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