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Understanding Acids Worksheet

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Understanding Acids Worksheet

A science team has found four unlabelled solutions in a teaching laboratory. Use the information and safe testing methods below to classify them and explain how acids behave. Do not taste or touch laboratory chemicals.

Clue file: acids in water

An acid is a substance that produces hydrogen ions (H⁺) when it dissolves in water. The pH scale is commonly shown from 0 to 14: values below 7 are acidic, 7 is neutral, and values above 7 are alkaline. The lower the pH, the more acidic a solution is. pH alone does not tell you the concentration of an acid. Acids can react with some metals, producing hydrogen gas. The rate and extent depend on the acid, metal, concentration and conditions. Some acids are corrosive, so laboratory acids must never be tasted or handled without appropriate instructions and protective equipment. Vinegar contains acetic acid, and lemon juice contains citric acid.

1.The team tests four solutions and records pH 2, 6, 8 and 12. Which two are acidic? Explain using the pH scale.

2.Put the four recorded pH values in order from most acidic to most alkaline. What does the order tell you about acidity?

3.When hydrochloric acid dissolves in water, which ion does it produce that is characteristic of acids?

Hydrogen ion (H⁺)
Sodium ion (Na⁺)
Oxygen ion (O²⁻)
Calcium ion (Ca²⁺)

4.A student says, “A solution with pH 2 must be more concentrated than one with pH 5.” Is that conclusion justified by pH alone? Explain.

5.Complete the sentence: Vinegar contains acid, and lemon juice contains acid.

6.Match each substance to the acid commonly associated with it.

Vinegar
Citrus fruit
Stomach gastric juice

Citric acid
Acetic acid
Hydrochloric acid

Test-bench evidence

A supervised class tests small pieces of zinc in dilute hydrochloric acid. They observe bubbles forming on the zinc. A glowing splint is not used near the reaction, and the gas is not deliberately ignited.

7.What does the bubbling suggest is happening when zinc reacts with dilute hydrochloric acid? Name the gas produced.

8.Write a word equation for the reaction between zinc and hydrochloric acid. The products are zinc chloride and hydrogen.

9.Choose the safest and most useful first test for an unknown laboratory solution, and explain why it is suitable.

10.A class has pH paper, a dropper, goggles and four labelled sample wells. Describe a safe, fair method for checking whether one unknown solution is acidic. Include how to avoid contaminating the sample.