Question:

A solution of an acid has [H+]=2×105\left[ H ^{+}\right]=2 \times 10^{-5}. Find out the concentration of OHOH ^{-}ions.

Updated On: Jul 28, 2022
  • 5×1010N5 \times 10^{-10} N
  • 4×1010N4 \times 10^{-10} N
  • 2×105N2 \times 10^{-5} N
  • 9×104N9 \times 10^{-4} N
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The Correct Option is A

Solution and Explanation

[H]+[OH]=Kw[H]^{+}\left[O H^{-}\right]=K_{w} 2×105×[OH]=1×10142 \times 10^{-5} \times\left[O H^{-}\right]=1 \times 10^{-14} [OH]=1×10142×105[O H^-]=\frac{1 \times 10^{-14}}{2 \times 10^{-5}} =0.5×109=0.5 \times 10^{-9} =5×1010=5 \times 10^{-10}
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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