Q. When a piece of limestone reacts with dilute HCl, a gas X is produced. When gas X is passed through lime water then a white precipitate Y is formed. On passing excess of gas X, the white precipitate dissolves forming a soluble compound Z.
- What are X, Y and Z ?
- Write equations for the reactions which take place :
- when limestone reacts with dilute HCl
- when gas X reacts with lime water to form white precipitate Y
- when excess of gas X dissolves white precipitate Y to form a soluble compound
- X is carbon dioxide; Y is calcium carbonate; Z is calcium hydrogen carbonate
Q. If someone is suffering from the problem of acidity after overeating, which of the following would you suggest as remedy ? Lemon juice, Vinegar, Baking soda solution Give reason for your choice.
- ANSWER– In such condition we use Baking Soda because it is a basic salt.
- This basic salt will neutralize the excess of acidity and provide relief to the person.
Q.What would you expect the pH of pure water to be ?
What colour would the universal indicator show in an aqueous solution of sugar ? Why
A sample of rain water turned universal indicator paper yellow. What would you expect its pH to be ? Is it a strong or a weak acid ?
- ANSWER– The pH of pure water is 7.
- the sugar solution is neutral in nature hence universal indicator show green colour.
- the sample of rain water turned universal indicator paper yellow, this shows that is a weak acid.
Q. What is a salt ? Give the names and formulae of any two salts. Also name the acids and bases from which these salts may be obtained.
- ANSWER– salt is a chemical compound which is formed by the reaction of an
acid with a base.
- sodium chloride salt ( NaCl) it is prepared by reaction between sodium hydroxide base and hydrochloric acid .
- potassium chloride (KCl) it is prepared by reaction between potassium hydroxide base and hydrochloric acid .
Q. What is meant by ‘a family of salts’ ? Explain with examples.
- ANSWER – when salts are prepared by reaction between same acids or same bases,
they are classified as a family.
- example- sodium chloride and potassium chloride are salts that belong to the
chloride family because of the chloride radicals in them.
Q. What is meant by ‘hydrated’ and ‘anhydrous’ salts ? Explain with examples.
- ANSWER – A chemical compound which have one or more chemically bonded water molecule in the structure lattice of compound are known as hydrated salts
Example: Copper sulphate pentahydrate (CuSO4.5H2O)
- Anhydrous salt: A chemical compound in which all water molecules are removed from main strucutre lattice of compound is called Anhydrous salt.
- example : copper sulphate pentahydrate convert into copper sulphate on heating
Q. Write the names, formulae and colours of any two hydrated salts?
- ANSWER -copper sulfate pentahydrate – CuSO4.5H2O – blue in colour
Cobalt chloride – CoCl. 6H2O – Pink
Q. What will be the colour of litmus in an aqueous solution of ammonium chloride salt ?
- ANSWER – aqueous solution of ammonium chloride salt is acidic in nature.
- red litmus paper show no colour change and it turn a blue litmus paper to red