Measuring pH for acids and alkalis ：練習問題

What pH value is typically associated with a strong acid?

A student has two clear, colourless liquids in beakers. Liquid A has a pH of \(2.5\) and Liquid B has a pH of \(5.5\). Which of the following statements correctly compares the two liquids and the best method to distinguish their exact pH values?

A student has two solutions, X and Y. Solution X has a pH of 3, and solution Y has a pH of 9. When both solutions are diluted by adding 100 mL of distilled water to 10 mL of each solution, what is the most likely change in their pH values?

Which of the following pH values represents a strongly alkaline solution?

Why is a pH meter generally considered more suitable than universal indicator paper for measuring the pH of a sample of red wine?

What is the primary function of the pH scale in chemistry?

A student wants to use a red hibiscus flower extract as a natural indicator. Describe the experimental steps the student should take to determine if this extract is an effective acid-alkali indicator.

A body of water is contaminated, causing its pH to drop from \(6.8\) to \(5.0\). Calculate the approximate fold increase in hydrogen ion concentration, \([H^+]\), and suggest a suitable substance for large-scale neutralisation to restore the water closer to neutrality.

A student is conducting experiments to determine the acidity and alkalinity of various household substances using different measurement tools.

(a) State the pH value of a neutral substance, such as distilled water, at room temperature. (1 point)

(b) When testing a sample of oven cleaner, the student observes that the universal indicator paper turns dark purple. Based on the pH scale, is this substance acidic, alkaline, or neutral? (1 point)

(c) The student finds that lemon juice has a pH value of approximately \(2.0\). Classify lemon juice as an acid or an alkali. (1 point)

(d) Name one electronic instrument that can be used to measure the pH of a solution and display the result as a precise numerical value. (1 point)

A laboratory technician uses different tools to measure the pH of three unknown solutions. The observations are recorded below:

Solution X: Turns universal indicator paper orange (Estimated pH \(3-4\)).
Solution Y: Turns universal indicator paper green (Estimated pH \(7\)).
Solution Z: A digital pH meter shows a reading of \(11.45\).

(a) Based on the data, classify Solution X and Solution Z as acidic, neutral, or alkaline. (2 points)

(b) Explain one reason why the technician used a digital pH meter for Solution Z instead of universal indicator paper if an exact value was required. (2 points)

(c) If Solution X is a common household acid like vinegar, name the specific acid it likely contains. (1 point)