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Acids and Bases - Properties of Acids and Bases

Grade 9IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Acids are substances that release hydrogen ions H+H^+ when dissolved in water. Common examples include hydrochloric acid HClHCl and sulfuric acid H2SO4H_2SO_4.

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Bases are substances that react with acids to form salt and water. Soluble bases are called alkalis and release hydroxide ions OH−OH^- in aqueous solutions, such as sodium hydroxide NaOHNaOH.

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The pHpH scale ranges from 00 to 1414, measuring the concentration of H+H^+ ions. Acids have a pH<7pH < 7, neutral substances (like pure H2OH_2O) have a pH=7pH = 7, and bases have a pH>7pH > 7.

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Indicators change color depending on pHpH. For example, litmus turns red in acids and blue in bases; phenolphthalein remains colorless in acids but turns pink in bases.

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Acids react with reactive metals (such as MgMg or ZnZn) to produce a salt and hydrogen gas H2H_2. The presence of H2H_2 can be tested with a 'squeaky pop' test.

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Neutralization is the reaction between an acid and a base to produce water and a salt. The net ionic equation is H(aq)++OH(aq)−ightarrowH2O(l)H^+_{(aq)} + OH^-_{(aq)} ightarrow H_2O_{(l)}.

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Acids react with metal carbonates or hydrogen carbonates to produce a salt, water, and carbon dioxide gas CO2CO_2.

📐Formulae

Acid+Base→Salt+WaterAcid + Base \rightarrow Salt + Water

Acid+Metal→Salt+Hydrogen (H2)Acid + Metal \rightarrow Salt + Hydrogen\ (H_2)

Acid+Carbonate→Salt+Water+Carbon Dioxide (CO2)Acid + Carbonate \rightarrow Salt + Water + Carbon\ Dioxide\ (CO_2)

H(aq)++OH(aq)−→H2O(l)H^+_{(aq)} + OH^-_{(aq)} \rightarrow H_2O_{(l)}

2HCl(aq)+CaCO3(s)→CaCl2(aq)+H2O(l)+CO2(g)2HCl_{(aq)} + CaCO_{3(s)} \rightarrow CaCl_{2(aq)} + H_2O_{(l)} + CO_{2(g)}

💡Examples

Problem 1:

Write the balanced chemical equation for the reaction between Magnesium (MgMg) and Hydrochloric acid (HClHCl). Identify the gas produced.

Solution:

Mg(s)+2HCl(aq)→MgCl2(aq)+H2(g)Mg_{(s)} + 2HCl_{(aq)} \rightarrow MgCl_{2(aq)} + H_{2(g)}

Explanation:

In this reaction, the metal magnesium displaces hydrogen from the acid to form the salt magnesium chloride (MgCl2MgCl_2). The gas produced is hydrogen (H2H_2).

Problem 2:

Calculate the products of the neutralization reaction between Sulfuric acid (H2SO4H_2SO_4) and Potassium hydroxide (KOHKOH).

Solution:

H2SO4(aq)+2KOH(aq)→K2SO4(aq)+2H2O(l)H_2SO_{4(aq)} + 2KOH_{(aq)} \rightarrow K_2SO_{4(aq)} + 2H_2O_{(l)}

Explanation:

The acid H2SO4H_2SO_4 reacts with the base KOHKOH to form the salt potassium sulfate (K2SO4K_2SO_4) and water (H2OH_2O). This is a double displacement reaction where H+H^+ and OH−OH^- ions combine.

Problem 3:

A student adds Nitric acid (HNO3HNO_3) to Sodium Carbonate (Na2CO3Na_2CO_3). Describe the observations and provide the chemical equation.

Solution:

2HNO3(aq)+Na2CO3(s)→2NaNO3(aq)+H2O(l)+CO2(g)2HNO_{3(aq)} + Na_2CO_{3(s)} \rightarrow 2NaNO_{3(aq)} + H_2O_{(l)} + CO_{2(g)}

Explanation:

The observation would include effervescence (bubbling) due to the release of carbon dioxide gas (CO2CO_2). If this gas is passed through limewater, the limewater will turn cloudy.