Chem 113 Recitation Week 1

Chem 113 Recitation – Week 1 – Chapter 1 Review Scientific Notation Everyone should use the same notation on their assignments. Please don’t use E, or you may lose points. Right: 2x10-6 Wrong: 2E-6,2E-6, 2x10(-6), anything that isn’t “right”

Significant Figures Remember these rules when determining sig figs: 1. Any digit that is nonzero is significant. 2. Zeros between nonzero digits are significant. 3. Zeros to the left of the first nonzero digit are not significant. 4. If a number is greater than 1, then all of the zeros to the right of the decimal are significant. If a number is less than 1, then only the zeros that are at the end of the number and the zeros that are between nonzero digits are significant. 5. Trailing zeros can either be significant or not. To simplify grading, please tell us how many sig figs you are assuming, and your answer will be graded accordingly.

Sig figs in calculations: 1. Addition and subtraction: the answer should have no more decimal places that the least of the original numbers. 2. Multiplication and division: the answer should have the same number of sig figs as the original number with the smallest sig figs. 3. Exact numbers do not affect the number of sig figs in your answer. Examples: A. Convert the following to correct scientific notation: 1) 131,000.0 2) 0.077x10-9 3) 0.00380 4) 7500x10-3 1) 1.310000x105 2) 7.7x10-11 3) 3.80x10-3 4) 7.5

B. Carry out the following calculations: 1) (2.795 m X 3.10 m)/6.48 m 1.34 m 2) (2.420 g + 15.6 g)/4.8 g 3.8 g 3) ((1.07x10-4)2(2.6x10-3))/((8.35x10-5)(1.48x10-2)3) 0.11

C. The radius of a barium atom is 2.22x10-10 m. What is the radius in angstroms? (2x10-10 m)(1 Angstrom/10-10 m) = 2.22 Angstrom

D. The average density of the Earth is 5.52 g/cm3. What is the density in lb/ft3? 5.52 g/cm3(1 lb/453. 6g)(2.54 cm/1 in)3(12 in/1 ft)3 = 345 lb/ft3 General Review of Chapter 1: - Qualitative vs. Quantitative Qualitative describes general observations while Quantitative includes numbers that were obtained through measurement

- Homogeneous vs. Heterogeneous Homogeneous refers to a mixture that contains only one phase, or a solution. Heterogeneous refers to a mixture that contains more than one phase, such as a colloid or a suspension

- Substance vs. Element vs. Compound A substance is a form of matter that has definite proportions and distinct properties. An element is a substance that cannot be broken down further by chemical means. A compound is a mixture of elements that have come together in definite, unchanging proportions to for a new substance.

- Properties: Chemical vs. Physical, Extensive vs. Intensive, Macroscopic vs. Microscopic A chemical property is one that we can only observe by carrying out a chemical reaction, whereas a physical property can be observed without changing the composition of a substance. An extensive property is one that depends on the size of your sample (mass and volume) where an intensive property will be the same for all samples, regardless of size (density). A macroscopic property is one that can be viewed with the naked eye, where an microscopic property refers to the atomic level and can only be viewed with a microscope.

- Mass vs. Weight Mass describes the amount of matter a sample has. Weight is the pull of gravity on that specific mass.

- Accuracy vs. Precision Accuracy describes how close your result is to the known value, while precision describes how close your results are to one another.