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Chapter No.-2 Acids Bases and Salts Hots
(High Order Thinking skill)
Que1: Kazi and priyam want to prepare dil H2SO4 .Kazi added conc.H2SO4 to water slowly with constant stirring& cooling whereas Priyam added water to conc. H2SO4.Name the student who was correct and why?
Ans.1 Kazi was correct. If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns. The glass container may also break due to excessive local heating.
Que2: Compound P forms enamel of teeth. It is the hardest substance of the body. It does not dissolve in water but it is corroded when pH in the mouth is below 5.5. How does tooth paste prevent dental decay?
Ans.2 P = Ca3 (PO4)2. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating. Using toothpastes, which are generally basic, for cleaning the teeth can neutralize the excess acid and prevent tooth decay.
Que3: The oxide of a metal M was water soluble when a blue litmus strip was dipped in this solution, itmdid not go any change in colour. Predict the nature of oxide
Ans.3 The Metal oxide (MO) is of basic in nature. It dissolves in water to form metal hydroxide as MO + H2O -> M (OH) 2 B lue litmus does not undergo any change in colour in the basic medium.
Que4: A first aid manual suggests that vinegar should be used to treat wasp sting and baking soda for bee stings.
(i) What does this information tell you about the chemical nature of the wasp stings
(ii) If there were no baking soda in the house, what other household substance could you use to treat bee stings?
Ans 4: (i) Since vinegar (acetic acid) is used to heal or neutralize the effect of wasp stings this means that the chemical present in the stings must be some base.
Que5: A road tanker carrying an acid was involved in an accident and its contents spilled on the road. At the side of the road, ron drain covers began melting and fizzing as the acid ran over them. A specialist was called to see if the acid actually leaked into the nearby river.
(a) Explain how the specialist could carry out a simple test to see if the river water contains some acid or not.
(b) The word melting is incorrectly used in the report. Suggest a better name that should have been used.
(c) Explain why drain covers began fizzing as the acid rain over them.
Ans : (a) By dipping a strip of blue litmus paper in to the sample of river water. If the colour changes to red this means that some acid has gone in to the river.
(c) Iron reacts with acid to evolve hydrogen gas.
Que6: A few drops of phenolphthalein indicator were added to an unknown solution A. It acquired pink colour. Now another unknown solution B was added to it drop by drop and the solution becomes colorless. Predict the nature of A & B.
Ans. 6: Sol `A` is basic in nature as phenolphthalein has imparted pink colour to it. Sol `B` is an acid it has made solution A colourless by neutralizing by its basic effect.
Que7: A student heated a few crystals of copper sulphate in a dry boiling tube.
a) What will be the color of the copper sulphate after heating?
(b) Will you notice water droplets in the boiling tube?
c) Where have these come from?
Ans7 : (a) White (b) Yes (c) Copper sulphate crystals which seem to be dry contain water of crystallization.
8 A substance `X` used in the kitchen for making tasty crispy pakoras.and is also an ingredient of antacid. Name the substance `X`.
(i) How does `X` help to make cakes and bread soft and spongy.
(ii) Is the pH value of solution of `X` is lesser than or greater than 7.0?
Ans 8 ( i) When CO2 gas escapes as bubbles it leaves behind pores which make the cake or bread soft and spongy.
(ii) It is a salt of strong base so the pH of the solution will be more than 7.0
Que 9: After drinking access of cold drink, a person suffered from acidity. Explain?
Ans9: Cold drink contains carbon dioxide dissolved in them under pressure. Some amount of the gas escapes when a bottle of cold drink is opened while a portion of it remain dissolved. Carbon dioxidemdissolved in water forms a weak acid, carbonic acid. Consumption of excess of cold drink accumulation of carbonic acid in the stomach which is responsible for the development of acidity.
Que10: Although acetic acid is highly soluble in water but still it is a weak acid. Explain why?
Ans: The strength of an acid depends upon the extent of ionization. Acetic acid is highly soluble in water but it dissociates partially in the aqueous solution to produce a small amount of H+ ions and , therefore, considered as a weak acid.
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