Question:

Which among the following has highest pH?

Updated On: Dec 10, 2023
  • 1 M H2SO4

  • 1 M HCl
  • 0.1 M NaOH
  • 1 M NaOH
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The Correct Option is D

Solution and Explanation

The pH scale measures the acidity or alkalinity of a solution. A higher pH value indicates a more alkaline or basic solution, while a lower pH value indicates a more acidic solution. Among the options provided: 
(A) 1 M H2SO4: Sulfuric acid (H2SO4) is a strong acid and has a low pH. It is highly acidic. 
(B) 1 M HCl: Hydrochloric acid (HCl) is also a strong acid and has a low pH. It is highly acidic. 
(C) 0.1 M NaOH: Sodium hydroxide (NaOH) is a strong base and has a high pH. It is alkaline. 
(D) 1 M NaOH: Sodium hydroxide (NaOH) is a strong base and has a high pH. It is alkaline. 
Comparing options (C) and (D), both solutions contain the same base, sodium hydroxide (NaOH), but option (D) has a higher concentration (1 M) compared to option (C) (0.1 M). Since pH is a logarithmic scale, a higher concentration of a strong base will result in a higher pH value. 
Therefore, option (D) 1 M NaOH has the highest pH among the given options.

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Concepts Used:

Acids and Bases

Acid is any hydrogen-containing substance that is capable of donating a proton (hydrogen ion) to another substance. Base is an ion or molecule capable of accepting a hydrogen ion from acid. 

Physical Properties of Acids and Bases

Physical PropertiesACIDSBASES
TasteSourBitter
Colour on Litmus paper Turns blue litmus redTurns red litmus blue
Ions produced on dissociationH+OH-
pH<7 (less than 7)>7 (more than 7)
Strong acidsHCl, HNO3, H2SO4NaOH, KOH
Weak AcidsCH3COOH, H3PO4, H2CO3NH4OH

Chemical Properties of Acids and Bases

Type of ReactionAcidBases
Reaction with Metals

Acid + Metal → Salt + Hydrogen gas (H2)

E.g.,

Zn(s)+ dil. H2SO4 → ZnSO(Zinc Sulphate) + H2

Base + Metal → Salt + Hydrogen gas (H2)

E.g.,

2NaOH +Zn → Na2ZnO2 (Sodium zincate) + H2

Reaction with hydrogen carbonates (bicarbonate) and carbonates

Metal carbonate/Metal hydrogen carbonate + Acid → Salt + Carbon dioxide + Water

E.g., HCl+NaOH → NaCl+ H2O

2. Na2CO3+ 2 HCl(aq) →2NaCl(aq)+ H2O(l) + CO2(g)

3. Na2CO3+ 2H2SO4(aq) →2Na2SO4(aq)+ H2O(l) + CO2(g)

4. NaHCO3+ HCl → NaCl+ H2O+ CO2

Base+ Carbonate/ bicarbonate → No reaction
Neutralisation Reaction

Base + Acid → Salt + Water

E.g., NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

Base + Acid → Salt + Water

E.g., CaO+ HCl (l) → CaCl2 (aq)+ H2O (l)

Reaction with Oxides

Metal oxide + Acid → Salt + Water

E.g., CaO+ HCl (l) → CaCl2 (aq)+ H2O (l)

Non- Metallic oxide + Base → Salt + Water

E.g., Ca(OH)2+ CO2 → CaCO3+ H2O

Dissolution in Water

Acid gives H+ ions in water.

E.g., HCl → H+ + Cl-

HCl + H2O → H3O+ + Cl–

Base gives OH- ions in water.

Read more on Acids, Bases and Salts