COMPRE SCI 3 ADV
UNIT 3 LESSON 7
Acids, bases and salts
1. Which of the following properties is a chemical property?
ANSWER: flammability
2. Which of the following substances is a compound?
ANSWER: water (H2O)
3. Which of the following substances is an element?
ANSWER: hydrogen
4. Which of these properties is a chemical property?
ANSWER: flammability
5. The chemical formula for methane is CH4. What is the fixed ratio of carbon (C) to hydrogen (H)?
ANSWER: 1:4
6. Which of the following is a characteristic of acidic solutions?
ANSWER: Sour taste
7. Which of the following is a characteristic of basic solutions?
ANSWER: Slippery feel
8. A salt is formed when a(n) _________ reacts with a(n) _________.
ANSWER: acid; base
9. In the reaction HCl + NaOH -> NaCl + H2O, what is the role of HCl?
ANSWER: Acid
10. What is the role of NaOH in the reaction HCl + NaOH -> NaCl + H2O?
ANSWER: Base
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6. Define an acid.
ANSWER: An acid is a substance that typically donates hydrogen ions (H+) in a chemical reaction, and has a pH value less than 7.
7. Provide an example of a common acid.
ANSWER: Vinegar (acetic acid), lemon juice (citric acid), and stomach acid (hydrochloric acid) are common examples of acids.
8. Define a base.
ANSWER: A base is a substance that typically accepts hydrogen ions (H+) in a chemical reaction or donates hydroxide ions (OH-), and has a pH value greater than 7.
9. Provide an example of a common base.
ANSWER: Sodium hydroxide (NaOH), baking soda (sodium bicarbonate), and ammonia (NH3) are common examples of bases.
10. What are salts?
ANSWER: Salts are ionic compounds formed when a base reacts with an acid, resulting in the replacement of the hydrogen ion from the acid with a metal ion from the base.
11. How are salts formed?
ANSWER: Salts are formed through a chemical reaction between an acid and a base, called neutralization reaction. The hydrogen ion (H+) from the acid combines with the hydroxide ion (OH-) from the base to form water (H2O), while the remaining ions combine to form the salt.
12. Provide an example of a common salt.
ANSWER: Sodium chloride (NaCl), also known as table salt, is a common example of a salt. Other examples include calcium carbonate (CaCO3) and potassium nitrate (KNO3).
13. What is the pH scale?
ANSWER: The pH scale is a measure of the acidity or alkalinity (basicity) of a substance. It ranges from 0 to 14, with values below 7 indicating acidity, 7 indicating neutrality, and values above 7 indicating alkalinity.
14. How is the pH of a substance determined?
ANSWER: The pH of a substance is determined by measuring the concentration of hydrogen ions (H+) in the solution. A pH meter or pH indicator strips can be used to measure and determine the pH level.
15. What is the relationship between acids and bases on the pH scale?
ANSWER: Acids have pH values less than 7, closer to 0, indicating acidity. Bases have pH values greater than 7, closer to 14, indicating alkalinity. The closer the pH value is to 7, the more neutral the substance is.
16. What is meant by the term "neutralization reaction"?
ANSWER: Neutralization reaction refers to a chemical reaction between an acid and a base, where the acidic and basic properties are neutralized, resulting in the formation of water and a salt.
17. Explain the concept of pH indicators.
ANSWER: pH indicators are substances that change color in response to different pH levels. They are used to visually determine the approximate pH of a substance based on the color change observed.
18. Give an example of a pH indicator.
ANSWER: Litmus paper, phenolphthalein, bromothymol blue, and universal indicator solution are examples of pH indicators.
19. How does an acid-base indicator work?
ANSWER: An acid-base indicator works by changing its color depending on the concentration of hydrogen ions in the solution. In acidic conditions, certain indicators change to one color, while in basic conditions they change to a different color, allowing for a visual determination of the pH level.
20. What is the concept of "strong" and "weak" acids/bases?
ANSWER: "Strong" acids or bases are substances that ionize or dissociate completely in water, releasing a high concentration of hydrogen ions (H+) or hydroxide ions (OH-). "Weak" acids or bases only partially ionize or dissociate, resulting in a lower concentration of hydrogen or hydroxide ions.
To answer these questions, we need to understand the concepts of chemical properties, compounds, elements, and chemical formulas.
1. A chemical property refers to a characteristic or behavior of a substance that can only be observed during a chemical reaction or chemical change. Flammability is an example of a chemical property because it describes how a substance reacts with oxygen to produce heat and light. To identify a chemical property, you would look for characteristics related to chemical reactions or changes.
2. A compound is a substance composed of two or more elements chemically bonded together in a fixed ratio. Water (H2O) is an example of a compound because it is composed of two hydrogen atoms bonded to one oxygen atom. To identify a compound, you would look for a combination of elements in a fixed ratio.
3. An element is a pure substance composed of only one type of atom. Hydrogen is an example of an element because it consists of only hydrogen atoms. To identify an element, you would look for a single type of atom.
4. As mentioned earlier, flammability is a chemical property. It describes the ability of a substance to burn or ignite when exposed to oxygen. This property is typically observed during a chemical reaction. To identify a chemical property, you would look for characteristics related to chemical reactions or changes.
5. The chemical formula for methane is CH4. In this formula, the ratio of carbon (C) to hydrogen (H) can be determined. There is one carbon atom (C) and four hydrogen atoms (H), so the fixed ratio of carbon to hydrogen in methane is 1:4.