Describing Chemical Reactions

• Accurate observations of chemical reactions are crucial for scientists.
• Simple descriptions of chemical reactions are sufficient.

Describing Reactions

• Describe the color and state (solid, liquid, gas, solution) of the substances.
• Describe the reactants before the reaction, what happens during the reaction, and the products after the reaction.
• Always note the starting and final colors, using simple color descriptions.
• Observations include smell, hearing, and temperature changes, not just sight.
• Allow reactions enough time, as they may be slow or have secondary changes.

Phrases for Describing Observations

• Colorless solution turns brown.
• Colorless solution becomes cloudy white, forms a white precipitate, or produces a white solid.
• A solid dissolves.
• Bubbles, fizzes, effervescence, or foams appear, varying in speed and intensity.
• Burning with a white light occurs.
• A black solid coating forms.
• A solid melts into a liquid.
• White smoke is produced (fine solid particles).
• A solid ignites or burns.

Auditory Observations

• A squeaky pop sound is made.
• A cracking noise is heard.

Tactile Observations

• The solution gets warmer.
• The solution gets cooler.
• A lot of heat is released.

Acids, Carbonates, and Salts

• Acids have a pH less than 7.
• Dilute lab acids, such as hydrochloric, sulphuric, and nitric acid, are irritants and can inflame skin or eyes.
• Wash off acid spills with plenty of water to prevent burns.
• Concentrated acids are corrosive, reacting with metals and destroying skin tissue.

Universal Indicator and pH Scale

• Universal indicator is a mix of indicators showing solution acidity or alkalinity and its pH.
• Neutral solutions have a pH of 7.
• Acidic solutions have a pH less than 7.
• Alkaline solutions have a pH greater than 7.

Reactions Between Acids and Carbonates

• Carbonates neutralize acids to produce salt, water, and carbon dioxide.
• Adding carbonate to acid typically results in fizzing (carbon dioxide bubbling through limewater, turning it from colorless to milky-white).
• The carbonate dissolves, the temperature rises, and the pH changes.
• General equation: acid + metal carbonate -> salt + water + carbon dioxide

Naming Salts

• Salt names have two parts.
• The first part comes from the metal in the metal carbonate.
• The second part comes from the acid used.
• Salts from hydrochloric acid end in -chloride, and those from sulphuric acid end in -sulphate.
• Example: zinc carbonate + sulfuric acid -> zinc sulfate + water + carbon dioxide

Reactions of Carbonates with Acids Experiment

• Hydrochloric acid is an irritant with low risk, but eye protection is necessary.
• First setup: Place metal carbonates in three test tubes and limewater in a fourth.
• Second setup: Add hydrochloric acid to one test tube with metal carbonate, seal, and observe.
• Identify the gas by using a teat pipette to suck out gas, then suck and squeeze limewater in and out.
• Wash and refill the test tube with limewater. Repeat steps with other metal carbonates.
• Marble chip (calcium carbonate) and sulfuric acid can be used instead of metal carbonates.