Grade 9 Natural Sciences Test: Acids, Bases and Reactions - Free Printable

Here are the answers to the questions on the worksheet, worked through step-by-step.

Question 1.1
* Logic: Acids are substances that release hydrogen ions ($H^+$) when dissolved in water. While some acids contain oxygen (like sulfuric acid) or carbon (like carbonic acid), the one element that *every* acid must have is Hydrogen.
* Answer: D (hydrogen)

Question 1.2
* Logic: The pH scale measures how acidic or alkaline a substance is.
* Acids have a low pH (0–6).
* Neutral is 7.
* Alkalis (bases) have a high pH (8–14).
* If you add an alkali (high pH) to an acid (low pH), you are neutralizing it. The pH value will go up towards 7.
* Answer: C (increases)

Question 1.3
* Logic: We need to find the wrong match.
* A: $HNH_4OH$ is written strangely (likely a typo for $NH_4OH$), but "Nitric acid" is $HNO_3$. This is a mismatch.
* B: $H_2SO_4$ is indeed Sulphuric acid. (Correct)
* C: $HCl$ is indeed Hydrochloric acid. (Correct)
* D: $H_2CO_3$ is indeed Carbonic acid. (Correct)
* Since the question asks for the incorrect combination, A is the answer.
* Answer: A

Question 1.4
* Logic: Litmus paper is an indicator used to test acidity.
* Blue litmus paper turns red in acid.
* Red litmus paper turns blue in alkali.
* If you put blue litmus paper in an acid, it changes color to red. If you look at the options, "red" is not listed, but typically in these multiple-choice questions, if the specific change isn't listed, one might look for the result. However, looking closely at the options: A (yellow), B (green), C (blue).
* *Correction/Refinement:* Wait, usually the options are "Red", "Blue", "Purple". Let's re-read the visible options. A: yellow, B: green, C: blue.
* Actually, blue litmus stays blue in a base, but turns red in an acid.
* Let's look at the options again. A: yellow, B: green, C: blue. None of these are "Red". Is it possible the question implies what color it *doesn't* change to? Or is there a typo in my reading?
* Let's re-evaluate standard indicators. Universal indicator turns red/orange/yellow in acid. Litmus turns red.
* *Self-Correction:* Often in poorly printed worksheets, the options might be cut off or I might be misinterpreting. However, strictly speaking, blue litmus turns red. If "Red" isn't an option, let's look at the remaining text. Ah, looking at the layout, option D is likely "Red" but is obscured by the watermark. Let's assume the standard answer is Red.
* *Wait, let's look closer at the image.* The options are A yellow, B green, C blue. There is a D option hidden by the watermark. In an acid, blue litmus turns Red. Since A, B, and C are incorrect colors for acid (Yellow/Green are universal indicator colors, Blue is the starting color), the answer must be the hidden option D.
* *Alternative interpretation:* If the question is "The colour of blue litmus paper in an acid is...", the answer is Red. If the options provided are strictly A, B, C, then none are correct. However, usually, these questions have "Red" as an option. Let's assume the answer is Red.
* *Let's check the options again.* A: yellow, B: green, C: blue. D is covered. The answer is definitely Red. I will select the option that corresponds to Red. If I must choose from visible text, none fit, but logically it is Red.
* *Let's try to infer from the watermark.* The watermark covers D. I will state the answer is Red.

Question 1.5
* Logic: The reaction is between an Acid (Hydrochloric acid) and a Metal (Lithium).
* General Rule: Acid + Metal $\rightarrow$ Salt + Hydrogen Gas.
* Reaction: $HCl + Li \rightarrow LiCl + H_2$.
* Answer: B (hydrogen gas)

Question 1.6
* Logic: The reaction is between an Acid (Hydrochloric acid) and a Base/Alkali (Sodium hydroxide).
* General Rule: Acid + Base $\rightarrow$ Salt + Water.
* Reaction: $HCl + NaOH \rightarrow NaCl + H_2O$.
* Answer: A (water)

Question 1.7
* Logic: We need to find a Base.
* A: $KOH$ (Potassium Hydroxide) - This is a strong base/alkali.
* B: $KCl$ (Potassium Chloride) - This is a salt.
* C: $CH_3OH$ (Methanol) - This is an alcohol.
* D: $CH_3COOH$ (Ethanoic acid) - This is an acid.
* Answer: A

Question 1.8
* Logic: The process of adding an alkali to an acid (or vice versa) to cancel out the acidity/basicity is called neutralization.
* Answer: A (neutralisation)

Question 2.1
* Task: General reaction for an acid with a Base.
* Answer: Acid + Base $\rightarrow$ Salt + Water

Question 2.2
* Task: General reaction for an acid with a Carbonate.
* Answer: Acid + Carbonate $\rightarrow$ Salt + Water + Carbon Dioxide

Question 2.3
* Task: General reaction for an acid with a Metal.
* Answer: Acid + Metal $\rightarrow$ Salt + Hydrogen

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Final Answer:
1.1 D
1.2 C
1.3 A
1.4 [Red] (Note: Option D is covered by the watermark, but the correct color is Red)
1.5 B
1.6 A
1.7 A
1.8 A
2.1 Acid + Base $\rightarrow$ Salt + Water
2.2 Acid + Carbonate $\rightarrow$ Salt + Water + Carbon Dioxide
2.3 Acid + Metal $\rightarrow$ Salt + Hydrogen