Chemistry 1212 Lab Final Exam Complete Questions and Answers

Chemistry 1212 Lab Final Exam Complete Questions and Answers Introductory Lab - CORRECT ANSWER-Purpose: Review of sig figs, slope formula (Y2- Y1/X2-X1); percent error formula ([Accepted-Experimental (/) Accepted] x 100%); rounding, scientific notation, & excel. Procedure: Measured various objects for circumference (C=2πr) and diameter (2r), then produced a graph comparing the two factors. Results: N/A Significant Figure Rules - CORRECT ANSWER-1. All non-zeros are significant. Ex: 12.12 has 4 sig figs. 2. All zeros between non-zeros are significant. Ex: 1203.03 has 6 sig figs. 3. For #'s less than 1: all zeros to the left of the 1st nonzero are NOT significant. Ex: 0. has 6 sig figs. 4. For every # with a decimal, all zeros expressed to the right of a # are significant. Ex: 0.073500 has 5 sig figs. 73500.00 has 7 sig figs. 5. When a # has no decimal, we must assume the significant numbers end when the trailing zeros begin. Ex: 73500 has 3 sig figs. Rounding Rules - CORRECT ANSWER-A) 5 or greater: round UP B) 4 or below: drop remaining digits C) Exactly 5, with no other nonzero #s to the right of it, round UP if the previous digit is odd, but leave the digit as is if it is even. Lewis Structures, Polarity, and Chromatography - CORRECT ANSWER-Purpose: Apply concepts of shape and electronegativity to determine if a molecule is polar or nonpolar; evaluate effects of intermolecular forces and molecule sizes on retention factors in paper chromatography; determine the identity of an unknown by the comparison of retention factors of known compounds. Procedure: On a 12x25cm piece of paper, spread x's about an inch from the bottom of the paper for each amino acid and the unknown. Roll into tube and place into large beaker. Add 25 ml of chromatography solution (without submerging the x's). Cover beaker with foil. Monitor solvent progress for up to 20 mins, allowing liquid to wick up to 2 cm to the top of the paper. Remove paper and draw a line above where the liquid stops, not focusing on straightness. This is the solvent front. Allow 5 mins for solvent evaporation, then spray paper with 1% ninhydrin solution in ethanol. After 3 mins of drying, heat the oven to 130 degrees for 1-2 mins. Measure the distance from the origin to the center of the darkest part of each sample smudge. The unknown should be two smudges.