Question

You will analyze four substances in this lab. Based on their chemical formulas and what you already know about covalent and ionic compounds, make a prediction for each compound.

Oil, which is built from the nonmetals hydrogen, carbon, and oxygen:
Cornstarch, a carbohydrate consisting of hydrogen, carbon, and oxygen:
Sodium chloride (table salt), whose formula is NaCl:
Sodium bicarbonate (sodium bicarbonate), whose formula is NaHCO3:

Answer 1

Oil (made of C, H, O)
- Prediction: predominantly covalent (molecular) and largely nonpolar.
- Rationale: composed of long hydrocarbon chains (triglycerides) with only a few polar C–O bonds; no metal present so atoms are joined by covalent bonds. Expect it to be hydrophobic (insoluble in water), not conduct electricity, and be liquid/low-melting compared with ionic solids.

Cornstarch (a carbohydrate of C, H, O)
- Prediction: covalent (a large polymeric/molecular substance).
- Rationale: starch is a polysaccharide (glucose units linked by covalent glycosidic bonds). The many −OH groups make it able to interact with water (swelling/gel formation) but it is not an ionic salt. Expect it to form suspensions/gels in water (not freely conducting) and to decompose rather than have a sharp ionic-type melting point.

Sodium chloride (NaCl)
- Prediction: ionic compound.
- Rationale: contains a metal (Na) and a nonmetal (Cl), so it exists as Na+ and Cl− in a crystalline lattice. Expect high melting/boiling points, brittleness, good solubility in water, and electrical conductivity only when molten or dissolved (not as a dry solid).

Sodium bicarbonate (NaHCO3)
- Prediction: ionic lattice of Na+ and the polyatomic HCO3− (the bicarbonate ion).
- Rationale: Na is a metal and HCO3− is a covalently bonded polyatomic anion, so the solid is an ionic salt. Expect it to dissolve in water (giving Na+ and HCO3− and conducting in solution) and to show typical salt behavior (and to undergo decomposition on strong heating).