Chemistry
A teacher showed a chemistry experiment in the class to her students. She poured about 100 ml of sodium hydroxide into a beaker and added a few drops of phenolphthalein to it. The colour of the solution immediately changed. Then she added dilute sulphuric acid to the beaker slowly, while constantly stirring the solution with a glass rod. She kept on adding dilute sulphuric acid until the solution became colourless again. Then she called her students to touch the beaker.
(a) Name the type of reaction which involves an acid and a base as shown by the teacher.
(b) What colour change was observed when phenolphthalein was added to the beaker?
(c) Write a balanced chemical equation for the reaction between sodium hydroxide and dilute sulphuric acid.
(d) What will the students feel on touching the beaker after the reaction? Why?
(e) Why do many toothpastes contain bases?
(f) Name:
(i) a basic substance to treat an acidic soil.
(ii) an acidic substance to treat a basic soil.
Answer
(a) The type of reaction which involves an acid and a base as shown by the teacher is neutralisation reaction.
(b) Phenolphthalein turns pink in a basic solution. When acid is added, the solution becomes colourless.
(c) A balanced chemical equation for the reaction between sodium hydroxide and dilute sulphuric acid is :
2NaOH + H2SO4 ⟶ Na2SO4 + 2H2O
(d) On touching the beaker after the reaction, the students will feel the beaker warm because neutralisation is an exothermic reaction that releases heat.
(e) Many toothpastes contain bases because bases neutralise the acids produced by bacteria in the mouth. This helps to prevent tooth decay.
(f) (i) Quicklime is a basic substance used to treat acidic soil.
(ii) Organic matter or sulphate salts may be used to treat basic soil.
Related Questions
How will you obtain?
(a) Magnesium oxide from magnesium.
(b) Silver chloride from silver nitrate.
(c) Nitrogen dioxide from lead nitrate.
(d) Zinc chloride from zinc.
(e) Ammonia from nitrogen.
Also give balanced equations for the reactions.
(a) What is meant by metal activity series?
(b) A metal P was placed in a solution of silver nitrate. After sometime, silver was deposited on metal P and the solution turned blue.
(i) Which is more reactive - metal P or silver?
(ii) What kind of reaction is this?
(iii) Give an example of this type of reaction.
Following is a list of metals :
Na, Zn, Fe, Ag, Pb, Hg, Cu.
Answer the questions that follow :
(a) Which of the above metals can displace all the metals from their salt solution ?
(b) Name one of the above metals which cannot react with dilute acid to produce hydrogen gas.
(c) Name one of the above metals which reacts with oxygen upon heating to produce an amphoteric oxide.
(d) Arrange the above metals in a decreasing order of their reactivity.
Given below is a diagram showing a type of reaction between two compounds. Answer the questions that follow :
(a) What compound is X ?
(b) Give a balanced chemical equation to form X.
(c) Name the type of reaction shown.