(National Book Foundation - New Book/New Syllabus Based on National Curriculum Pakistan 2024-2025 and Onwards)
(Class 8 General Science Notes for 8th Centralized Exam 2024-2025 and onward, FDE, Islamabad)
(Class 8 General Science Notes for 8th Centralized Exam 2024-2025 and onward, FDE, Islamabad)
Click Here for Solved MCQs Unit-7
D. Structured questions
1. In an experiment, a student is adding hydrochloric acid to sodium hydroxide solution, until the pH of the mixture changes to 7.
a) How can
he find out if the pH of the mixture changed to 7?
Ans: We can find out by
neutralization reaction if the pH of the mixture changes to 7.
b) Is the
mixture acidic, alkaline, or neutral when pH is 7?
Ans: The mixture is
neutral when pH is 7.
c) What
products are present in the beaker, when pH changes to 7?
Ans: NaCl and H₂O are present in
beaker, when pH changes to 7.
d) What
will happen to the pH, if more or excess hydrochloric acids is added?
Ans: It will lower the pH
value.
2. A chemical reaction is occurring between two substances in a beaker.
Temperature changes from 25°C to 50°C in the beaker and pH changes to 7.
a) Is the
reaction exothermic? Explain your answer.
Ans: As the temperature
increases, so it is exothermic.
b) What
type of chemical reaction has occurred in the beaker?
Ans: A neutralization
reaction has occurred in a beaker.
c) What
type of reactants are present in the beaker?
Ans: A neutralization
reaction has occurred in a beaker.
d) What
could be the final products in the reaction?
Ans: Salt and water could
be the final products in the reaction.
E. Project
work
Search and prepare report about the acids used in jams, jellies, tomato
ketchup, pickles and toilet cleaners.
Ans: The acids commonly used in jams, jellies, tomato ketchup, pickles, and toilet cleaners are :
1. Jams
and Jellies:
Citric Acid:
Widely utilized as a natural preservative and flavor enhancer in jams and
jellies. It helps to regulate acidity, prevent spoilage, and impart a tart
taste to the fruit mixture.
2. Tomato Ketchup:
Acetic
Acid (Vinegar): A
primary ingredient in tomato ketchup, providing tanginess and acting as a
preservative. Vinegar helps to maintain product freshness and inhibits
microbial growth.
3. Pickles:
Acetic Acid (Vinegar): Essential for
pickling vegetables, acetic acid imparts sourness and serves as a preservative
by creating an acidic environment that prevents bacterial growth and spoilage.
Lactic Acid: Produced during the
fermentation process in some pickles, lactic acid contributes to flavor
development and preservation.
4. Toilet Cleaners:
Hydrochloric
Acid (HCl):
Commonly found in toilet bowl cleaners, hydrochloric acid effectively dissolves
mineral deposits, stains, and organic matter. It helps to sanitize and remove
tough buildup from toilet surfaces.
Sulfamic
Acid:
Another acid used in toilet cleaners, sulfamic acid aids in removing limescale
and organic stains while disinfecting and deodorizing toilet bowls.
These acids play
crucial roles in their respective products, whether it's enhancing flavor,
preserving freshness, or aiding in cleaning and disinfection. Manufacturers
carefully formulate their products to ensure effectiveness while adhering to
safety standards and regulations. Consumers should be aware of these
ingredients and follow proper usage instructions for optimal results and
safety.
Class 8 General Science Notes (Main Page)
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