Download App

Science Answer the questions.[Che-2M]

Acids, Bases and Salts · CBSE STD 10 (CBSE - English Medium). 106 questions.

Questions · Page 1 of 3

Answer the questions.[Che-2M]

🎯

Test yourself on this topic

50 questions · timed · auto-graded

Question 12 Marks
Why do acids not show acidic behaviour in the absence of water?
Answer
Acids produce hydrogen ions or hydronium ions only in presence of water. Therefore, it shows acidic behavior only presence of water.
View full question & answer→
Question 22 Marks
Why does distilled water not conduct electricity, whereas rain water does?
Answer
Distilled water cannot conduct electricity because it does not contain ions while rain water conducts electricity as it contains ions due presence of dissolved salts in it.
View full question & answer→
Question 32 Marks
Give two important uses of washing soda (or sodium carbonate).
Answer
  1. It is used as cleansing agent for domestic purposes.
  2. It is used for removing permanent hardness of water.
View full question & answer→
Question 42 Marks
What is a neutralisation reaction? Give two examples.
Answer
The reaction between an acid and a base to give salt and water is called neutralization reaction.
For example:
NaOH + HCl → NaCl + H2O
KOH + HNO3 → KNO3 + H2O
View full question & answer→
Question 52 Marks
Plaster of Paris should be stored in a moisture-proof container. Explain why?
Answer
The Plaster of Paris should be stored in a moisture-proof container as it absorbs water from moisture and turn into hard substance (Gypsum) as shown in following chemical equation.

$\text{CaSO}_4.\frac{1}{2}\text{H}_2\text{O}+1\frac{1}{2}\text{H}_2\text{O}\xrightarrow{\text{Heat}}\text{CaSO}_4.2\text{H}_2\text{O}\$\text{Plaster of Paris})(\text{Water})\ \ \ \ \ \ \ \ \ \ \ \ (\text{Gypsum})\ \ \ \ $

View full question & answer→
Question 62 Marks
A milkman adds a very small amount of baking soda to fresh milk.
  1. Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
  2. Why does this milk take a long time to set as curd?
Answer
  1. Milk is made slightly alkaline so that it may not become sour easily due to the formation of lactic acid in it.
  2. The alkaline milk takes a longer time to set into curd because the lactic acid being formed has to first neutralise the alkali present in it.
View full question & answer→
Question 72 Marks
Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.
Answer
Bacteria change the fresh milk into curd by producing lactic acid. Because of the presence of lactic acid in curd, the pH will come down from 6 to lower value.
View full question & answer→
Question 82 Marks
Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH3COOH) is added to test tube B. In which test tube will the fizzing occur more vigorously and why?
Answer
The fizzing will occur strongly in test tube A, in which hydrochloric acid (HCl) is added. This is because HCl is a stronger acid than CH3COOH and therefore produces hydrogen gas at a faster speed due to which fizzing occurs.
View full question & answer→
Question 92 Marks
  1. Name the products formed when sodium hydrogen carbonate is heated.
  2. Write the chemical equation for the reaction involved in the above.
Answer

  1. On heating sodium hydrogen carbonate (NaHCO3), it decomposes to form sodium carbonate (Na2CO3), water (H2O) and carbon dioxide (CO2).

  2. $2 NaHCO _3(s) \xrightarrow {\text { (Heat) }} \underset{\substack{\text { Sodium carbonate } \\ \text { (Soda ash) }}}{Na _2 CO _3(s)}+ CO _2( l )+ H _2 O ( g )$
View full question & answer→
Question 102 Marks
Write the chemical formula for washing soda. How may it be obtained from baking soda? Name an industrial use of washing soda other than washing clothes.
Answer
Chemical formula for washing soda: $\text{Na}_{2}\text{ CO}_{3}.10\text{ H}_{2}\text{O}$

It may be obtained on heating, baking soda produces sodium carbonate

$\text{2 NaHCO}_{3}\xrightarrow{\Delta} \text{Na}_{2} \text{CO}_{3} + \text{H}_{2}\text{O + CO}_{2.}$

Recrystallization of sodium carbonate gives washing soda.

$\text{Na}_{2} \text{CO}_{3} + \text{10H}_{2}\text{O}\rightarrow\text {Na}_{2} \text{CO}_{3.} \text{10H}_{2}\text {O.}$

Uses:-

washing soda is used in making glass, soap and paper industries.

View full question & answer→
Question 112 Marks
  1. If you are asked to report your observations about the following two properties of acetic acid, what would you report?
  1. Odour.
  2. Effect on litmus.
  1. If you take a pinch of sodium hydrogen carbonate powder in a test-tube and add drop-by-drop acetic acid to it, what would you observe immediately? List any two main observations.
Answer
  1.  
  1. Smells like vinegar.
  2. Turns blue litmus red.
  1.  
  1. Brisk effervescence.
  2. Evolution of colourless gas.
View full question & answer→
Question 122 Marks
A student is studying the properties of acetic acid in his school laboratory. List two physical and two chemical properties which he must observe and note in his record book.
Answer
Physical properties−
  1. Smell like vinegar.
  2. Colourless liquid.
Chemical propertirs−
  1. Turns blue litmus red.
  2. Gives brisk effervescence with sodium carbonate.
View full question & answer→
Question 132 Marks
A gas is liberated immediately with a brisk effervescence, when you add acetic acid to sodium hydrogen carbonate powder in a test tube. Name the gas and describe the test that confirms the identity of the gas.
Answer
When acetic acid (CH3COOH) is added to the sodium hydrogen carbonate (NaHCO3) than carbon dioxide gas produce with brisk effervescence.
CH3COOH + NaHCO3 → CH3COONa + CO2↑ + H2O
Observations: The gas turns lime water milky that confirms the identity of CO2 gas.
Ca(OH)2 + CO2 → CaCO3↓ + H2O
View full question & answer→
Question 142 Marks
What is ‘Baking Powder’? How does it make the cake soft and spongy?
Answer
Baking powder is a mixture of baking soda (NaHCO3) and an edible acid like tartaric acid. Baking powder on heating produces carbon dioxide gas which causes bread or cake to rise making it soft and spongy.
View full question & answer→
Question 152 Marks
A compound ‘X’ on heating with excess conc. sulphuric acid at 443K gives an unsaturated compound ‘Y’. ‘X’ also reacts with sodium metal to evolve a colourless gas ‘Z’. Identify ‘X’, ‘Y’ and ‘Z’. Write the equation of the chemical reaction of formation of ‘Y’ and also write the role of sulphuric acid in the reaction.
Answer
X is ethanol.

Y is ethene.

Z is hydrogen gas.

When ethanol is heated with excess amount of concentrated sulphuric acid, it gives an unsaturated compound ethene (C2H4). Conc. H2SO4 acts as a dehydrating agent because it ejects water from ethanol.

Reaction:

$\text{CH}_3\text{CH}_2\text{OH}\xrightarrow{\text{Conc.H}_2\text{So}_4}\text{CH}_2=\text{CH}_2+\text{H}_2\text{O}$

Now, when ethanol reacts with sodium, a colourless gas is evolved, which is hydrogen gas.

Reaction:

$2\text{CH}_3\text{CH}_2\text{OH}+2\text{Na}\xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ }2\text{CH}_3\text{CH}_2\text{ONa}+\text{H}_2$

View full question & answer→
Question 162 Marks
What is observed when 2mL of dilute hydrochloric acid is added to 1g of sodium carbonate taken in a clean and dry test tube? Write chemical equation for the reaction involved.
Answer
On adding dilute hydrochloric acid to sodium carbonate taken in a clean and dry test tube, a brisk effervescence will be observed due to the evolution of carbon dioxide gas.

$2\text{HCl}+\text{Na}_2\text{CO}_3\xrightarrow{\ \ \ \ \ \ \ }2\text{NaCl}+\text{H}_2\text{O}+\text{CO}_2$

View full question & answer→
Question 172 Marks
In the experimental set up to show that "CO2 is given out during respiration", name the substance taken in the small test tube kept in the conical flask. State its function and the consequence of its use.
Answer
In the above mentioned experimental setup, lime water is taken in a small test tube which is kept in the conical flask. Lime water is used to detect the presence of carbon dioxide.
When carbon dioxide passes through lime water, it turns milky due to the formation of calcium carbonate.
Hence, it is used in the above experiment to check whether CO2 is released during respiration.
View full question & answer→
Question 182 Marks
Blue litmus solution is added to two test tubes A and B containing dilute HCl and NaOH solution respectively. In which test tube a colour change will be observed? State the colour change and give its reason.
Answer
Test tube A contains dil. HCl and test tube B contains dil. NaOH. On adding blue litmus solution to both the test tubes, the colour of the test tube A will change from blue to red. This is because HCl is an acid and acids turn blue litmus to red.
View full question & answer→
Question 192 Marks
You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic?
Answer
A pH value of less than 7 indicates an acidic solution, while greater than 7 indicates a basic solution. Therefore, the solution with pH = 6 is acidic and has more hydrogen ion concentration than the solution of pH = 8 which is basic.
View full question & answer→
Question 202 Marks
You have been provided with three test-tubes. One of these test-tubes contains distilled water and the other two contain an acidic and a basic solution respectively. If you are given only blue litmus paper, how will you identify the contents of each test-tube?
Answer
Acidic solution will turn blue litmus red; This red litmus will turn blue in basic solution; Distilled water will have no effect on any type of litmus pape,
View full question & answer→
Question 212 Marks
You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?
Answer
The contents of each test tube would be identified by change in colour of red litmus paper. For example, when we wet the red litmus paper with the basic solution, it changes into blue colour. Put the changed blue litmus paper in the solution which turns the blue to red will be the acidic solution. The solution, which has no effect on any litmus paper, will be neutral and hence it will be distilled water.
View full question & answer→
Question 222 Marks
You are given three solutions A, B and C with pH values 2, 10 and 13 respectively. Write which solution has more hydrogen ions concentration among the three and state the nature ‘acidic or basic’ of each solution.
Answer
A has maximum [H+] concentration A is acidic. B and C are basic in nature.
View full question & answer→
Question 232 Marks
Write the role of HCl present in the stomach.
Answer
Hydrochloric acid gets mixed with food and kills the bacteria present in food. It also destroys the structure of proteins so that the enzymes can digest them easily. Hydrochloric acid also creates acidic conditions necessary for the action of the enzyme pepsin. It activates pepsin to act on proteins.
View full question & answer→
Question 242 Marks
Write the neutralisation reaction between acids and bases in terms of the ions involved.
Answer
$\text{H}^+\text{(aq)}\ \ +\ \ \text{OH}^-\text{aq}\xrightarrow[\text{Reaction}]{\text{Neutralisation}}\text{H}_2\text{O}(\text{l})\\^{\text{Hydrogenions}}\ \ \ ^\text{Hydroxideions}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^{\text{Whater}}\\^{\text{(From acid)}}\ \ \ \ \ \ ^{\text{(From bases)}}$
View full question & answer→
Question 252 Marks
Write the balanced chemical equation of chloro-alkali process.
Answer

  1. $\text{NaOH}\ +\ \text{HNO}_3\xrightarrow{\ \ \ \ \ \ \ \ \ \ }\text{NaNO}_3\ +\ \text{H}_2\text{O}$ (Salt name- Sodium nitrate)

  2. $2\text{KOH}\ +\ \text{H}_2\text{SO}_4\xrightarrow{\ \ \ \ \ \ \ \ \ \ }\text{K}_2\text{SO}_4\ +\ 2\text{H}_2\text{O}$ (Salt name-Potassium sulphate)

View full question & answer→
Question 262 Marks
Write an equation to show the reaction between Plaster of Paris and water.
Answer
Plaster of Paris has a very remarkable property of setting into a hard mass on wetting with water. So, when water is added to plaster of Paris, it sets into a hard mass in about half an hour. The setting of plaster of Paris is due to the hydration crystals of gypsum, which set to form a hard, solid mass.
View full question & answer→
Question 272 Marks
Why should curd and sour substances not be kept in brass and copper vessels?
Answer
Curd and other sour substances contain acids. Therefore, when they are kept in brass and copper vessels, the metal reacts with the acid to liberate hydrogen gas and harmful products, thereby spoiling the food.
View full question & answer→
Question 282 Marks
Why should curd and other sour foodstuffs (like lemon juice, etc.) not be kept in metal containers (such as copper and brass vessels)?
Answer
Curd and other sour substances contains acids which can react with the metals of brass and copper vessels to form toxic (poisonous) metal compounds which can cause food poisoning and damage our health.
View full question & answer→
Question 292 Marks
Why is the electrolysis of a concentrated solution of sodium chloride known as chlor-alkali process?
Answer
The electrolysis of a concentrated solution of sodium chloride known as chlor-alkali process because of the products formed:
  1. The products formed in this reaction are NaOH (a strong base/alkali), chlorine and hydrogen gas.
  2. “Chlor” means chlorine and “alkali” means base i.e. NaOH.
View full question & answer→
Question 302 Marks
Why do HCl, H2SO4, HNO3, etc., show acidic character in aqueous solutions while solutions of compounds like C6H12O6 (glucose) and C6H12OH (alcohol) do not show acidic character?
Answer
The acidic character of a substance is due to the presence of hydrogen ions [H+(aq) ions] in its aqueous solution. HCl, H2SO4 etc show acidic properties because they produce hydrogen ions when dissolved in water. The solution of compounds like alcohol and glucose do not show acidic character because they do not ionize in water to produce hydrogen ions or any other ions in solution.
View full question & answer→
Question 312 Marks
Why do HCl, HNO3, etc. show acidic characters in aqueous solutions while solutions while solutions of compounds like alcohol and glucose do not show acidic character?
Answer
HCl and HNO3 etc. dissociate in presence of water to form hydrogen ions (H+). These hydrogen ions combine with H2O to form hydronium ions (H3O+).

The reaction can be given as follows:

$\text{HCl}\xrightarrow{\ \ \ \ \ \ }\text{H}^+\ +\ \text{Cl}^-$

$\text{H}^+\ +\ \text{H}_2\text{O}\xrightarrow{\ \ \ \ \ \ }\text{H}_3\text{O}^+$

Because of this property HCl and HNO3 show acidic character in aqueous solutions. On the other hand, alcohol and glucose cannot dissociate in water to form hydrogen ions. Hence, they do not show acidic character.

View full question & answer→
Question 322 Marks
Why do HCl, HNO3, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?
Answer
When HCl or HNO3 are mixed with water then they dissolve in water to form H+ or H3O+ ions which shows their acidic character.
For example just see the following reactions:
HCl (aq) → H+ + Cl-
H+ + H2O → H3O+
When alcohols and glucose are mixed with water then they do not dissolve to form ions. Hence they do not show acidic character.
View full question & answer→
Question 332 Marks
Why does dry HCl gas not change the colour of the dry litmus paper?
Answer
Dry HCl gas does not contain any hydrogen ions in it, so it does not show acidic behaviour. In fact, dry HCl gas does not change the colour of dry litmus paper as it has no hydrogen ions [H+(aq) ions] in it.
View full question & answer→
Question 342 Marks
While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
Answer
Since the process of dissolving an acid in water is exothermic, it is always recommended that acid should be added to water. If it is done the other way, then it is possible that because of the large amount of heat generated, the mixture splashes out and causes burns.
View full question & answer→
Question 352 Marks
Which type of chemical compound found in citrus fruits?
Answer
Citrus fruits contain an acid called citric acid. Lemon, orange are examples of citrus fruits. They also contain ascorbic acid which is commonly known as Vitamin C. In short, the chemical compound found in citrus fruits is acidic in nature.
View full question & answer→
Question 362 Marks
Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?
Answer
Usually hydrogen gas is liberated when an acid reacts with a metal.
For example:
Zn + 2HCl → ZnCl2 + H2
When a burning candle or matchstick is bought near hydrogen gas it burns with pop sound.
View full question & answer→
Question 372 Marks
Which gas is liberated when dilute hydrochloric acid reacts with sodium carbonate? How will you test for the presence of this gas?
Answer
CO2 gas is liberated during the reaction. When carbon dioxide gas formed in the form of brisk effervescence is passed through lime water, it turns the lime water milky. If excess of carbon dioxide gas is passed through the milky lime water, the solution becomes clear again. This confirms the presence of carbon dioxide gas.
View full question & answer→
Question 382 Marks
Which chemical is injected into the skin of a person:
During the nettle leaf hair sting?
How can the effect of these stings be neutralised?
Answer
Methanoic acid. The effect of methanoic acid can be neutralised by rubbing a mild base like baking soda solution on the stung area of the skin.
View full question & answer→
Question 392 Marks
Which acid is produced in our stomach? What happens if there is an excess of acid in the stomach? How can its effect be cured?
Answer
Our stomach produces hydrochloric acid. If there is excess of hydrochloric acid in the stomach, it causes indigestion which produces pain and irritation. Its effect can be cured by taking antacids.
View full question & answer→
Question 402 Marks
When the concentrated aqueous solution of substance X is electrolysed, then NaOH, Cl2 and H2 are produced. Name the substance X. What is the special name of this process?
Answer
Substance X, which gives sodium hydroxide, Cl2 and H2 upon electrolysis, is NaCl. The electrolysis of sodium chloride solution is called the chlor-alkali process because of the products formed, 'chlor' for chlorine and 'alkali' for sodium hydroxide (NaOH).
View full question & answer→
Question 412 Marks
When a solution is added to vanilla extract, then the characteristic smell of vanilla cannot be detected. State whether the given solution is an acid or a base.
Answer
When Hydrochloric acid reacts with an active metal (like zinc), we observe that gas filled bubbles are formed on the surface of the metal. Pass the gas formed through soap solution. Then, bring a burning candle near the gas filled soap bubble. If the gas present in bubble burns with a ‘pop’ sound, then its hydrogen gas.
View full question & answer→
Question 422 Marks
When a solution becomes more acidic, pH gets lower.
Answer
Acids are those chemical substances which have a sour taste.
Example: Acetic acid and citric acid.
Base is a chemical substance which has a bitter taste.
Example: Caustic soda and washing soda.
View full question & answer→
Question 432 Marks
What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.
Answer
Sodium hydrogen carbonate solution on heating gives sodium carbonate, carbon dioxide and water.

$2\text{NaHCO}_3+\text{heat}\ \ \rightarrow\ \ \text{Na}_2\text{CO}_3+\text{CO}_2+\text{H}_2\text{O}$

View full question & answer→
Question 442 Marks
What will be the action of the following substances on litmus paper? Dry HCl gas, Moistened NH3 gas, Lemon juice, Carbonated soft drink, Curd, Soap solution.
Answer
Dry HCl gas will not have any effect on litmus paper. Moistened NH3 gas will turn red litmus blue. Curd, lemon juice, carbonated soft drink will turn blue litmus red. Soap solution will turn red litmus blue.
View full question & answer→
Question 452 Marks
What is meant by strong acids and weak acids? Classify the following into strong acids and weak acids:
HCl, CH3 COOH, H2SO4, HNO3, H2CO, H2SO3
Answer
A strong acid is one that completely ionises in water to form a large amount of hydrogen ions whereas a weak acid only partially ionises in water and thus produces a small amount of hydrogen ions.
HCl, H SO, HNO are strong acids; CH COOH, H CO, H SO are weak acids.
View full question & answer→
Question 462 Marks
What is gypsum? What happens when gypsum is heated to 100°C (373 K)?
Answer
Gypsum is calcium sulphate dihydrate, CaSO.2H O. When gypsum is heated to a temperature of 100?C, it loses 3/4th of its water of crystallisation and forms plaster of Paris.
View full question & answer→
Question 472 Marks
What is bleaching powder? How is bleaching powder prepared? Write chemical equation of the reaction involved in the preparation of bleaching powder.
Answer
Bleaching powder is Calcium oxychloride (CaOCl ). It is prepared by passing chlorine gas over dry slaked lime.

$\text{Ca(OH)}_2+\text{Cl}_2\rightarrow\text{CaOCl}_2+\text{H}_2\text{O}$

View full question & answer→
Question 482 Marks
What is a universal indicator? For what purpose is it used?
Answer
Universal indicator is a mixture of many different indicators which gives different colours at different pH values of the entire pH scale. It is used to obtain an idea of how acidic or basic a substance is.
View full question & answer→
Question 492 Marks
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
A salt is a compound formed from an acid by the replacement of the hydrogen in the acid by a metal.
Example: Sodium chloride – NaCl; It is obtained from hydrochloric acid and sodium metal. Ammonium chloride – NH Cl; It is obtained from ammonia and hydrochloric acid.
View full question & answer→
Question 502 Marks
What is an olfactory indicator? Name two olfactory indicators. What is the effect of adding sodium hydroxide solution to these olfactory indicators?
Answer
Those substances whose smell (or odour) changes in acidic or basic solutions are called olfactory indicators. Onion and vanilla extracts are olfactory indicators. When a basic solution like sodium hydroxide solution is added to a cloth strip treated with onions (or onion extract), then the onion smell cannot be detected.
View full question & answer→
Generate Paper FreeAll Acids, Bases and Salts topics