acids, Bases, and Salts
Acids: Acids are substances that release hydrogen ions (H⁺) when dissolved in water. They have a sour taste, can conduct electricity, and react with metals to produce hydrogen gas. Acids turn blue litmus paper red. Examples include hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and vinegar (acetic acid, CH₃COOH).
Bases: Bases are substances that release hydroxide ions (OH⁻) when dissolved in water. They have a bitter taste, feel slippery, and can conduct electricity. Bases turn red litmus paper blue. Examples include sodium hydroxide (NaOH), potassium hydroxide (KOH), and baking soda (sodium bicarbonate, NaHCO₃).
Salts: Salts are ionic compounds formed from the neutralization reaction between an acid and a base. They consist of positive and negative ions but do not release H⁺ or OH⁻ ions in solution, so they are usually neutral (pH 7). Common examples include table salt (sodium chloride, NaCl) and calcium carbonate (CaCO₃).
Chemical Differences
Chemical Differences
Acids produce H⁺ ions in solution, which makes them acidic.
Bases produce OH⁻ ions in solution, which makes them basic (alkaline).
Salts are formed by the combination of the positive ion from a base and the negative ion from an acid, creating a neutral compound.
Properties of Acids and Bases
Properties of Acids and Bases
Acids:
Taste: Acids typically have a sour taste (like lemon juice or vinegar).
Reactivity: Acids react with metals (e.g., zinc, magnesium) to produce hydrogen gas.
Conductivity: Acids conduct electricity because they release hydrogen ions (H⁺) in solution.
pH Level: Acids have a pH of less than 7, with stronger acids having lower pH values.
Effect on Indicators: Acids turn blue litmus paper red.
Bases:
Taste: Bases generally have a bitter taste (like baking soda).
Feel: Bases feel slippery or soapy to the touch (like soap or cleaning products).
Conductivity: Bases conduct electricity because they release hydroxide ions (OH⁻) in solution.
pH Level: Bases have a pH greater than 7, with stronger bases having higher pH values.
Effect on Indicators: Bases turn red litmus paper blue.
Understanding Indicators
Understanding Indicators
Indicators are substances that change color in the presence of an acid or a base, helping to identify their nature. Common indicators include:
Litmus Paper:
Red Litmus: Turns blue in a basic solution.
Blue Litmus: Turns red in an acidic solution.
Phenolphthalein:
Colorless in acidic or neutral solutions.
Turns pink in basic solutions.
Natural Indicators:
Turmeric: Turns red in basic solutions (e.g., soap solution) but stays yellow in acidic solutions.
Red Cabbage Juice: Changes color depending on the pH of the solution, from red in acids to green/yellow in bases.
The pH Scale
The pH Scale
The pH scale is a scale from 0 to 14 that measures the acidity or alkalinity of a solution:
Neutral (pH 7): Pure water is neutral, with a pH of 7.
Acidic (pH < 7): Solutions with pH values less than 7 are acidic; the lower the pH, the stronger the acid.
Basic/Alkaline (pH > 7): Solutions with pH values greater than 7 are basic; the higher the pH, the stronger the base.
The pH scale is logarithmic, meaning each unit change represents a tenfold change in hydrogen ion concentration, which helps to compare the strength of acids and bases.
Properties of Acids:
Acids change the colour of litmus from blue to red.
They convert the colour of Methyl Orange from Orange/Yellow to Pink.
Acids turn the pink colour of Phenolphthalein to colourless.
Acids can conduct electricity.
Some Acids are highly corrosive in nature which means that they corrode or rust metals.
Acids tend to evolve hydrogen gas whilst reacting with an active metal such as Zn, Mg, etc.
They produce H+ ions when mixed with water.
Acids lose their acidity when mixed with a base.
When equal amounts of acid and base are combined the process of neutralization occurs and salt and water is formed,
The pH value of acid is from 0-6. Learn the concept of pH value here.
Acids are sour in taste.
Acids react with carbonates and hydrogen carbonates to form a salt, water, and carbon dioxide gas.
Extremely active metals such as Potassium (K), Calcium (Ca), Sodium (Na), etc tend to explode when combined with acids.
Weak Acids like Carbonic Acid doesn’t act with any metal at all.
Nitric Acids doesn’t usually exhibit acidic properties, it exhibits oxidizing properties instead.
Metals that generally react with dilute acid to form salt and hydrogen are the metals which lie above hydrogen in the metal activity series.
Acids form a salt, water and sulphur dioxide while reacting with sulphites and bisulphites.
Acids and metal sulphides form salt and hydrogen sulphide.
They are classified on the basis of their sources, strength, concentration, the presence of oxygen and its basicity.
The different types of acids are organic acids, mineral acids, strong acids, weak acids, concentrated acids, dilute acids, Oxy-acids, Hydracids, monobasic acids, dibasic acids, and tribasic acids.
ASSESMENT 1.1
Multiple Choice Questions
Which of the following is a property of acids?
a) Bitter taste
b) Slippery feel
c) Sour taste
d) Turns red litmus paper blue
Which property is common to all bases?
a) Sour taste
b) Slippery feel
c) Turns blue litmus paper red
d) Reacts with metals to produce hydrogen gas
What color does blue litmus paper turn in an acidic solution?
a) Red
b) Blue
c) Green
d) No color change
A solution has a pH of 9. This solution is:
a) Acidic
b) Neutral
c) Basic
d) Strongly acidic
What is the purpose of using indicators in testing substances?
a) To change the pH of the solution
b) To identify if the substance is an acid or a base
c) To make the solution taste better
d) To neutralize the solution
True or False
Acids have a pH level greater than 7.
Phenolphthalein turns pink in a basic solution.
Bases typically have a bitter taste and a pH less than 7.
Neutral solutions have a pH of exactly 7.
A substance that turns red litmus paper blue is likely a base.
Fill in the Blanks
An acid usually has a __________ taste and a pH __________ than 7.
A base feels __________ to the touch and has a pH __________ than 7.
A pH of 7 indicates a __________ solution.
__________ is a natural indicator that can change color to identify acids and bases.
When added to an acidic solution, blue litmus paper will turn __________.
Short Answer
Name one common household acid and one common household base.
What color does phenolphthalein turn in a basic solution?
Why is the pH scale useful in determining the nature of a solution?
If a solution has a bitter taste and turns red litmus paper blue, what can you infer about the solution?
Explain why acids can react with metals to produce hydrogen gas.
1. Answer: c) Sour tast
2. Answer: b) Slippery feel
3. Answer: a) Red
4. Answer: c) Basic
5. Answer: b) To identify if the substance is an acid or a base
6. Answer: False
7. Answer: True
8. Answer: False
9. Answer: True
10. Answer: True
11. Answer: sour, less
12. Answer: slippery, greater
13. Answer: neutral
14. Answer: Litmus (or Red Cabbage Juice, depending on context
15. Answer: red
16. Answer: Acid: Vinegar (acetic acid); Base: Baking soda (sodium bicarbonate)
17. Answer: Pink
18. Answer: The pH scale helps determine if a solution is acidic, neutral, or basic, based on its pH value.
19. Answer: The solution is likely a base.
20. Answer: Acids release hydrogen ions (H⁺) in solution, which can react with metals to form hydrogen gas and a salt.
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