How is pH measured and why is it important?

pH is measured by pH paper or meters; important for testing acidity/basicity in the lab, environment, and industry.

What are the characteristics of salts used in everyday life?

Salts can be neutral, acidic or basic; have varied uses like seasoning food, water softening, or as chemicals in labs.

Why is copper sulphate used to show water of crystallization?

It is blue when hydrated (CuSO4·5H2O) and turns white when anhydrous, making the water visible in a lab demonstration.

What pH value indicates a neutral solution and give an example.

pH = 7 is neutral; pure water is a neutral solution.

How does baking powder help bakery products rise?

Baking powder releases carbon dioxide when heated, making cakes and bread soft and spongy.

Name two indicators and their color changes in acids and bases.

Litmus: red in acid, blue in base; Methyl orange: red in acid, yellow in base.

What are the effects of acidic and basic solutions on the skin?

Acids can sting or burn, bases can feel soapy but may cause irritation if concentrated. Both can damage tissue on prolonged contact.

Explain the reaction of acids with metal carbonates.

Acid + metal carbonate forms salt, water, and carbon dioxide gas.

What are the main products of the chlor-alkali process?

Sodium hydroxide, chlorine gas, and hydrogen gas are produced from brine electrolysis.

What is the significance of pH in everyday life?

pH controls processes like digestion, tooth health, plant growth, and industrial chemical reactions.

Why should acids never be added to water all at once?

Adding acid to water slowly with stirring prevents rapid, dangerous heat release and splashing.

Give two examples of naturally occurring acids and their sources.

Citric acid in lemons and lactic acid in curd and sour milk.

What happens when carbon dioxide is passed through lime water?

Lime water turns milky due to the formation of insoluble calcium carbonate.

Why do acids liberate hydrogen gas with some metals?

Acids react with reactive metals displacing hydrogen ions which combine to form hydrogen gas.

State two uses of washing soda.

Used to remove permanent hardness of water, and in glass, soap, and paper industries.

How is Plaster of Paris prepared and where is it used?

It is prepared by heating gypsum; used for making casts, sculptures, decorative designs, and filling wall cracks.

What is bleaching powder? Give its uses.

Bleaching powder (CaOCl2) is used for disinfecting water, bleaching laundry, and as an oxidising agent in chemical industries.

Why do ant stings usually cause pain and how can it be treated?

Ant stings inject formic acid causing pain; applying a base like baking soda neutralizes the acid and gives relief.

What safety precautions should be taken when diluting concentrated acids?

Always add acid to water slowly with stirring to avoid splashes and excessive heat which can cause burns or break glass.

Explain the process of dilution of acids and why is it important?

Dilution involves adding water to an acid to lower its concentration, making it safer for use and handling.

What is meant by water of crystallization?

Water of crystallization is the fixed number of water molecules chemically bonded with salts in their crystalline form.

How are acids and bases classified as strong or weak?

Strong acids/bases completely ionize in water; weak acids/bases only partially ionize. Examples: HCl (strong acid), CH3COOH (weak acid).

What is the role of hydrochloric acid in the stomach?

Hydrochloric acid aids digestion in the stomach and maintains a low pH to help break down food.

What is the chemical formula of baking soda and its primary use?

The formula is NaHCO3 and it is mainly used in baking and as an antacid.

What are acid-base indicators and name a few?

Indicators are substances like litmus, phenolphthalein, and methyl orange that change color in acids and bases to identify their nature.

What is the neutralization reaction?

A neutralization reaction is when an acid reacts with a base to form a salt and water, cancelling out each other's properties.

Define salts in the context of acids and bases.

Salts are ionic compounds formed when acids react with bases or metals, consisting of cations from the base and anions from the acid.

What are the common properties of bases?

Bases are bitter, slippery to touch, turn red litmus blue, and neutralize acids in chemical reactions.

What are acids in chemistry according to NCERT?

Acids are substances that contain hydrogen and can donate hydrogen ions (H+) to other substances. They have a sour taste and turn blue litmus paper red.

Acids, Bases and Salts Class 10 NCERT QnA, Reactions, Indicators, Uses

Q1: Name two natural indicators for acids and bases.

Litmus and turmeric.

Q2: What is the pH of a neutral solution?

7

Q3: Which gas is evolved when acid reacts with metal?

Hydrogen gas.

Q4: State the chemical formula of baking soda.

\(\mathrm{NaHCO_3}\)

Q5: Write the formula of Plaster of Paris.

\(\mathrm{CaSO_4·\frac{1}{4}H_2O}\)

Q6: What is the colour of phenolphthalein in acid?

Colourless.

Q7: Which acid is present in vinegar?

Acetic acid (ethanoic acid).

Q8: Name any one strong acid.

Hydrochloric acid (HCl).

Q9: Sodium chloride is commonly known as?

Common salt.

Q10: Write one use of bleaching powder.

It is used for disinfecting drinking water.

Q11: What is the chemical formula of washing soda?

\(\mathrm{Na_2CO_3·10H_2O}\)

Q12: Which acid is found in lemon juice?

Citric acid.

Q13: What are alkalis?

Water soluble bases.

Q14: Give an example of a neutralization reaction.

\(\mathrm{NaOH + HCl \rightarrow NaCl + H_2O}\)

Q15: Name the acid present in the human stomach.

Hydrochloric acid (HCl).

Q1: What happens to blue litmus when dipped in acid?

It turns red.

Q2: State the effect of base on turmeric paper.

Base turns turmeric paper reddish brown.

Q3: What is the importance of pH in our daily life?

pH helps us test acidity in food, causes tooth decay, and guides soil treatment for agriculture.

Q4: How is sodium hydroxide prepared from brine?

By electrolysis of brine solution, \(\mathrm{NaOH,\, Cl_2,\, \text{and }H_2}\) are produced (chlor-alkali process).

Q5: What happens when \(\mathrm{CO_2}\) is passed through lime water first for a short time and then for a long time?

Short: Turns milky (forms \(\mathrm{CaCO_3}\)); Long: Milkiness disappears (forms soluble \(\mathrm{Ca(HCO_3)_2)}\).

Q6: Why should curd and sour substances not be kept in brass or copper vessels?

Acids in them react with the metal to form harmful salts.

Q7: List two uses of baking soda.

Used as antacid and in baking as a leavening agent.

Q8: What type of salt is formed in neutralization between strong acid and weak base?

Acidic salt.

Q9: Define universal indicator.

A mixture of indicators that shows a wide range of colours for different pH values.

Q10: Why does distilled water not conduct electricity?

It lacks ions and so cannot conduct electricity.

Q1: Explain the pH change in tooth decay and its prevention.

Tooth decay occurs below pH 5.5; prevented by using toothpastes which are basic.

Q2: Explain the manufacture of sodium hydroxide by the chlor-alkali process.

Electrolysis of brine solution yields NaOH (at cathode), \(\mathrm{Cl_2}\) (at anode), and \(\mathrm{H_2}\) (at cathode).

Q3: What are the chemical properties of acids with bases, metals, and carbonates?

Acids neutralize bases (form salt + water), react with metals (evolve \(\mathrm{H_2}\)), and react with carbonates (form \(\mathrm{CO_2}\), salt, water).

Q4: Describe the preparation, reaction and uses of washing soda.

Prepared by heating baking soda, reacts as cleansing agent, used in glass, soap & paper industry.

Q5: Explain with equations:
(a) Acid with metal carbonate
(b) Base with non-metallic oxide
(c) Acid with base

(a) Acid + carbonate \(\rightarrow\) salt + \(\mathrm{CO_2}\) + water;
(b) Base + \(\mathrm{CO_2}\) \(\rightarrow\) salt + water;
(c) Acid + base \(\rightarrow\) salt + water.

Q1: 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?

Identification:

Dip the red litmus strip in the first test tube.

If it turns blue, this tube contains the base. You now have a blue litmus strip.
If it remains red, this tube is either distilled water or acid. Proceed to the next step with the same (unaltered) strip.

If the first test did not turn blue, use the same red strip on the second test tube.

If it turns blue now, this tube contains the base.
If it still stays red, the only remaining tube is the base by elimination.

Distinguish distilled water from acid:

Once you have a blue litmus (from base identification), dip the blue side into the remaining two test tubes that kept the strip red.
In acid, the blue litmus will turn red again; in distilled water, it will remain blue.

Q2: Why should curd and sour substances not be kept in brass and copper vessels?

Curd and sour substances should not be kept in brass or copper vessels because these substances contain acids (like lactic acid in curd). When acids react with copper or brass (which is an alloy of copper and zinc), they form harmful and poisonous salts (such as copper salts). Therefore; It is unsafe to store curd and sour foods in brass or copper vessels.

Q3: 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?

When an acid reacts with metal it produces salt and hydrogen gas is liberated.

\[\boxed{\mathrm{\text{Metal}+\text{Acid}\rightarrow \text{Salt} + H_2}} \]

Example:
When zinc \(\mathrm{Zn}\) reacts with dilute sulfuric acid \(\mathrm{H_2SO_4}\), hydrogen gas is produced. \[Zn + H_2SO_4 \rightarrow ZnSO_4 + H_2\]

Testing for Hydrogen Gas:

Collect the gas in a test tube.
Bring a burning splint near the mouth of the test tube.
If hydrogen gas is present, it will burn with a 'pop' sound.

Q4: Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.

Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Calcium chloride is one product.

Effervescence and a gas that extinguishes a candle point is carbon dioxide \(\mathrm{CO_2}\) (which does not support combustion).

If one product is calcium chloride \(\mathrm{CaCl_2}\), then metal compound A is most likely calcium carbonate \(\mathrm{CaCO_3}\)

\[\boxed{\tiny\mathrm{CaCO_3 + HCl\rightarrow CaCl_2 + CO_2 + H_2O}} \]

Q5: Why do HCl, HNO3 , etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?

Hydrochloric acid (HCl), nitric acid (HNO3), and similar acids show acidic character in aqueous solutions because they release hydrogen ions (H?) when dissolved in water. These free H? ions are responsible for the acidic nature—they can turn litmus red and react with bases and metals.

Alcohol and glucose, on the other hand, do not show acidic character in aqueous solution because they do not release H? ions (protons) when dissolved in water. Their molecules remain intact (no ionisation to produce H?), so they do not change litmus or react like acids.

Q6: Why does an aqueous solution of an acid conduct electricity?

Acidic solutions conduct electricity because their molecules break into ions in water, which carry the electrical current.

Q7: Why does dry HCl gas not change the colour of the dry litmus paper?

Dry HCl gas does not change the colour of dry litmus paper because it does not release hydrogen ions \(\mathrm{(H^+)}\) in the absence of water. For an acid to show its acidic character and change the colour of litmus paper, it must ionise—and ionisation only happens when HCl dissolves in water to form ions.

Q8: While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?

When water is added directly to concentrated acid, the heat produced may cause the acid to splash out (because the reaction is highly exothermic and sudden heating can cause boiling/bursting). This can result in burns or injury.

If acid is slowly added to water:

The heat is absorbed by the larger amount of water
The mixture is diluted slowly and safely by adding the acid in small amounts, with constant stirring, which helps evenly distribute the heat and prevent any sudden splashing.
The risk of splashing and accidents is greatly reduced

Q9: How is the concentration of hydronium ions \(\mathrm{(H_3 O^+)}\) affected when a solution of an acid is diluted?

When a solution of an acid is diluted by adding more water, the concentration of hydronium ions \(\mathrm{(H_3 O^+)}\) decreases.

This is because the added water increases the total volume of the solution, causing the hydronium ions to become more spread out.

Although the actual number of hydronium ions in the solution changes very little, their concentration—that is, the number of ions per unit volume—becomes less.

As a result, the acidic strength of the solution also decreases on dilution.

Thus, diluting an acid reduces the concentration of hydronium ions in the solution.

Q10: How is the concentration of hydroxide ions \(\mathrm{(OH^-)}\) affected when excess base is dissolved in a solution of sodium hydroxide?

When excess base is dissolved in a solution of sodium hydroxide (NaOH), the concentration of hydroxide ions \(\mathrm{(OH^-)}\) in the solution increases. Sodium hydroxide is a strong base, and when it dissolves in water, it completely dissociates to produce hydroxide ions. If more base, such as potassium hydroxide or additional sodium hydroxide, is added, more \(\mathrm{(OH^-)}\) ions are introduced into the solution. This means that the total amount of hydroxide ions per unit volume (their concentration) continues to rise as more base is dissolved, making the solution even more basic.

However, it is important to note that there is a limit to how much base can dissolve in water—once the solution becomes saturated, any extra base added will not dissolve and will remain as a solid. But up to this saturation point, dissolving excess base increases the concentration of \(\mathrm{(OH^-)}\) ions in a sodium hydroxide solution.

Q11: 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?

Solution A: pH = 6
Solution B: pH = 8

Solution A has higher hydrogen ion concentration and is acidic.
Solution B has lower hydrogen ion concentration and is basic.

Q12: What effect does the concentration of \(\mathrm{H^+(aq)}\) ions have on the nature of the solution?

The concentration of hydrogen ions \(\mathrm{H^+(aq)}\) in a solution directly affects its nature:

If the concentration of \(\mathrm{H^+(aq)}\) ions is high, the solution is acidic.
If the concentration of \(\mathrm{H^+(aq)}\) ions is low, the solution is basic (or alkaline).

Summary:

Greater \(\mathrm{H^+(aq)}\) ions concentration makes the solution more acidic.
Lower \(\mathrm{H^+(aq)}\) ions concentration makes it less acidic (or even basic).

Q13: Do basic solutions also have \(\mathrm{H^+(aq)}\) ions? If yes, then why are these basic?

Yes, basic solutions do have \(\mathrm{H^+(aq)}\) ions, but their concentration is very low compared to acidic solutions. In basic (alkaline) solutions, there are many more hydroxide ions \(\mathrm{OH^-(aq)}\) than hydrogen ions \(\mathrm{H^+(aq)}\).

Why are these basic?

A solution is considered basic when the concentration of \(\mathrm{OH^-(aq)}\) ions is greater than \(\mathrm{H^+(aq)}\) ions.
Even though \(\mathrm{H^+(aq)}\) ions are present, they are outnumbered by \(\mathrm{OH^-(aq)}\) ions, so the solution shows basic properties.

Summary:

Basic solutions have a small amount of \(\mathrm{H^+(aq)}\) ions but the dominance of \(\mathrm{OH^-(aq)}\) ions makes them basic.
The lower the \(\mathrm{H^+}\) ion concentration compared to \(\mathrm{OH^-}\), the stronger the basic nature of the solution.

Q14: Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?

A farmer would treat the soil of his fields with quick lime (calcium oxide), slaked lime (calcium hydroxide), or chalk (calcium carbonate) when the soil is too acidic (has a low pH). Acidic soils can harm crop growth and reduce yield. Adding these substances neutralizes the excess acidity by reacting with the acids in the soil, raising the soil's pH and making it more suitable for farming. This process is called liming.

Q15: What is the common name of the compound \(\mathrm{Ca(ClO)_2}\) ?

The common name of the compound \(\mathrm{Ca(ClO)_2}\) is bleaching powder.

Q16: Name the substance which on treatment with chlorine yields bleaching powder.

The substance which, on treatment with chlorine, yields bleaching powder is calcium hydroxide \(\mathrm{Ca(OH)_2)}\), also known as slaked lime.

Q17: Name the sodium compound which is used for softening hard water.

The sodium compound used for softening hard water is sodium carbonate \(\mathrm{Na_2CO_3)}\), also known as washing soda.

Q18: What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.

When a solution of sodium hydrocarbonate (sodium hydrogen carbonate, also called sodium bicarbonate, \(\mathrm{NaHCO_3}\)) is heated, it decomposes to form sodium carbonate \(\mathrm{Na_2CO_3}\), water \(\mathrm{H_2O}\), and carbon dioxide gas \(\mathrm{CO_2}\).

\[\begin{aligned} \scriptsize \mathrm{2NaHCO_3(s)\xrightarrow{\Delta}} &\scriptsize\mathrm{Na_2CO_3(s)}\\ &\scriptsize\mathrm{+H_2O(l) + CO_2(g)} \end{aligned}\]

Summary: On heating, sodium hydrocarbonate gives off carbon dioxide gas and water, leaving behind sodium carbonate.

Q19: Write an equation to show the reaction between Plaster of Paris and water.

\[\begin{aligned}\scriptsize\boxed{\hspace{0.2cm}\underset{\text{Plaster of Paris}}{\mathrm{CaSO_4}.\frac{1}{2}H_2O}\mathrm{+\frac{3}{2}H_2O}\rightarrow\underset{\text{Gypsum}}{CaSO_4.2H_2O}\hspace{0.2cm}} \end{aligned}\]

Acids, Bases and Salts-QnA

TRIGONOMETRIC FUNCTIONS-Exercise 3.2

TRIGONOMETRIC FUNCTIONS-Exercise 3.1