Q1: Write chemical equation for the reaction of zinc metal on sodium hydroxide.
Answer: Zn(s) + 2NaOH(aq) -> Na2ZnO2 (aq) + H2 (g)
Q2: Three acidic solutions A, B and C have pH = 0, 3 and 5 respectively.
a. Which solution has the highest concentration of H+ ions?
b. Which solution has the lowest concentration of H+ ions?
Answer: a. The solution with pH = 0 has highest concentration of H+ ions.
b. The solution with pH = 5 has lowest concentration of H+ ions.
Q3: What is meant by p and H in pH?
Answer: p stands for ‘potenz’ in German meaning power, H stands of hydrogen.
Q4: Define alkalies and give an example.
Answer: Water soluble bases are called alkalies e.g., NaOH.
Q5: Mention the range of pH for identification of a base.
Answer: 7.1 to 14 is the pH range for bases.
Q6: How chloride of lime differs from calcium chloride?
Answer: CaOCl2 is the chloride of lime whereas CaCl2 calcium chloride.
Q7: What is meant by water of crystallisation in a substance?
Answer: The water molecules associated with a crystalline solid are called water of crystallisation.
Q8: Write the chemical name and chemical formula of washing soda.
Answer: Na2 CO3.10H2O, sodium carbonate deca-hydrate is washing soda.
Q9: What effect does an increase in concentrationH+(aq) ions in a solution have on pH of solution?
Answer: Increase in H+ concentration will lead to decrease in pH.
Q10: Name a gas evolved when dilute HCl reacts with sodium hydrogen carbonate. How is it recognised?
Answer: Carbon dioxide, it turns lime water milky. In this way, CO2 gas is recognised.
Q11: What are olfactory indicators?
Answer: Those indicators whose smell changes in acidic and basic solutions.
Q12: Why does 1 M HCl solution have a high concentration of H+ ions than 1 M CH3 COOH solution?
Answer: It is because 1M HCl is a strong acid and it is completely ionised in aqueous solution whereas CH3 COOH is a weak acid, so it is only partially ionised.
Q13: Write the chemical equation representing the action of atmospheric CO2 gas on bleaching powder when left exposed in open.
Answer: CaOCl2 + CO2 -> CaCO3 + Cl2
Q14: How will you test for the gas which is liberated when hydrochloric acid reacts with an active metal?
Answer: Bring a burning matchstick near the gas. If it is burnt with ‘pop’ sound, the gas is H2.
Q15: How is the pH of solution of an acid influenced when it is diluted?
Answer: pH of the solution increases when it is diluted.
Q16: At what pH rain water is said to be acidic ?
Answer: When pH < 5.5, the rain water becomes acidic.
Q17: Which gas is evolved when dilute hydrochloric acid reacts with zinc metal? Write the molecular formula of this gas.
Answer: Dihydrogen gas, H2
Q18: Dry HCl gas does not change the colour of dry blue litmus. Give reason to justify it.
Answer: Dry HCl (g) does not form ions, therefore it does not affect dry blue litmus.
Q19: Why is HCl a stronger acid than acetic acid?
Answer: HCl is completely ionised in aqueous solution whereas acetic acid is only partially ionised in aqueous solution.
Q20: Name the chemicals used in acid fire extinguisher and the gas evolved from it when it is used?
Answer: NaHCO3 (Sodium hydrogen carbonate) and H2SO4 (Sulphuric acid). The gas evolved is carbon dioxide.
Q21: Which is a stronger acid, with pH = 5 or with pH=2?
Answer: The acid with pH = 2 is a stronger acid.
Q22: A compound which is prepared from gypsum has the property of hardening when mixed with a proper quantity of water. Identify the compound and write its chemical formula.
Answer: CaSO4. 21 H2O (Plaster of Paris), Calcium sulphate hemihydrate.
Q23: What is meant by term pH of solution? The pH of rain water collected from two cities A’ and ‘B’ were found to be 6.0 and 5.0 respectively. The water of which city will be more acidic?
Answer: pH of solution is defined as negative logarithm of H+ ion concentration. It determines the strength of acid and base. Rainwater with pH = 5 is more acidic.
Q24: A few drops of sulphuric acid are added to water before electrolysis, why?
Answer: Water is not a good conductor of electricity. Few drops of sulphuric acid makes it better conductor of electricity.
Q25: Write the names of two salts belonging to sodium family.
Answer: NaCl, Na2CO3 are two salts belonging to sodium family.
Q26: Which among distilled water, tap water and sea water is the best conductor of electricity?
Answer: Sea water is a better conductor due to the presence of ions.
Q27: Name the acids present in (i) nettle sting, (ti) curd.
Answer: (i) HCOOH, Formic acid,
(ii) Lactic acid, CH3-CH(OH)-COOH
Q28: Name a salt which does not contain water of crystallisation.
Answer: NaHCO3 is a salt that does not contain water of crystallisation.
Q29: Write the name and chemical formula of the product formed by heating gypsum at 373 K.
Answer: Plaster of Paris, CaSO4. 21 H2O
Q30: The pH of a sample of vegetable soup was found to be 6.5. How is this soup likely to taste?
Answer: It will be sour in taste.
Q31: Which bases are called alkalies? Give one example of alkali.
Answer: Those bases which are soluble in water are called alkalies e.g., NaOH, KOH.
Q32: Write the name and chemical formula of the product formed by action of chlorine on slaked lime.
Answer: CaOCl2, Bleaching powder, Calcium oxy-chloride.
Q33: Write a balanced chemical equation for the reaction between sodium carbonate and hydrochloric acid indicating the physical state of reactants and the products.
Answer: Na2CO3(s) + 2HCl(aq) → 2NaCl(aq) + CO2(g) + H2O(l)
Q34: Name the acid and base that have constituted the salt ammonium nitrate.
Answer: Acid: HNO3, Base: NH4OH (i.e., Nitric acid, Ammonium hydroxide).
Q35: Suggest one way to reduce alkaline nature of the soil.
Answer: Add ammonium nitrate (Acidic salt) to neutralise alkaline nature of soil.
Q36: Name two synthetic indicators which is used for acid and base test.
Answer: Methyl orange and phenolphthalein to test for acids and bases.
Q37: What are the examples of olfactory indicator?
Answer: Vanilla, Onion and Clove are the examples of olfactory indicator.
Q38: What is the chemical name of bleaching powder?
Answer: The chemical name of bleaching powder is calcium oxychloride (CaOCl2).
Q39: What are the materials used for the preparation of bleaching powder?
Answer: The materials used for the preparation of bleaching powder are slaked lime Ca(OH)2, and chlorine gas Cl2.
Q39: State two use of bleaching powder?
Answer: It is used for disinfecting drinking water supply, and in textile industry as bleaching agent.
Q40: What is baking soda?
Answer: Baking soda is a compound made up of brine, carbon dioxide, and ammonia.
Q41: What is chemical equation of baking soda?
Answer: The chemical equation of baking soda is:
NaCl + H2O + CO2 + NH4 -> NaHCO3 + NH4Cl
Q42: What are the usage of baking soda?
Answer: The usage of baking soda are:
i) Reduce the acidity in stomach.
ii) Acts as antacid which is used to treat stomach upset and indigestion.
iii) Used in the process of washing as a water softener.
Q43: What is the gas evolved when baking soda is heated?
Answer: When the baking soda is heated, carbon dioxide gas is evolved.
Q44: What is the chemical name of baking soda?
Answer: The chemical name of baking soda is sodium bicarbonate (NaHCO3).
Q45: What is the chemical name of washing soda?
Answer: The chemical name of washing soda is sodium carbonate (Na2CO3).
Q46: What is soda ash?
Answer: The soda ash is known as sodium carbonate (Na2CO3).
Q47: Name a metal compound which has detergent properties?
Answer: sodium carbonate (Na2CO3).
Q48: Name a sodium compound used for making borax and glass?
Answer: sodium carbonate (Na2CO3).
Q49: How many water molecules are present in washing soda?
Answer: 10 molecules
Q50: Which process is used for making washing soda?
Answer: Solvay's process.
Q51: How can washing soda be obtained from baking soda? Name an industrial use of washing soda other than washing clothes.
Answer: On heating the baking soda strongly, we can obtain washing soda.Sodium bicarbonate on heating gives sodium carbonate, carbon dioxide and water. It is largely used in the manufacturing of paper, glass, rayon, etc
