PH scale test answers, Grade 8 science (PDF)

The questions are on the pH scale test. Take it under real conditions before reading the mark scheme.

Quick answer: Acids have a pH below 7, alkalis have a pH above 7, and a neutral liquid such as pure water has a pH of exactly 7. This mark scheme gives the model answers and the marks for the 8 questions of the grade 8 science test on pH scale, from indicators to dilution plan, with the equivalent answers to accept.

PH scale test answers and mark scheme for grade 8 science (free PDF download)

This is the pH scale test answers for grade 8 science, with the marks for each answer. First sit the test without notes, then mark it here and revise with the lesson.

Marks are shown in each model answer. Accept any correct equivalent wording, and give error-carried-forward credit for later parts when the method is right.

Level: Grade 8 science (Year 9 · Class 8) · Curriculum: MS-PS1-2

Contents

PH scale test answers: answers and marks

Question 1 Indicators (2 marks)

Red.
Green.

Marking: 1 mark each.

Question 2 Reading the scale (3 marks)

R (pH 7).
P (pH 1).
S (pH 12).

Marking: 1 mark each.

Question 3 Dilution by 100 (2 marks)

Factor 100 raises the pH by 2, so the new pH is 5.

Marking: 1 mark for the rise of 2, 1 mark for the answer 5.

Question 4 Comparing acidity (3 marks)

3 steps, so 10 × 10 × 10 = 1000 times.
Both are acidic, since each pH is below 7.

Marking: 1 mark for 3 steps, 1 for 1000; 1 mark for acidic.

Question 5 Why not alkaline? (3 marks)

Water is neutral with pH 7. Dilution spreads the acid out, so the pH moves up towards 7. The acid becomes weaker but the water cannot make it more basic than neutral, so the pH never goes above 7.

Marking: 1 mark water is neutral; 1 mark pH approaches 7; 1 mark never passes 7.