【Inorganic Chemistry】 Mastering the Common Test! Study Notes to Turn Memorization into Your Weapon
Hello everyone! Welcome to the "Inorganic Substances" section of chemistry. You might be feeling that "Inorganic chemistry is just endless memorization..." But in reality, inorganic substances follow clear rules and color patterns. If you grasp those, this will turn into a "delicious" topic—a surefire source of points for the Common Test!
It might feel difficult at first, but don't worry. You'll encounter many topics closely related to your everyday life, like aluminum cans, bleach, and batteries. Let's learn while having fun!
---1. Non-metal Elements: Everyday Gases and Substance Properties
Let's start with non-metal elements, which are abundant on the right side of the periodic table. In the Common Test, "color," "odor," and "properties" are frequently tested.
① Halogens (Group 17: F, Cl, Br, I)
All halogens are toxic and highly reactive.
【How to remember the colors】
・Fluorine (F\(_2\)): Pale yellow (gas)
・Chlorine (Cl\(_2\)): Yellow-green (gas)
・Bromine (Br\(_2\)): Red-brown (liquid! *The only non-metal liquid at room temperature)
・Iodine (I\(_2\)): Black-purple (solid, exhibits sublimation)
Key point: The color deepens as you go down the group, and since the molecular weight increases, they change from gas → liquid → solid.
② Nitrogen and Phosphorus (Group 15: N, P)
Important compounds of nitrogen are ammonia and nitric acid.
Trivia: The industrial production method for ammonia is the Haber-Bosch process. It synthesizes ammonia from nitrogen and hydrogen using triiron tetroxide as a catalyst.
Phosphorus has "allotropes":
・White phosphorus: Highly toxic, spontaneously ignites in air (store under water!).
・Red phosphorus: Used on the striking surface of matchboxes. Low toxicity.
Common mistake: "Store white phosphorus in the air" is WRONG! It will ignite, so keep it underwater.
③ Carbon and Silicon (Group 14: C, Si)
Silicon (Si) is famous as a material for semiconductors. Silica gel: A desiccant made from processed silicon dioxide (SiO\(_2\)). It has many hydroxy groups (-OH) on its surface that capture water molecules.
【Summary of this section】 ・Memorize the halogen colors as a set! ・Store white phosphorus underwater! ・The Haber-Bosch process is for making ammonia!
---2. Typical Metallic Elements: The Metals Around Us
Next are the typical metals located on the left and bottom-right of the periodic table. Ion reactions and precipitation are crucial here!
① Alkali Metals (Group 1: Li, Na, K...)
These are extremely reactive and react with water to release hydrogen. Flame reactions are super important! 【How to remember flame reactions】 "Li-A-Car (Li: red), Na (Na: yellow), Ki (K: red-purple), K-mura (Cu: green), Doryoku (Sr: crimson), Kariru-to (Ca: orange), Surumo-kurenai (Ba: yellow-green)" With that, you're all set!
② Aluminum (Group 13: Al)
Aluminum is an amphoteric element. Remember them as "Aa-sunnari" (Al, Zn, Sn, Pb).
They dissolve in both acids and strong bases, releasing hydrogen.
Industrial process (Hall-Héroult process):
Aluminum oxide (alumina) is dissolved in cryolite and subjected to molten salt electrolysis.
It uses so much electricity that it's often called "canned electricity."
③ Zinc, Tin, and Lead
These are also amphoteric elements. Be especially careful with lead (Pb), as it has the unique property of being difficult to dissolve in hydrochloric or sulfuric acid (because an insoluble salt forms on the surface, stopping the reaction).
【Summary of this section】 ・Memorize flame reactions by rhythm! ・Amphoteric elements (Al, Zn, Sn, Pb) dissolve in both acids and bases! ・"Cryolite" is required for the production of aluminum!
---3. Transition Elements: The Colorful World of Ions
These elements are in the middle of the periodic table (Groups 3–11). This is the hardest part for "color memorization," but treat it like a puzzle and enjoy it!
① Characteristics
・They have multiple oxidation states (e.g., Fe\(^{2+}\) and Fe\(^{3+}\)). ・The ions are often colored. ・They easily form complex ions.
② Iron (Fe)
・Fe\(^{2+}\): Pale green ・Fe\(^{3+}\): Yellow-brown The color changes when you add reagents like potassium hexacyanoferrate(II) are a super frequent topic in the Common Test! Key point: When potassium thiocyanate (KSCN) is added to Fe\(^{3+}\), it turns into a blood-red solution. The name sounds scary, but the color is vibrant!
③ Copper (Cu)
・Cu\(^{2+}\): Blue ・Adding a small amount of aqueous ammonia to copper produces a pale blue precipitate. ・Adding an excess of ammonia results in a deep blue solution (tetraamminecopper(II) ion). This "precipitate with a little, dissolves with excess" pattern is common in transition metals.
④ Silver (Ag)
Silver ions Ag\(^+\) react with halide ions to form precipitates. ・AgCl: White ・AgBr: Pale yellow (used in photographic film) ・AgI: Yellow Trivia: Only AgF is water-soluble! Remember it as "Silver halides don't dissolve, but fluorine is the exception."
【Summary of this section】 ・Transition elements are colorful! ・Iron ion reactions are all about the combination with reagents! ・Excess ammonia with copper results in "deep blue"!
---4. Industrial Processes and Ion Separation: Inorganic Summary
Finally, let's review the frequently appearing industrial processes and "systematic separation," which involves separating ions that have been mixed together.
① The Three Major Industrial Processes
1. Contact process: Produces sulfuric acid (H\(_2\)SO\(_4\)). The catalyst is vanadium(V) oxide. 2. Ostwald process: Produces nitric acid (HNO\(_3\)). The catalyst is platinum (Pt). It involves the oxidation of ammonia. 3. Ammonia-soda process (Solvay process): Produces sodium carbonate (Na\(_2\)CO\(_3\)). Tip: Instead of memorizing the reaction equations by heart, first match "what is used" with "what is produced."
② Systematic Separation of Ions (Tips for success)
This is the operation of extracting ions one by one from an aqueous solution containing a mixture of many different ions.
・What precipitates by adding hydrochloric acid? → Ag\(^+\), Pb\(^{2+}\) (chloride precipitation)
・What precipitates by passing hydrogen sulfide (H\(_2\)S) in an acidic solution? → Cu\(^{2+}\), Ag\(^+\) (those with low ionization tendency)
・What precipitates by passing H\(_2\)S in a basic solution? → Zn\(^{2+}\), Fe\(^{2+}\), Ni\(^{2+}\)
Advice: The best way to master this is to write out a "precipitation table" yourself at least once. Be especially careful with S\(^{2-}\) (sulfide ions), as the partner that precipitates changes depending on the "solution property" (acidic or basic)!
【Summary of this section】 ・Sulfuric acid = Contact process, Nitric acid = Ostwald process! ・Systematic separation is like a chase—"who drops out when I add this?"
---Closing
Great job finishing your study of inorganic substances! It may seem like there is a lot to memorize, but linking "visual images of colors" with "reasons for reactions (acid/base, redox, etc.)" will drastically improve your retention.
Even if the Common Test presents an experimental setup you've never seen before, the knowledge used is always the basics you've learned. Start by perfecting the colors and names of the representative substances in your textbook!
Take it one step at a time, and you will definitely make this a subject you excel in. Good luck!