Year 9 Chemistry topics 2-4

What is an acid?

An acid is a substance that releases hydrogen ions (H+) into a solution.

Give examples of common acids.

Hydrochloric acid (HCl), acetic acid (CH3COOH), formic acid (CH2O2), nitric acid (HNO3), and sulfuric acid (H2SO4).

What differentiates strong acids from weak acids?

Strong acids have a higher concentration of H+ ions, whereas weak acids have a lower concentration.

Name some strong acids.

Hydrochloric acid, sulfuric acid, and nitric acid.

Name some weak acids.

Ethanoic acid, carbonic acid, and phosphoric acid.

What is a base?

A base is a substance that releases hydroxide ions (OH-) into a solution.

What is an alkali?

A base that is dissolved in water.

Give examples of common bases.

Sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonia (NH3), and calcium hydroxide (Ca(OH)2).

What differentiates strong bases from weak bases?

Strong bases have a higher concentration of OH- ions, whereas weak bases have a lower concentration.

Name some strong bases.

Potassium hydroxide, sodium hydroxide, and barium hydroxide.

Name some weak bases.

Ammonia, calcium carbonate, and sodium carbonate.

What does pH stand for?

pH means 'the power of Hydrogen'.

What is the pH scale range?

The pH scale ranges from 0 to 14.

What does a low pH indicate?

Low pH numbers (less than 7) indicate that substances are acidic.

What does a high pH indicate?

High pH numbers (more than 7) indicate that substances are basic.

What is the pH of a neutral substance?

A substance with a pH of 7 is neutral, meaning it is neither acidic nor basic.

What are acid-base indicators?

Indicators are substances that can tell whether a substance is an acid or a base by changing color.

What is a universal indicator?

A universal indicator is a mixture of indicators that changes color as the strength of an acid or base changes.

What happens in a neutralisation reaction?

An acid and a base react to form water and a salt.

What is an example of a neutralisation reaction in everyday life?

Antacids neutralise stomach acid (HCl) to relieve heartburn.

What are common antacid substances?

Magnesium hydroxide (Mg(OH)2), aluminium hydroxide (Al(OH)3), magnesium carbonate (MgCO3), and calcium carbonate (CaCO3).

How do acids preserve food?

Acids prevent the growth of microorganisms, thus preserving foods like pickles and chutney.

What is the reaction when baking soda (a base) is mixed with an acid?

The reaction produces salt, water, and carbon dioxide, which causes the mixture to rise.

What are synthesis reactions?

Synthesis reactions occur when elements or compounds combine to form more complex products.

What are decomposition reactions?

Decomposition reactions occur when larger compounds break down into two or more smaller compounds or elements.

What are corrosive acids?

Corrosive acids can dissolve metals, damage materials, and burn skin.

How can acid spills be neutralised?

Acid spills can be neutralised using a basic substance, such as sodium bicarbonate.

What is tooth enamel and how is it affected by acids?

Tooth enamel is a hard outer layer that can be dissolved by acids, leading to tooth decay.

What are some ways to prevent tooth decay caused by acids?

Brushing, flossing, and avoiding sugary foods can help prevent tooth decay.

What occurs during a chemical reaction?

Bonds between atoms are broken and new bonds are formed, creating a new arrangement of atoms and at least one new substance.

What are observable changes that indicate a chemical reaction has taken place?

Changes in temperature, color, and the formation of a new product (solid, liquid, or gas).

What are reactants in a chemical reaction?

The original substances you begin with in a chemical reaction.

What are products in a chemical reaction?

The new substances formed during the chemical reaction.

What is the Law of Conservation of Mass?

It states that atoms are neither created nor destroyed in a chemical reaction; they are rearranged.

What does the Law of Constant Proportions state?

A compound always contains the same relative amounts of each element, regardless of how it is formed.

What is an example of the Law of Constant Proportions?

Carbon dioxide (CO₂) always contains a 2:1 ratio of carbon to oxygen.

What is a word equation in chemistry?

A worded description of the molecules in a reaction, without showing quantities or molecular formulas.

What is a balanced chemical equation?

A detailed representation showing the elements and quantities of reactants and products using molecular formulas.

What is the first step in balancing chemical equations?

Determine the reactants and products, and write a word equation.

What is the role of coefficients in balancing chemical equations?

Coefficients multiply all of the atoms in the formula to balance the number of atoms on both sides of the equation.

What symbols indicate the physical states of chemicals in a reaction?

Solid (s), liquid (l), aqueous (aq), and gas (g).

What is the significance of balancing chemical equations?

To ensure that the number of atoms of each element is the same on both sides of the equation, in accordance with the Law of Conservation of Mass.

What is a balanced equation?

An equation where the number of atoms for each element is equal on both sides.

What is an unbalanced equation?

An equation where the number of atoms for each element is not equal on both sides.

What is a coefficient in the context of chemical equations?

A number placed in front of a formula to indicate how many molecules are involved in the reaction.

What are the components of a chemical reaction?

Reactants, products, and the conditions under which the reaction occurs.

What is the importance of understanding chemical symbols?

They are essential for reading and writing chemical reactions accurately.

What is photosynthesis in terms of chemical reactions?

A chemical reaction where carbon dioxide and water are converted into glucose and oxygen using sunlight.

What is the purpose of practicing balancing chemical equations?

To develop skills in ensuring that chemical equations accurately represent the conservation of mass.

How do you check if a chemical equation is balanced?

Count the number of atoms of each element on both sides of the equation.

What is the relationship between reactants and products?

The atoms in the reactants are rearranged to form the products during a chemical reaction.

What is the significance of the fixed ratio in compounds?

It helps scientists understand how atoms bond together to form compounds.

What is the process of rearranging atoms and molecules in a chemical reaction?

Atoms are broken apart from their original bonds and reformed into new substances.

What is the role of observable changes in identifying a chemical reaction?

They provide evidence that a chemical reaction has occurred.