NCERT Questions (Page 18 )
Q.1
You have been provided with three test tubes. One of them contains distilled water and the other two contains an acidic and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tubes?
Ans.
Red litmus paper becomes blue when comes in contact with Basic solution. So dip red litmus in test tubes to find which one has basic solution. If it turns blue when dipped into Test tube 1 then test tube 1 has basic solution, if it does not change its colour, dip into another test tube. In this way we can find which test tube has basic solution.
Now, dip the blue litmus in both the remaining test tubes. That test tube which changes blue litmus into red litmus has Acidic solution. That test tube which does not change colour has distilled water.
NCERT Questions page 22)
Q.1
Why should curd and sour substances not be kept in brass and copper vessels?
Ans.
Sour substances loke pickles, curd etc. are acidic in nature. They are highly reactive to brass and copper metals.
If we keep curd and sour substances in brass and copper vessels, a chemical reaction starts taking place between the sour substance and the metal which in turn form toxic materials dangerous for our body.
Q2.
Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the pressure of this gas?
Ans.
Hydrogen gas is liberated when an acid reacts with a metal.
for example
Zn + 2HCl > ZnCl2 + H2
When Zinc reacts with hydrochloric acid, it forms zinc chloride and liberates hydrogen.
Test for Hydrogen
Hydrogen gas is insoluble in water. So, when soap solution is mixed with hydrogen. Hydrogen does not mix with the solution instead starts making bubbles. These bubbles ultimately makes a blast.
Q.3
Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compound formed is calcium chloride.
Ans.
The compound formed is calcium chloride and the fire extinguisher is CO2.
The reaction goes like this
CaCO3 + 2HCl > CaCl2 + CO2 + H2O
That is,
When Calcium Carbonate reacts with hydrochloric acid, it forms Calcium chloride and liberate carbon dioxide and water.
(NCERT Q./Ans Page 28)
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Q1. You have two solutions A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic?
Answer
Since Solution A has more hydrogen ions, so A is more acidic. Solution B is basic.
Q2.
What affect does the concentration of H+ ions have the nature of the solution?
Answer
The solution which have more H+ ions is more acidic in nature.
Q3.
Do basic solutions have H+ ions? If yes, then why are these basic?
Answer
Basic solutions do have H+ ions. But these solutions have H- ions more than H+ ions. As these solutions have excess amount of H-ions, they are basic in nature.
Q4.
Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime( calcium hydroxide) or chalk ( calcium carbonate)?
Answer
The ideal pH scale range of soil to grow plants is 6 to 8. So if the soil is more acidic, a farmer treats the soil with bases like quick lime/ slacked lime/ chalk so as to maintain its pH scale.
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