Common acids and alkalis: แบบฝึกหัด

In the science laboratory, which of the following substances is commonly used to test for the presence of carbon dioxide gas, turning from clear to milky or cloudy?

When comparing common household substances, which of the following pairs correctly identifies the nature of the substance and its likely effect on universal indicator?

An experiment is conducted where a piece of marble (calcium carbonate, \(CaCO_3\)) is placed into an open beaker containing dilute hydrochloric acid (\(HCl\)) sitting on an electronic balance. During the reaction, bubbles are observed. Which statement correctly describes the change in the reading of the balance and the principle of conservation of mass?

Which of the following common acids is widely used in industry for the manufacture of explosives and nitrogen-based fertilizers?

Which of the following statements accurately describes a common property of alkalis?

Name a common alkali used in the science laboratory and state the characteristic taste that is generally associated with alkaline substances.

State one advantage and one disadvantage of using a digital pH meter instead of universal indicator paper for measuring the acidity of a soil sample.

In the event of an alkali splash to the eyes, describe the immediate emergency treatment required and explain why neutralising the alkali with a weak acid is a dangerous practice.

A student is investigating three unlabelled solutions in a school laboratory: Solution A, Solution B, and Solution C. He performs several tests and records the following observations:

1. When a piece of blue litmus paper is dipped into Solution A, it turns red.
2. When Solution B is touched with a gloved finger, it feels slippery or soapy.
3. Solution C does not change the colour of either red or blue litmus paper.

(a) Based on the observations, classify each solution as acidic, alkaline, or neutral. (3 points)

(b) If universal indicator solution is added to Solution A, what colour (such as red, green, or purple) is most likely to be observed? (1 point)

(c) What is the most likely pH value of Solution C at room temperature? (1 point)

(d) State one laboratory safety precaution that must be followed when handling unknown acids and alkalis. (1 point)

A science class is investigating various household liquids. They are given three unlabelled solutions: Solution X (lemon juice), Solution Y (distilled water), and Solution Z (liquid drain cleaner containing sodium hydroxide).

(a) Identifying the Solutions:
Design a simple, safe experiment using only universal indicator paper to correctly identify Solution X, Solution Y, and Solution Z. State your expected observations for each solution (e.g., colour changes).

(b) Neutralisation Reaction Analysis:
The teacher then reveals that Solution X is lemon juice (primarily citric acid) and Solution Z is liquid drain cleaner (sodium hydroxide). If a student were to slowly add Solution X (acid) to Solution Z (alkali) until neutralisation occurs:
(i) Describe how the pH of Solution Z would generally change as Solution X is added, and what pH value would indicate the neutralisation point.
(ii) Write the word equation for the neutralisation reaction between citric acid and sodium hydroxide.

(c) Hazards and Environmental Responsibility:
Both concentrated acids and concentrated alkalis are corrosive.
(i) Explain, in terms of chemical action, why concentrated solutions of strong alkalis like sodium hydroxide are dangerous to human skin.
(ii) Suggest one practical safety precaution that must be taken when handling such concentrated corrosive liquids in a laboratory.
(iii) Describe one negative environmental consequence of improperly disposing of concentrated acidic or alkaline wastewater into a river.