Section outline

    • Give reasons for the following:
      Q1. Why great care should be taken while handling laboratory acids and bases?

      Ans:

      Care should be taken while handling laboratory acids and bases because:

      1. They are corrosive in nature.
      2. Hence, they can irritate and harm the skin.
      Q2. Why are historical buildings, monuments are getting yellowish?

      Ans:

      1. Historical buildings, monuments are getting yellowish due to acid rains.
      2. Air contains carbon dioxide, sulphur dioxide and nitrogen dioxide which are released as pollutants.
      3. During the rainy season, these pollutants dissolve in rain drops to form carbonic acid, sulphuric acid and nitric acid respectively.
      4. This rain which contains excessive of acids is called acid rain and it corrodes the historical buildings & monuments damaging them.
      Q3. What is the nature of tooth paste and why?

      Ans:

      1. The tooth paste is basic in nature.
      2. The bacteria in the mouth breakdown the leftover food and release acids.
      3. These acids can cause tooth decay and bad breath in the mouth.
      4. Hence, to neutralize these acids the toothpaste is basic in nature.
      Q4. My grandmother prepared some lemon pickle. I stored it in two different containers made of steel & glass. After some days, the pickle in one of the containers got spoiled. Why? Name the acids present in the pickle.

      Ans:

      1. The lemon pickle contains citric acid & acetic acid (vinegar which is the preservative).
      2. Acids are corrosive in nature.
      3. They react with metals and corrode them leading to change in taste & colour of the pickle which is hazardous for our health.
      4. Thus the pickle in steel container which is made up of metal will get spoilt while that in glass container will remain good.

       

    • Answer the following questions in short:
      Q1. Why do we use indicators?

      Ans:

      1. Indicators change color based on the acidity or basicity of a solution.
      2. Thus, they help us to identify the nature of the solution.
      Q2. What are the different indicators?

      Ans:

      Different indicators are litmus paper, turmeric paper, China rose indicator, red cabbage, phenolphthalein & methyl orange.

      Q3. What happens when an acid reacts with a metal?

      Ans:

      • When an acid reacts with a metal, it produces hydrogen gas and a salt.
      • For example, when hydrochloric acid reacts with zinc, it forms zinc chloride and releases hydrogen gas.
      Q4. How do acids and bases affect the color of turmeric paper?

      Ans:

      Turmeric paper is an indicator which changes color as below:

      1. With acid no change that is it remains yellow.
      2. With base it changes to red.
      Q5. What happens to in purple cabbage juice in acid & base solutions?

      Ans:

      • The purple cabbage juice changes to red in acidic solution.
      • And it changes to yellow in basic solution.

       

    • Answer the following questions:
      Q1. How to prepare China rose indicator & what is the change in colour for different solutions?

      Ans:

      1. Collect and place some red coloured China rose petals in a beaker.
      2. Add some warm water to it.
      3. After some time, the water will become red coloured & indicator is ready.
      4. Add few drops of indicator to different solutions.
      5. The indicator will turn dark pink (magenta) in acidic solutions.
      6. It will turn green in basic solutions.
      7. There will be no change in neutral solutions.