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pH Calculations Worksheet with Answers (Grade 11 Chemistry)

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📄 pH Calculations Worksheet with Answers (Grade 11 Chemistry)

Practise acids, bases and pH with this free Grade 11 chemistry worksheet.

This free pH calculations worksheet gives Grade 11 students 25 problems on acids, bases and the pH scale, from classifying solutions to neutralization volumes.

Students calculate pH from concentration and concentration from pH, find the pOH and pH of strong bases (including Ba(OH)2), see how dilution changes pH, and solve two neutralization problems. Every value has been calculated and reported with the correct significant figures.

  • Grade 11 Chemistry
  • 27 marks
  • 40–50 minutes
  • Worked answer key

What's in This pH Calculations Worksheet

PartSkill practisedMarks
AAcidic, basic or neutral?4
BArrhenius acids and bases4
CpH from [H3O+]4
D[H3O+] from pH3
EBases: pOH and pH4
FDilution and the logarithmic scale2
GNeutralization volumes4
HSpot the mistake2

It supports the Ontario Grade 11 chemistry curriculum expectations in the Solutions and Solubility unit.

The pH Scale

0
1
2
3
4
5
6
7
8
9
10
11
12
13
14

← more acidicneutral (7)more basic →

pH measures how acidic or basic a solution is. Below 7 is acidic, 7 is neutral and above 7 is basic. Because the scale is logarithmic, each step of one unit means a tenfold change in [H3O+]. For more on the theory, see pH on Wikipedia.

pH and pOH Formulas

pH = −log[H3O+]  ·  pOH = −log[OH−]  ·  pH + pOH = 14.00  ·  [H3O+] = 10−pH

Strong acids (HCl, HBr, HI, HNO3, H2SO4, HClO4) and strong bases (Group 1 hydroxides, Ca(OH)2, Ba(OH)2) ionize completely, so the ion concentration comes straight from the solution's concentration. Every problem on this pH calculations worksheet uses strong acids and bases.

Worked Examples

pH of an acid

0.0050 mol/L HNO3: [H3O+] = 0.0050 mol/L, so pH = −log(0.0050) = 2.30. The concentration has 2 significant figures, so the pH has 2 decimal places.

pH of a base with two OH−

0.050 mol/L Ba(OH)2: [OH−] = 2 × 0.050 = 0.10 mol/L, pOH = 1.00, and pH = 14.00 − 1.00 = 13.00. Forgetting the factor of 2 is the most common mistake on any pH calculations worksheet. If students need a refresher on concentration, the molarity worksheet covers it.

pH Calculations Practice Problems

These match the pH calculations worksheet PDF. Assume 25 °C and report pH to the correct number of decimal places.

Part A – Acidic, Basic or Neutral?

  1. pH = 3.2
  2. pH = 7.00
  3. pH = 11.5
  4. [H3O+] = 1.0 × 10−9 mol/L

Part B – Arrhenius Acid or Base?

State acid or base, and which ion it releases in water.

  1. HCl
  2. NaOH
  3. HNO3
  4. Ca(OH)2

Part C – pH From [H3O+]

  1. Find the pH of a solution with [H3O+] = 1.0 × 10−3 mol/L.
  2. Find the pH of a solution with [H3O+] = 2.5 × 10−4 mol/L.
  3. Find the pH of 0.010 mol/L HCl.
  4. Find the pH of 0.0050 mol/L HNO3.

Part D – [H3O+] From pH

  1. Find [H3O+] for a solution with pH = 4.00.
  2. Find [H3O+] for a solution with pH = 2.70.
  3. Find [H3O+] for a solution with pH = 9.40.

Part E – Bases: pOH and pH

  1. Find the pOH and pH of 0.010 mol/L NaOH.
  2. Find the pOH and pH of 0.0025 mol/L KOH.
  3. Find the pOH and pH of 0.050 mol/L Ba(OH)2.
  4. A solution has pH = 10.50. Find its pOH and [OH−].

Part F – Dilution and the pH Scale

  1. 10.0 mL of 0.10 mol/L HCl is diluted to 1.00 L. What is the new pH?
  2. How many times more acidic is a solution with pH 3 than one with pH 5?

Part G – Neutralization

  1. HCl + NaOH → NaCl + H2O. What volume of 0.20 mol/L NaOH is needed to neutralize 30.0 mL of 0.10 mol/L HCl?
  2. H2SO4 + 2NaOH → Na2SO4 + 2H2O. What volume of 0.100 mol/L NaOH neutralizes 20.0 mL of 0.050 mol/L H2SO4?

Part H – Spot the Mistake

  1. A student calculates the pH of 0.050 mol/L Ba(OH)2 as 12.70. Explain the error and correct it.
  2. A student says a solution with pH 2 is twice as acidic as one with pH 4. Explain the error and correct it.

pH Calculations Worksheet Answer Key

Each answer shows the working. The printable key is at the end of the PDF.

Part A answers (Q1–4)
  1. pH = 3.2: Acidic
  2. pH = 7.00: Neutral
  3. pH = 11.5: Basic
  4. [H3O+] = 1.0 × 10−9 mol/L: Basic (pH = 9.00)
Part B answers (Q5–8)
  1. HCl: Acid: releases H+ in water
  2. NaOH: Base: releases OH−
  3. HNO3: Acid: releases H+
  4. Ca(OH)2: Base: releases 2 OH−
Part C answers (Q9–12)
  1. pH = −log(1.0 × 10-3) = 3.00
  2. pH = −log(2.5 × 10-4) = 3.60
  3. pH = −log(0.010) = 2.00
  4. pH = −log(5.0 × 10-3) = 2.30
Part D answers (Q13–15)
  1. [H3O+] = 10−4.00 = 1.0 × 10-4 mol/L
  2. [H3O+] = 10−2.70 = 2.0 × 10-3 mol/L
  3. [H3O+] = 10−9.40 = 4.0 × 10-10 mol/L
Part E answers (Q16–19)
  1. pOH = −log(0.010) = 2.00; pH = 14.00 − 2.00 = 12.00
  2. pOH = −log(0.0025) = 2.60; pH = 14.00 − 2.60 = 11.40
  3. pOH = −log(0.10) ([OH−] = 2 × 0.050 = 0.10 mol/L) = 1.00; pH = 14.00 − 1.00 = 13.00
  4. pOH = 14.00 − 10.50 = 3.50; [OH−] = 10−3.50 = 3.2 × 10-4 mol/L
Part F answers (Q20–21)
  1. c = (0.10 × 10.0) ÷ 1000 = 1.0 × 10-3 mol/L; pH = 3.00
  2. Each pH unit is a factor of 10: 10(5 − 3) = 100 times more acidic.
Part G answers (Q22–23)
  1. n(HCl) = 0.10 × 0.0300 = 0.0030 mol = n(NaOH); V = 0.0030 ÷ 0.20 = 0.015 L = 15.0 mL
  2. n(H2SO4) = 0.050 × 0.0200 = 0.0010 mol; n(NaOH) = 2 × 0.0010 = 0.0020 mol; V = 0.0020 ÷ 0.100 = 20.0 mL
Part H answers (Q24–25)
  1. Ba(OH)2 releases 2 OH−, so [OH−] = 0.10 mol/L, pOH = 1.00 and pH = 13.00.
  2. pH is logarithmic: a difference of 2 units is 102 = 100 times more acidic.

5 Common pH Mistakes

  1. Forgetting the second OH−. Ca(OH)2 and Ba(OH)2 double [OH−].
  2. Treating pH as linear. pH 2 is 100 times more acidic than pH 4, not twice as acidic.
  3. Using pOH as pH for a base. Finish with pH = 14.00 − pOH.
  4. Dropping the negative sign. pH = −log[H3O+], so the answer is positive for normal concentrations.
  5. Wrong significant figures. Decimal places in pH match significant figures in the concentration.

How to Use This pH Calculations Worksheet in Class

  • Day 1: Parts A–D after introducing the pH scale and logarithms.
  • Day 2: Parts E and F with pOH.
  • Before a titration lab: Parts G and H, so students can predict their neutralization volumes.

Then check understanding with the acids and bases quiz and the acids, bases and pH scale quiz.

Frequently Asked Questions

Is this ph calculations worksheet free?

Yes. The worksheet and its worked answer key are free to download and print as a PDF, with no account needed.

How do you calculate pH?

pH = −log[H3O+]. For a strong acid, [H3O+] equals the acid concentration, so 0.010 mol/L HCl has a pH of 2.00.

How do you find the pH of a base?

Find [OH−] (remembering that Ca(OH)2 and Ba(OH)2 release two OH− each), calculate pOH = −log[OH−], then use pH = 14.00 − pOH.

How many significant figures should a pH have?

The number of decimal places in the pH equals the number of significant figures in the concentration. 2.5 × 10^−4 mol/L has two significant figures, so its pH is reported as 3.60.

Why is a pH difference of 2 a factor of 100?

The pH scale is logarithmic, so each unit is a tenfold change in [H3O+]. Two units means 10 × 10 = 100 times.

More Free Grade 11 Chemistry Resources

Ready to practise? Download the free pH calculations worksheet PDF (use the Download button above), print it double-sided, and keep the answer key pages for marking.

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