SK015 Pre-Lab 1 Determination Formula Unit of A Compound

Which definition best to describe a compound?

• A group of atoms bonded by metallic bonds

• A pure substance composed of two or more elements chemically combined in a fixed ratio

• A mixture of two or more elements physically combined.

• An element with multiple isotopes

What does the term formula unit refers to?

• The smallest ratio of elements (or ion) in an ionic compound

• A mole of a compound

• An element with multiple isotopes

• A mixture of two or more elements physically combined

Which of the following best describes an empirical formula?

• Shows actual number of atoms in a molecule

• Only applies to gases

• Shows the simplest whole-number ratio of atoms in a compound

• Refers to the mass ratio of elements

The molecular formula (MF) of a compound is always:

• Equal to or a multiple of the empirical formula

• Based on melting point

• Irrelevant for ionic compounds

• Less than its empirical formula

Which of the following is a safety steps in this experiment?

• Always add water to acid

• Heat the compound until it melts

• Handle hot equipment with tongs

• Use broken glassware if cleaned

Why must the apparatus be dried completely before weighing?

• To remove excess acid

• To prevent water from affecting the mass

• To remove oxygen

• To dissolve the compound

Why should the solid compound not be heated to its melting point (or heated until melt)?

• It becomes more reactive

• It bonds with air molecules

• The experiment requires a liquid phase

• It may vaporize or decompose and altering the mass

Why is the solid product obtained must be reheated, cooled, and reweighed?

• To allow time for settling

• To ensure consistent mass for accurate measurement

• To ensure complete combustion

• To check if melting occurred

After heating is done, why is it important to cool the crucible before weighing solid product?

• To allow hydrogen to escape freely

• To prevent zinc from melting

• To avoid errors from convection currents of hot apparatus

• To remove water vapor completely

What is the purpose of using a crucible with a lid in this experiment?

• To retain heat, reduce loss of sample and prevent absorption of moisture

• To allow oxygen in freely and absorption of moisture

• To prevent contamination from environment

• To measure pressure of gas released from reaction