Free pH and pOH MCQs with Answers

1. K, is acid association constant, large PK,, value for an acid indicates that acid is:

• A. Strong
• B. weak
• C. moderate
• D. water soluble

Explanation: if KA is smaller than pKA is large which means weak acid

2. If 9.8 g of sulfuric acid is dissolved in an excess quantity of water, it will yield _ moles of hydrogen ion ( H+) and _ mole of sulphate ions (SO4 -2).

• A. 0.1, 0.2
• B. 0.1, 0.3
• C. 0.2, 0.4
• D. 0.2, 0.1

Explanation: 9.8 grams of sulphuric acid is 0.1 moles so there will be 0.2 moles of hydrogen ions ( two hydrogens per sulphuric acid molecule) H2SO4 dissociates in 2 steps H2SO4 → H+ + HSO4- Therefore 0.1 mol H2SO4 will produce 0.1 mol H+ HSO4- ↔ H+ + SO4- Ka for this reaction is : 1.2 x 10-2 Calculate [H+] using Ka equation Ka = [H+]² / [HSO4- ] 1.2*10^-2 = [H+]² / 0.1 [H+]² = 0.1( 1.2*10^-2) [H+]² = 1.2*10^-3 [H+] = 0.035 M Total moles of H+ ions = 0.1 + 0.035 = 0.135 moles

3. Which material possesses the highest pH?

• A. Soft drinks
• B. Bananas
• C. Milk of magnesia
• D. Sea water

Explanation: The basic pH of milk of magnesia helps neutralize overactive stomach acids that cause heartburn.

4. 0.1 mole of acetic acid has been dissolved per dm3 of the solution, the percentage ionization of acetic acid will be

• A. 13
• B. 15
• C. 1.3
• D. 0.1

Explanation: A, B and D are incorrect because these are not correct percentage ionization valuesC is correct since The solution is given as CH3COOH dissociates to a small extent:CH3COOH ↔ CH3COO- + H+Calculate [H+] from the Ka equation.Ka = [H+] [[CH3COO-] / [CH3COOH]Because [H+] =[CH3COO-] and dissociation is very small, we can write the equation asKa = [H+]² / 0.1Ka = 1.8*10-51.8*10-5 = [H+]² / 0.1[H+]² = (1.8*10-5)* 0.1[H+]² = 1.8*10-6[H+] = 0.0013M% dissociation = 0.0013/0.1*100 = 1.34%

5. The 'pH' of human blood is:

• A. 6.7 - 8
• B. 7.9
• C. 7.5
• D. 7.35 - 7.4

Explanation: The pH of human blood is typically around 7.35 to 7.45, which is slightly alkaline or basic. It is important for the pH of blood to remain within this narrow range as deviations can have adverse effects on bodily functions.

6. Which one f the following has the lowest pH?

• A. 1 M HF
• B. 1 M HCL
• C. 1 m CH3COOH
• D. 1 M NaOH

Explanation: As we know that lower the pH, stronger the acid and greater the no of hydrogen ions in a solution. The acidity of an acid is measured by the ability to remove hydrogen ion.

7. What is the concentration of [H+] in the HNO3 acid solution with a PH of 3?

• A. 3
• B. -3
• C. - antilog [3]
• D. 10^-3

Explanation: pH is defined as the negative logarithm of the hydrogen ion concentration [H+]. Mathematically, it can be expressed as:pH = -log[H+]Rearranging this equation, we get:[H+] = 10-pHSubstituting the given pH of 3 in the above equation, we get:[H+] = 10^-3Therefore, the concentration of [H+] in an HNO3 acid solution with a pH of 3 is 10^-3 M.

8. Milk of magnesia is used for treatment of acidity in stomach, its formula is:

• A. Mg(OH)2
• B. MgSO4
• C. Ca(OH)2
• D. CaSO4

Explanation: Milk of magnesia is a suspension of magnesium hydroxide, with the chemical formula Mg(OH)2. It is an effective antacid that neutralizes stomach acid, providing relief from heartburn and indigestion. The reaction with stomach acid produces magnesium chloride and water, which reduces acidity. The other options, MgSO4, Ca(OH)2, and CaSO4, either have different uses or are not suitable for treating stomach acidity.

9. What is the concentration moles/liter of nitric acid solution having PH of 4?

• A. 0.0001 mol/L
• B. -4
• C. 10-4 mol/L
• D. 10-10

Explanation: To determine the concentration of nitric acid in moles per liter with a pH of 4, we apply the formula: pH = -log[H+]. Rearranging gives [H+] = 10-pH. Substituting pH = 4 yields [H+] = 10-4 = 0.0001 mol/L. Since HNO3 dissociates completely in solution, the concentration of HNO3 is equal to the concentration of H+ ions. Thus, the correct concentration is 0.0001 mol/L.Option B (-4) is incorrect because pH cannot be a negative concentration. Option C (10-4) is mathematically correct but usually expressed as 0.0001 mol/L for clarity. Option D (10-10) would relate to a much higher pH value, unsuitable for this question.

10. If the pH of the solution is 9 its OH− ions concentration is:

• A. 10−5
• B. 5
• C. 10−9
• D. 9

Explanation: As we know that,pH+pOH=14pOH=14-9=5Also, pOH=log[OH-][OH-]=antilog(pOH)[OH]=antilog (5)[OH]=10-5