Year Eight Acids and Metals Revision Flashcards

Year 8 Revision Checklist for Acids and Metals

• Students should be able to name common acids and alkalis.
• Identification of substances as acids or alkalis using indicators (e.g., universal indicator, red cabbage, litmus).
• Production of natural indicators using substances like red cabbage.
• Measurement of the strength of acids and alkalis using the $pH$ scale.
• Explanation of $pH$ changes during a neutralisation reaction.
• Planning scientific investigations, such as determining the most effective antacid.
• Stating chemical and physical properties and uses of metals.
• Writing word equations for oxidation reactions (Metal + Oxygen).
• Knowledge of the test for hydrogen gas ($\text{squeaky pop}$ test).
• Making observations and writing word equations for reactions between metals and acids.
• Deducing the names of salts formed from specific acids (hydrochloric, nitric, and sulfuric acids).
• Making observations and writing word equations for reactions between metals and water.
• Using the reactivity series to predict and write equations for displacement reactions.
• Deducing metal reactivity orders based on experimental results.
• Improving the precision of experimental results.
• Identifying independent, control, and dependent variables in scientific investigations.

Properties of Acids and Alkalis

• Acids:     * Can be corrosive (can damage skin or eyes, cause burns, or irritation).     * Have a sour taste.     * Usually react with metals.     * Examples include hydrochloric acid ($HCl$), sulfuric acid ($H_2SO_4$, containing hydrogen, sulfur, and oxygen), nitric acid ($HNO_3$, containing 5 atoms total), and ethanoic acid ($CH_3COOH$).
• Alkalis:     * Have a soapy feel.     * Have a bitter taste.     * Are often used in cleaning products like bleach or washing-up liquid.

Indicators and the $pH$ Scale

• Definition: Indicators are chemicals that change colour to show if a substance is an acid or an alkali.
• Common Indicators:     * Universal Indicator.     * Red Cabbage (turns red in acid, purple when neutral, and blue/green in alkali).     * Litmus paper.     * Phenolphthalein.     * Hydrangea plants.
• The $pH$ Scale:     * Ranges from $1$ to $14$.     * Acids: $pH$ values of $1$ to $6$. $1$ to $3$ are strong acids (red/orange); $4$ to $6$ are weak acids (yellow/light green).     * Neutral: $pH$ value of $7$ (green). Examples include distilled water and alcohol.     * Alkalis: $pH$ values of $8$ to $14$. $8$ to $10$ are weak alkalis (blue); $11$ to $14$ are strong alkalis (purple).
• Acidity Levels: A substance with a lower $pH$ is more acidic. For example, dilute hydrochloric acid ($pH = 1.0$) is more acidic than lemonade ($pH = 4.4$).

Neutralisation and Chemical Tests

• Neutralisation: When an acid and an alkali react to form a salt and water.     * $\text{Acid} + \text{Alkali} \rightarrow \text{Salt} + \text{Water}$     * Adding alkali to an acid increases the $pH$ toward $7$.     * Adding acid to an alkali decreases the $pH$ toward $7$.
• Testing for Hydrogen:     * Procedure: Light a splint and hold it to the mouth of the test tube containing the gas.     * Observation: If hydrogen is present, it will make a "squeaky pop" sound.
• Separation Techniques:     * Filtration: Used to separate solids from liquids (e.g., separating cabbage pieces from cabbage-water).     * Chromatography: Used to find out if a liquid contains more than one coloured substance.

Properties and Reactions of Metals

• Physical Properties of Metals:     * Conductors (of heat and electricity).     * Durable.     * Ductile (can be drawn into wires).     * Malleable (can be hammered into shape).     * Sonorous (make a ringing sound when hit).     * High melting point.     * Shiny appearance.
• Metal + Oxygen: Forms a metal oxide (Oxidation).     * $\text{Metal} + \text{Oxygen} \rightarrow \text{Metal Oxide}$
• Metal + Acid: Forms a salt and hydrogen gas.     * $\text{Metal} + \text{Acid} \rightarrow \text{Salt} + \text{Hydrogen}$     * The type of salt depends on the acid used:         * Hydrochloric acid ($HCl$) forms Chlorides.         * Sulfuric acid ($H_2SO_4$) forms Sulfates.         * Nitric acid ($HNO_3$) forms Nitrates.
• Reactivity Series:     * A list of metals in order of reactivity (e.g., Potassium [$K$] is highly reactive, Magnesium [$Mg$] is medium, and Copper [$Cu$] is low).
• Displacement Reactions:     * Occur when a more reactive metal takes the place of a less reactive metal in a compound.     * Example: $\text{Copper Sulfate} + \text{Magnesium} \rightarrow \text{Magnesium Sulfate} + \text{Copper}$.     * Example: $\text{Potassium Chloride} + \text{Magnesium} \rightarrow \text{No Reaction}$ (because Magnesium is less reactive than Potassium).

Extensive Word and Chemical Equations

• Metal + Acid Reactions:     * $Mg + H_2SO_4 \rightarrow \text{magnesium sulfate} + \text{hydrogen}$     * $Zn + H_2SO_4 \rightarrow \text{zinc sulfate} + \text{hydrogen}$     * $Mg + 2HNO_3 \rightarrow \text{magnesium nitrate} + \text{hydrogen}$     * $Zn + 2HNO_3 \rightarrow \text{zinc nitrate} + \text{hydrogen}$     * $Zn + 2HCl \rightarrow \text{zinc chloride} + \text{hydrogen}$     * $Co + 2HCl \rightarrow \text{cobalt chloride} + \text{hydrogen}$
• Metal Oxide + Acid Reactions:     * $\text{Metal Oxide} + \text{Acid} \rightarrow \text{Salt} + \text{Water}$     * $CuO + H_2SO_4 \rightarrow \text{copper sulfate} + \text{water}$     * $NiO + 2HNO_3 \rightarrow \text{nickel nitrate} + \text{water}$
• Metal Hydroxide + Acid Reactions:     * $\text{Metal Hydroxide} + \text{Acid} \rightarrow \text{Salt} + \text{Water}$     * $NaOH + HCl \rightarrow \text{sodium chloride} + \text{water}$     * $Ba(OH)_2 + H_2SO_4 \rightarrow \text{barium sulfate} + \text{water}$
• Metal Carbonate + Acid Reactions:     * $\text{Metal Carbonate} + \text{Acid} \rightarrow \text{Salt} + \text{Water} + \text{Carbon Dioxide}$     * $Na_2CO_3 + 2HNO_3 \rightarrow \text{sodium nitrate} + \text{water} + \text{carbon dioxide}$     * $CuCO_3 + 2HCl \rightarrow \text{copper chloride} + \text{water} + \text{carbon dioxide}$

Questions & Discussion

• Question: Why was the reaction of an eggshell in acid slower in ethanoic acid than in hydrochloric acid?
• Response: Ethanoic acid has a higher $pH$ (is less acidic/weaker) than hydrochloric acid. A more acidic solution (lower $pH$) reacts more vigorously, which can be observed by more rapid bubbling (fizzing), a faster rise in temperature, or the metal being used up more quickly.
• Question: Why did a reaction between magnesium and hydrochloric acid eventually stop?
• Response: The reaction stops when one of the reactants (either the acid or the magnesium) has been completely used up.
• Question: Why should a $pH$ probe be dipped in distilled water between tests?
• Response: To clean the probe, prevent contamination between different liquids, and ensure an accurate reading by neutralising the probe back to $pH\,7$.
• Question: What happens to the $pH$ of milk over five days at room temperature?
• Response: The $pH$ decreases (goes from approximately $6.5$ to $2.5$), meaning the milk becomes significantly more acidic over time.