pH Levels and Chemical Reactions Review

Identification and Classification of Acids, Bases, and Neutral Substances

The following substances were tested for their pH levels to determine whether they are acidic, basic, or neutral. A substance's pH level indicates its chemical nature on a scale where $7$ is neutral, values below $7$ are acidic, and values above $7$ are basic.

1. Tomato Juice: This substance has a pH level of $4$. It is classified as an ACID.

2. Blood: This substance has a pH level of $8$. It is classified as a BASE.

3. Gastric Juice (Stomach): This substance has a pH level of $1$. It is classified as an ACID. It is associated with the bolus, stomach, and small intestine.

4. Water: This substance has a pH level of $7$. It is classified as NEUTRAL.

5. RAM Baking Soda: Used for baking, cleaning, and deodorizing, this product has a net weight of $500\,g$ ($17.6\,oz$). It has a pH level of $9$ and is classified as a BASE.

6. Bath & Body Works Mango Papaya Paradise Gentle & Clean Foaming Hand Soap (Savon Moussant Pour Les Mains Doux Et Net): This product has a volume of $e259\,ml$ ($8.75\,fl\,oz$). It has a pH level of $10$ and is classified as a BASE.

7. Datu Puti Vinegar (Sarap-Asim): This product contains $5\,\%$ acidity. It has a net content of $33.81\,fl\,oz$ ($1\,L$). It has a pH level of $3$ and is classified as an ACID.

8. Apollo Strong Ammonia Solution: Distributed by Philusa Corporation and intended for external use only, this substance has a pH level of $11$. It is classified as a BASE.

9. Black Coffee: This substance has a pH level of $5$. It is classified as an ACID.

10. Zonrox Original Bleach: This is a 6-in-1 multi-purpose bleach for home and laundry that claims to be $99.9\,\%$ "Antiboxc." It is marketed to "kits disease-cousing genres and vases," whiten, remove stains, deodorize, and shorten cleaning time. It has a pH level of $12$ and is classified as a BASE.

Fundamental Principles of Chemical Reactions

A chemical reaction is a process where substances (reactants) transform into new substances (products) with different properties. During this process, the particles of the substances rearrange to form new products. Atoms are not created or destroyed in a reaction; they are merely rearranged.

Reactants are defined as the substances that are mixed together. Products are defined as the new substances resulting from the chemical reaction among the reactants. The Law of Conservation of Mass states that the total mass of reactants must equal the total mass of products. As an example, a gold necklace weighing $20\,g$ that breaks into 50 tiny pieces or is melted into a ring will still weigh exactly $20\,g$.

Evidence of a chemical reaction include:

• Color change
• Evolution of gas (bubbles)
• Formation of a precipitate (solid)
• Change in temperature (release or absorption of heat)
• Odor change

Short Review Questions and Answers

QUESTION 1: Why does iron rust? ANSWER: Iron rusts because it reacts with oxygen and moisture in the air. This chemical reaction forms a new substance called rust (iron oxide). Rusting is an example of a chemical change because the iron changes into a different material.

QUESTION 2: Why does food burn when cooked too long? ANSWER: Food burns when it is exposed to too much heat for a long time. The heat causes chemical reactions that change the food's color, smell, and taste, producing burnt substances. This is also a chemical change because new substances are formed and the change cannot easily be reversed.

Type 1: Combination (Synthesis) Reactions

A combination reaction occurs when two or more substances (smaller substances) join together to form exactly one new product. The general formula for this reaction is $A + B \rightarrow AB$.

Common examples include:

• Rusting of iron (Oxidation): $4Fe + 3O_2 \rightarrow 2Fe_2O_3$
• Heating of Magnesium: $2Mg + O_2 \rightarrow 2MgO$ (Magnesium Oxide is used in antacids and laxatives)
• Formation of Water: $2H_2 + O_2 \rightarrow 2H_2O$
• Photosynthesis: $6CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2$

Additional balanced combination equations include:

• Formation of hydrogen chloride: $H_2 + Cl_2 \rightarrow 2HCl$
• Formation of hydrogen bromide: $H_2 + Br_2 \rightarrow 2HBr$
• Formation of units like sulfur trioxide: $2SO_2 + O_2 \rightarrow 2SO_3$
• Formation of phosphorus pentoxide: $4P + 5O_2 \rightarrow 2P_2O_5$
• Formation of potassium chloride: $2K + Cl_2 \rightarrow 2KCl$
• Formation of lithium oxide: $4Li + O_2 \rightarrow 2Li_2O$
• Formation of calcium sulfide: $Ca + S \rightarrow CaS$
• Formation of zinc oxide: $2Zn + O_2 \rightarrow 2ZnO$
• Formation of copper(II) oxide: $2Cu + O_2 \rightarrow 2CuO$
• Formation of magnesium sulfide: $Mg + S \rightarrow MgS$
• Formation of sodium oxide: $4Na + O_2 \rightarrow 2Na_2O$
• Formation of iron sulfide: $Fe + S \rightarrow FeS$
• Formation of nitrogen monoxide: $N_2 + O_2 \rightarrow 2NO$
• Formation of carbon monoxide: $2C + O_2 \rightarrow 2CO$

Type 2: Decomposition Reactions

A decomposition reaction occurs when one compound breaks apart into two or more simpler substances. The general formula is $AB \rightarrow A + B$.

Examples of decomposition include:

• Electrolysis of water: $2H_2O \rightarrow 2H_2 + O_2$
• Breakdown of hydrogen peroxide: $2H_2O_2 \rightarrow 2H_2O + O_2$
• Heating of "Baking sosa" (Baking Soda): $2NaHCO_3 \rightarrow Na_2CO_3 + H_2O + CO_2$
• Cell Respiration: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy (ATP)}$
• Food Spoilage: Food breaks down over time into simpler substances, causing changes in smell, color, and texture.

Type 3: Single Replacement Reactions

A single replacement (or single displacement) reaction occurs when one element replaces another element in a compound. The general formula is $AB + C \rightarrow AC + B$ or $AB + X \rightarrow AX + B$.

Key principles and examples:

• Reactivity Rule: Fluorine ($F$) can replace Bromine ($Br$) because it is more reactive. For example, $F_2 + 2NaBr \rightarrow 2NaF + Br_2$. This reaction cannot be reversed because bromine is "weaker" than fluorine.
• Zinc in Hydrochloric Acid: $Zn + 2HCl \rightarrow ZnCl_2 + H_2$
• Iron Nail in Copper Sulfate: $Fe + CuSO_4 \rightarrow FeSO_4 + Cu$
• Magnesium and Hydrochloric Acid: $Mg + 2HCl \rightarrow MgCl_2 + H_2$
• Copper and Silver Nitrate: $Cu + 2AgNO_3 \rightarrow Cu(NO_3)_2 + 2Ag$
• Aluminum in Copper Chloride: $2Al + 3CuCl_2 \rightarrow 2AlCl_3 + 3Cu$
• Chlorine and Potassium Bromide: $Cl_2 + 2KBr \rightarrow 2KCl + Br_2$
• Bromine and Potassium Iodide: $Br_2 + 2KI \rightarrow 2KBr + I_2$
• Calcium and Water: $Ca + 2H_2O \rightarrow Ca(OH)_2 + H_2$
• Sodium and Water: $2Na + 2H_2O \rightarrow 2NaOH + H_2$
• Lead and Copper(II) Nitrate: $Pb + Cu(NO_3)_2 \rightarrow Pb(NO_3)_2 + Cu$
• Acids on Metals: The metal replaces hydrogen in the acid to produce a salt and hydrogen gas ($H_2$).
• Battery Reactions: Reactions in batteries involve elements replacing others to produce electricity.

Type 4: Double Replacement Reactions

A double replacement (or double displacement) reaction occurs when two compounds exchange parts (ions) to form two new compounds. The general formula is $AB + CD \rightarrow AC + BD$ or $AB + XY \rightarrow AX + BY$.

Examples include:

• Silver Nitrate and Sodium Chloride: $AgNO_3 + NaCl \rightarrow AgCl + NaNO_3$
• Barium Chloride and Sodium Sulfate: $BaCl_2 + Na_2SO_4 \rightarrow BaS O_4 + 2NaCl$
• Vinegar and Baking Soda: $CH_3COOH + NaHCO_3 \rightarrow CH_3COONa + H_2O + CO_2$ (Produces sodium acetate, carbon dioxide, and water)
• Soap Scum Formation: $2C_{17}H_{35}COONa + CaCl_2 \rightarrow (C_{17}H_{35}COO)_2Ca + 2NaCl$
• Curding of Milk: Milk proteins react with citric acid (from lemon juice) to form curd (precipitate) and whey (fluid).
• Precipitation: Many of these reactions form a solid precipitate as seen in Silver chloride ($AgCl$) or Lead(II) iodide ($PbI_2$) formation.

Balanced examples for practice:

• $Pb(NO_3)_2 + 2KI \rightarrow PbI_2 + 2KNO_3$
• $CaCl_2 + Na_2CO_3 \rightarrow CaCO_3 + 2NaCl$
• $HCl + NaOH \rightarrow NaCl + H_2O$
• $H_2SO_4 + 2KOH \rightarrow K_2SO_4 + 2H_2O$
• $CuSO_4 + 2NaOH \rightarrow Cu(OH)_2 + Na_2SO_4$
• $FeCl_3 + 3NaOH \rightarrow Fe(OH)_3 + 3NaCl$
• $MgCl_2 + 2AgNO_3 \rightarrow 2AgCl + Mg(NO_3)_2$
• $2Na_3PO_4 + 3CaCl_2 \rightarrow Ca_3(PO_4)_2 + 6NaCl$

Type 5: Combustion Reactions

A combustion reaction is a process where a fuel reacts with oxygen to produce carbon dioxide ($CO_2$), water ($H_2O$), and energy in the form of heat and light. The fuel must react with $O_2$.

Specific examples include:

• Burning Methane (Natural Gas): $CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O + \text{Energy}$
• Burning Propane (LPG): $C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O + \text{Energy}$
• Burning Ethanol: $C_2H_5OH + 3O_2 \rightarrow 2CO_2 + 3H_2O + \text{Energy}$
• Burning Wood (simplified): $C + O_2 \rightarrow CO_2 + \text{Energy}$. Wood burning also produces ash and water vapor.
• Candle Burning: Wax reacts with oxygen to produce heat, light, $CO_2$, and water vapor.

Type 6: Acid-Base (Neutralization) Reactions

An acid-base neutralization reaction is a special type of double displacement reaction where an acid reacts with a base to produce a salt and water. This reaction reduces the acidic and basic properties of the reactants. The $H^+$ of the acid reacts with the $OH^-$ of the base to form water ($H_2O$).

Examples include:

• Hydrochloric acid and Sodium hydroxide: $HCl + NaOH \rightarrow NaCl + H_2O$
• Phosphoric acid and Calcium hydroxide: $2H_3PO_4 + 3Ca(OH)_2 \rightarrow 6H_2O + Ca_3(PO_4)_2$
• Hydrochloric acid and Potassium hydroxide: $HCl + KOH \rightarrow H_2O + KCl$
• Sulfuric acid and Calcium hydroxide: $H_2SO_4 + Ca(OH)_2 \rightarrow CaSO_4 + 2H_2O$
• Hydrofluoric acid and Calcium oxide: $HF + CaO \rightarrow \text{Fluoride} + \text{Hydronium} + \dots$
• Hydrobromic acid and Ammonia: $HBr + NH_3 \rightarrow Br^- + NH_4^+$