Practice questions

Ammonia

Ammonia is a basic gas. Damp red litmus turns blue. The paper must be damp: the gas needs water to form OH- before the dye can change. Dry litmus shows no change, so the result is uncertain.

Carbohydrates As Fuel

Carbohydrates are organic compounds that serve as a major source of chemical energy for living organisms.

Carbon Dioxide

In the lab, CO2 is made from HCl + marble chips (CaCO3) -> CaCl2 + CO2 + H2O. Limewater is aqueous Ca(OH)2. The gas turns limewater milky because solid CaCO3 forms. That test distinguishes CO2 from O2, which does not milk limewater.

Choosing a Method

Choose a separation method by the difference you can use: size, mass, density, magnetism, volatility, or solubility. Gold panning uses density: dense gold stays while lighter sand washes away. Famous gold rushes in the 1800s used that idea.

Distillation