$50\, mL$ of $0.02\, M \,NaOH$ solution is mixed $50\, mL$ of $0.06 \,M$ acetic acid solution, the $pH$ of resulting solution is
$\left( p K_{a}\right.$ of acetic acid is $4.76, \log 5=0.70$ )
- 5.06
- 4.06
- 5.46
- 4.46
The Correct Option is D
Solution and Explanation
Given, Volume of \(NaOH\) solution \(=50 \,mL\)
Molarity of \(NaOH\) solution \(=0.02 \,M\)
Me of \(NaOH =50 \times 0.02=1 \,meq\)
Volume of \(CH _{3} COOH\) solution \(=50 \,mL\)
Molarity of \(CH _{3} COOH =0.06\, M\)
Me of \(CH _{3} COOH =50 \times 0.06=3\, meq\)
\(1\) me of \(NaOH\) combines with \(3\) me of
\(CH _{3} COOH\) and forms \(1\) me of \(CH _{3} COONa\).
\(\therefore 2\) me of \(CH _{3} COOH\) is left.
So, it forms an acidic buffer.
Now, for an acidic buffer,
\(pH = p K_{a}+\log \left[\frac{\text { Salt }}{\text { Acid }}\right]\)
\(pH = p K_{a}+\log \frac{\left[ CH _{3} COONa \right]}{\left[ CH _{3} COOH \right]}\)
\(\therefore pH =4.76+\log \left[\frac{ l }{2}\right]\)
\(pH =4.76+\log \left(5 \times 10^{-1}\right)\)
\(pH =4.76+\log 5-\log 10\)
\(=4.76+0.70- 1\)
\(=4.46\)
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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 Properties | ACIDS | BASES |
| Taste | Sour | Bitter |
| Colour on Litmus paper | Turns blue litmus red | Turns red litmus blue |
| Ions produced on dissociation | H+ | OH- |
| pH | <7 (less than 7) | >7 (more than 7) |
| Strong acids | HCl, HNO3, H2SO4 | NaOH, KOH |
| Weak Acids | CH3COOH, H3PO4, H2CO3 | NH4OH |
Chemical Properties of Acids and Bases
| Type of Reaction | Acid | Bases |
| Reaction with Metals | Acid + Metal → Salt + Hydrogen gas (H2) E.g., Zn(s)+ dil. H2SO4 → ZnSO4 (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