Grade 8 Unit 1: Acids, Bases, and Chemical Reactions

Flashcards covering key concepts from Grade 8 Science Unit 1 on acids, bases, chemical reactions, neutralization, dilution, combustion, hydrocarbons, and lab testing.

What occurs during a neutralization reaction between an acid and a base at the ionic level?

The acid releases $H^+$ ions and the base releases $OH^-$ ions, which combine to form water ($H_2O$), while the remaining ions join to form a salt.

What is the general equation and an example word equation for Reaction Type 1 (Acid + Base)?

General equation: $\text{acid} + \text{base} \rightarrow \text{salt} + \text{water}$. Example word equation: $\text{hydrochloric acid} + \text{sodium hydroxide} \rightarrow \text{sodium chloride} + \text{water}$.

What products are formed when an acid reacts with a metal carbonate (Reaction Type 2)?

A salt, carbon dioxide, and water ($\text{acid} + \text{metal carbonate} \rightarrow \text{salt} + \text{carbon dioxide} + \text{water}$).

What is the chemical equation for the neutralization reaction between sulfuric acid and copper oxide (Reaction Type 3)?

$$H_2SO_4(aq) + CuO(s) \rightarrow CuSO_4(aq) + H_2O(l)$$

What is the general equation for a reaction between a metal and an acid (Reaction Type 4), and is it a neutralization reaction?

$\text{metal} + \text{acid} \rightarrow \text{salt} + \text{hydrogen}$. This is not a neutralization reaction.

What are the products of a combustion reaction between a hydrocarbon and oxygen (Reaction Type 5)?

Carbon dioxide and water ($\text{hydrocarbon} + \text{oxygen} \rightarrow \text{carbon dioxide} + \text{water}$).

How do hydrochloric acid, nitric acid, and sulfuric acid determine the specific type of salt formed in a reaction?

Hydrochloric acid forms chloride salts, nitric acid forms nitrate salts, and sulfuric acid forms sulfate salts.

How does dilution affect the strength and pH of an acid?

Dilution increases the volume in which ions are dispersed to reduce concentration, but it does NOT change the strength of the acid. It moves the pH closer to 7, but will never reach 7 or go over 7.

What is the distinction between acid strength and acid concentration?

Acid strength depends on how completely the acid dissociates into $H^+$ ions in water, whereas concentration refers to the amount of acid solute dispersed in a given volume of solution.

What three components make up the fire triangle required for combustion?

Fuel, Oxygen, and Heat.

What mnemonic is used to remember the seven diatomic elements, and what are their chemical formulas?

"I Bring Cookies For Our New Home": Iodine ($I_2$), Bromine ($Br_2$), Chlorine ($Cl_2$), Fluorine ($F_2$), Oxygen ($O_2$), Nitrogen ($N_2$), and Hydrogen ($H_2$).

How do you perform the laboratory test for hydrogen gas, and what indicates a positive result?

Place a lighted wooden splint near the mouth of a test tube containing the gas; a positive test produces a distinctive "squeaky pop" sound.

How is limewater prepared and used to test for the presence of carbon dioxide gas?

Dissolve about $0.1\,g$ of calcium hydroxide (slaked lime) in $50\,mL$ of water and filter it to obtain clear limewater. Blowing carbon dioxide into the filtrate turns it milky or cloudy.

What is combustion, and what forms of energy are released during the process?

Combustion is the rapid chemical combination of a substance with oxygen, releasing energy in the forms of heat and light.

Why does a flame burn more brightly in pure oxygen than in air?

Air contains only $21\%$ oxygen (which is highly flammable) and is mostly non-flammable nitrogen, whereas pure oxygen provides a higher concentration of reactant.

What are the molecular formulas for the first four alkanes (methane, ethane, propane, and butane)?

Methane ($CH_4$), Ethane ($C_2H_6$), Propane ($C_3H_8$), and Butane ($C_4H_{10}$).

What are the primary uses of propane, butane, and hexane according to the lecture notes?

Propane is used for heating and cooking; butane is used in lighters and aerosol cans; hexane is used to produce glue for shoes and leather products.

What acid is present in the human stomach, and what active substance in antacids neutralizes it?

Stomach acid contains hydrochloric acid ($HCl$) with a pH of 1.5; antacids contain an alkali such as calcium carbonate ($CaCO_3$) with a pH of 11.

What is the correct safety rule when mixing acids with water, and why?

Always add the acid to the water (never water to acid) because the solution can generate enough heat to boil and splash.

According to the pH scale reference chart, what are the pH values of gastric acid, black coffee, distilled water, and bleach?

Gastric acid has a pH of 1, black coffee has a pH of 5, distilled water has a pH of 7, and bleach has a pH of 13.