CHM 1025 Exam 1

Definition of Chemical and Physical change.

*physical changes* because they do not affect the composition of the substance. In each state we still have water (H2O), not some other substance. chemical change because water (consisting of H2O molecules) has changed into different substances: hydrogen (containing H2 molecules) and oxygen (containing O2 molecules).

Examples of pure substances.

*pure substance*, on the other hand, will always have the same composition. Pure substances are either elements or compounds. For example, pure water is a compound containing individual H2O molecules. However, as we find it in nature, liquid water always contains other substances in addition to pure water—it is a mixture.

There are two Metric conversions.

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Know how to express a number in scientific notation.

595mg > .595g > 5.95 x 10^-1g

Homogeneous and Heterogeneous mixtures.

A *homogeneous mixture* is the same throughout. For example, when we dissolve some salt in water and stir well, all regions of the resulting mixture have the same properties. A homogeneous mixture is also called a *solution*. *heterogeneous mixture* contains regions that have different properties from those of other regions. For example, when we pour sand into water, the resulting mixture has one region containing water and another, very different region containing mostly sand

Two density problems

Pages 69 & 70 # 17 - 29 Density = mass/volume

Significant Figures - 4 questions.

Rules. 1. All non-zero numbers are significant. 2. Zeros between non zero digits are significant 3. Zeros at the beginning of a number are not significant 4. Zeros at the end of a number are only significant if the number has a decimal point. 5. Exact numbers have unlimited number of significant figures. Rounding- Discarding non significant figures For multiplication and division, look at all the numbers invlovled in the calculations and find the number having the fewest number of significant figures. Round that answer to that many significant figures. For addition and subtraction, all the numbers including the answer have to contribute to the same decimal place. Discard by rounding all other figures after computation During a multistep computation round at the very end of the calculations. Denote with a dash at the significant figures after each of the computations.

Know how to convert from Centigrade to Fahrenheit and from Fahrenheit to Centigrade.

Tf=1.8Tc+32 K=273+C All you need to know

Definition of a compound.

The atoms of certain elements have special affinities for each other. They bind together in special ways to form *compounds*, substances that have the same composition no matter where we find them. Because compounds are made of elements, they can be broken down into elements through chemical changes.

Know the most commonly used Metric prefixes.

kilo k 1000 103 deci d 0.1 101 centi c 0.01 102 milli m 0.001 103 micro m 0.000001 106 nano n 0.000000001 109 km 10^3 m 10 dm 10^-1 cm 10^-2 mm 10^-3 um 10^-6 nm 10^-9