Midterm Chemistry Quiz for Class 7
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Questions and Answers

What color does methyl orange indicator turn in an acidic solution?

  • Blue
  • Red (correct)
  • Colorless
  • Yellow

    • Which of the following is a natural indicator?

  • Phenolphthalein
  • Methyl orange
  • Litmus (correct)
  • All of the above

    • What is the pH of pure water?

  • 1
  • 0
  • 14
  • 7 (correct)

    • What type of salt is formed when a strong acid reacts with a strong base?

    <p>Neutral (C)</p> Signup and view all the answers

    What color does red cabbage extract turn in a basic (alkali) solution?

    <p>Yellow (A)</p> Signup and view all the answers

    If a solution turns blue litmus paper red, what kind of solution is it?

    <p>Acidic (C)</p> Signup and view all the answers

    What color would you most likely see when using a strong base in a pH measuring?

    <p>Dark blue or Violet (C)</p> Signup and view all the answers

    What are the two components of lichen?

    <p>Fungi and algae (D)</p> Signup and view all the answers

    Which type of salt is formed from the reaction of a strong acid and a weak base?

    <p>Acidic salt (D)</p> Signup and view all the answers

    What is a common substance used by ants for defense, behaving like a base?

    <p>Baking soda (B)</p> Signup and view all the answers

    Which of the following processes is not involved in the anaerobic decomposition of sludge in a wastewater treatment plant?

    <p>Aerobic bacteria break down the sludge. (C)</p> Signup and view all the answers

    Why might plants grow poorly in soil that is not closer to a pH of 7?

    <p>Because acidic or alkaline soil conditions impede their ability to uptake necessary nutrients (C)</p> Signup and view all the answers

    What is the approximate percentage of freshwater available on Earth compared to the total water?

    <p>3% (A)</p> Signup and view all the answers

    Which of the following is the largest source of freshwater on Earth?

    <p>Icecaps and Glaciers (B)</p> Signup and view all the answers

    What is the primary purpose of the skimmer in a wastewater treatment plant?

    <p>To remove floating grease and oil (D)</p> Signup and view all the answers

    What is the key characteristic of bases in terms of taste and touch?

    <p>Bitter in taste and soapy to the touch (D)</p> Signup and view all the answers

    What is the primary difference that distinguishes a physical change from a chemical change?

    <p>Physical changes do not result in new substances being formed, while chemical changes do (A)</p> Signup and view all the answers

    How is the water removed from the activated sludge in a wastewater treatment plant?

    <p>The water is removed using sand drying beds or machines. (A)</p> Signup and view all the answers

    What is the process called where water seeps into the ground and replenishes groundwater?

    <p>Infiltration (D)</p> Signup and view all the answers

    What is the role of chlorine in wastewater treatment?

    <p>To kill harmful bacteria (C)</p> Signup and view all the answers

    What is the term used to describe the top level of the groundwater layer?

    <p>Water table (B)</p> Signup and view all the answers

    Which of the following best represents a synthetic indicator of acids and bases?

    <p>Phenolphthalein (D)</p> Signup and view all the answers

    Which of the following processes would be classified as a physical change?

    <p>Boiling of water (B)</p> Signup and view all the answers

    Which of these is NOT a major factor contributing to the depletion of the water table?

    <p>Water harvesting (D)</p> Signup and view all the answers

    Why is the dried sludge from a wastewater treatment plant considered valuable?

    <p>It can be used as fertilizer for plants. (C)</p> Signup and view all the answers

    Which of the following is a water management technique aimed at minimizing water usage in gardens?

    <p>Drip irrigation (A)</p> Signup and view all the answers

    If a substance turns red litmus paper blue, what does this indicate about the substance?

    <p>It is basic (D)</p> Signup and view all the answers

    What is the purpose of pumping air into the clarified water in a wastewater treatment plant?

    <p>To encourage the growth of aerobic bacteria that consume remaining waste (A)</p> Signup and view all the answers

    Which of the following best describes the purpose of bar screens in a wastewater treatment plant?

    <p>To remove large objects like plastic bags (C)</p> Signup and view all the answers

    What is the process in the water cycle where water turns into clouds?

    <p>Condensation (B)</p> Signup and view all the answers

    Which of these options represents the largest proportion of surface water?

    <p>Lakes (C)</p> Signup and view all the answers

    Which of the following is most likely to be a direct source of wastewater?

    <p>A hospital (D)</p> Signup and view all the answers

    When lime water reacts with carbon dioxide, what observable change typically occurs?

    <p>The solution takes on a milky appearance. (C)</p> Signup and view all the answers

    What is the color of copper metal?

    <p>Reddish brown (A)</p> Signup and view all the answers

    In the reaction where iron is added to copper sulphate solution, what color change is observed in the solution?

    <p>From blue to green (B)</p> Signup and view all the answers

    Which of the following correctly represents the word equation for the reaction between copper sulphate and iron?

    <p>Copper sulphate + Iron → Iron sulphate + Copper (D)</p> Signup and view all the answers

    Which of the following is NOT typically associated with a chemical change?

    <p>A change in texture (A)</p> Signup and view all the answers

    What process is used to deposit a layer of zinc on iron to prevent rusting?

    <p>Galvanization (A)</p> Signup and view all the answers

    Which of the following best describes a physical change?

    <p>It only changes the physical properties of a substance. (B)</p> Signup and view all the answers

    When iron rusts, what is the primary substance that forms on its surface?

    <p>Iron oxide (C)</p> Signup and view all the answers

    Which of the following substances is known to contain weak natural acids?

    <p>Orange juice (A)</p> Signup and view all the answers

    What is the primary reason strong acids are considered dangerous to consume?

    <p>They can cause severe harm even when diluted (A)</p> Signup and view all the answers

    What should be done when diluting an acid?

    <p>Always add acid to water (A)</p> Signup and view all the answers

    Which of the following acids is not classified as a mineral acid?

    <p>Carbonic acid (C)</p> Signup and view all the answers

    What is the effect of acids on blue litmus paper?

    <p>It turns red (A)</p> Signup and view all the answers

    Which of the following is an example of a weak edible acid?

    <p>Citric acid (C)</p> Signup and view all the answers

    Which property of acids allows them to conduct electricity?

    <p>They dissociate into ions in solution (C)</p> Signup and view all the answers

    What role does baking soda play in the stomach when someone overeats?

    <p>It neutralizes excess hydrochloric acid (C)</p> Signup and view all the answers

    Study Notes

    Midterm Marathon for Class 7th Chemistry

    • The study session is a marathon for Class 7th Chemistry, presented by Ananaya Ma'am.

    Today's Goals

    • Acids, Bases and Salts
    • Physical and Chemical Changes
    • Water Waste Story
    • Water: A Precious Resource

    Chapter No. - 01: Acids, Bases and Salts

    • Acids and Bases
      • Examples of acids include orange juice, lemon juice, tamarind, and vinegar.
      • Examples of bases include baking soda, milk of magnesia, and soap.
      • Acids taste sour.
      • Bases taste bitter.
      • Acids turn blue litmus paper red.
      • Bases turn red litmus paper blue.
    • Acids
      • Sour taste
      • Chemical nature of acids is acidic
      • Latin word acere meaning sour
      • Natural acids
      • Mineral acids:
        • Prepared from minerals
        • Man-made acids
        • Strong acids
        • Examples: Hydrochloric (HCl), sulfuric (H₂SO₄), nitric (HNO₃) acids
        • Weak acids
          • Examples: Citric acid, acetic acid
          • Edibles
      • Strong vs Weak Acids
        • Strong acids are very dangerous
        • Dilute solutions of strong acids are harmful
        • Carbonic acid is used in fizzy drinks and water
      • Diluting Acids
        • Always add acid to water and never the reverse
    • Bases
      • Bitter taste
      • Soapy to touch
      • Electrolyte
      • Neutralize acids
      • Examples include sodium hydroxide (NaOH), potassium hydroxide (KOH).
      • Types of bases:Alkalis
      • Alkalis
        • Dissolve in water
        • Example of Alkalis include sodium hydroxide (NaOH).
      • Properties of Bases
        • Bases turn red litmus to blue
        • Bases conduct electricity
      • Uses of Bases:
        • Neutralizing excess stomach acid
        • Baking soda, also called sodium hydrogen carbonate, is an antacid.
    • Salts
      • Formed by the reaction of acids and bases
      • Neutral
      • Example: Sodium chloride (NaCl)

    Chapter No. - 02: Physical and Chemical Changes

    • Physical Changes
      • Change in physical properties: size, shape, color, state
      • Reversible change
      • No new substance is formed
    • Chemical Changes
      • Formation of one or more new substances
      • Usually involves a chemical reaction
      • Example: Rusting of iron, burning of magnesium ribbon, burning a candle, melting of wax

    Chapter No. - 03: Waste Water Story

    • What is Sewage?
      • Wastewater from homes, industries.
      • Rainwater that washes off streets and rooftops.
      • Impurities are dissolved or suspended in the water
      • Liquid waste
      • Contains solid waste, liquid, and gasses
    • Wastewater Treatment Plant (WWTP)
      • Physical, chemical, and biological processes remove contaminants
      • Bar screens remove large objects (rags, sticks, cans, etc)
      • Grit and pebbles settle down
      • Water is allowed to settle in a large tank, to separate solids
      • Sludge (solid waste) is removed
      • Skimmer removes floating solids like oil, grease.
      • Water is clarified
      • Sludge is transferred to tanks for the anaerobic bacteria to decompose it
      • Biogas produced in the process can be used as fuel or to generate electricity
      • Activated sludge and water are removed from top
      • Aerobic bacteria help consume waste
    • Water Management
      • Rainwater can be used to recharge groundwater.
      • Drip irrigation, is a technique of watering plants by making use of narrow tubing's, which deliver water directly to the base of the plant

    Chapter No. - 04: Water: A Precious Resource

    • World Water Day: Celebrated March 22
    • Available Water:
      • 97% is salt water, 3% is fresh water
        • Of the 3%, 68.7% is in Icecaps and Glaciers, .3% is Surface water
      • Of the 3% fresh water, 2% is rivers, 87% are lakes, 30.1% in groundwater and .9% other
    • Water Cycle:
      • Evaporation, Transpiration, Condensation, Precipitation
    • Groundwater:
      • Water in aquifers (layers of hard rock)
      • Recharged by infiltration
      • Can be pumped out using wells or hand pumps
    • Depletion of Water Table
      • Increasing population and industries lead to depletion
      • Leads to increased consumption in daily activities
      • Agriculture,watering crops
    • Water Management:
      • Rainwater harvesting
      • Drip irrigation (watering plants directly at the base)

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    Chemistry Midterm Syllabus Class 7th PDF

    Description

    This quiz covers essential topics in Class 7 Chemistry, focusing on Acids, Bases, and Salts, along with Physical and Chemical Changes. Engage with various concepts, including the properties of acids and bases and the significance of water as a resource.

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