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# CHEM101

### Midterm Exam Review

Questions | Answers |
---|---|

Express the number 0.000000000070 in scientific notation. | 7.0 x 10^-11 Because you moved the decimal point to the right, the sign of the exponent is negative. |

Express the number 5983 in scientific notation. | 5.983 x 10^3 Remember, when the decimal point is moved to the left, the exponent is positive. |

Express the number 0.00034 in scientific notation. | 3.4 x 10^-4 |

Rules for Significant Figures: 1. All nonzero digits are significant. 2. Interior zeros are significant. 3. Trailing zeros that fall after a decimal point are significant. 4. Trailing zeros that fall before a decimal point are significant. | 5. Leading zeros are not significant. They only serve to locate the decimal point. 6. Trailing zeros at the end of a number, but before an implied decimal point, are ambiguous and should be avoided using scientific notation. |

How many significant figures are in: a. 0.0035 b. 1.080 c. 2371 d. 2.97 x 10^5 e. 1 dozen = 12 f. 100.00 g. 100,000 | a. 2 s. fig. b. 4 s. fig. c. 4 s. fig. d. 3 s. fig. e. unlimited s. fig. f. 5 s. fig. g. ambiguous |

Significant Figures in Calculations: In multiplication and division, the result carries the same number of significant figures as the factor with the FEWEST SIGNIFICANT FIGURES. | In addition and subtraction, the result has the same number of decimal places as the quantity with the FEWEST DECIMAL PLACES. |

Perform each calculation to the correct number of significant figures. a. 1.01 x 0.12 x 53.51 / 96 b. 56.55 x 0.920 / 34.2585 | a. 0.067556 = 0.068 (0.12 and 96 both have 2 sig. fig.) b. 1.51863 = 1.52 (0.920 has 3 sig. fig.) |

Perform each calculation to the correct number of significant figures. a. 0.987 + 125.1 - 1.22 b. 0.765 - 3.449 - 5.98 | a. 124.867 = 124.8 (125.1 has the fewest decimal places) b. -8.664 = -8.66 (-5.98 has the fewest decimal places) |

Perform the calculation to the correct number of significant figures. 6.78 x 5.903 x (5.489 - 5.01) | 19.1707 = 19 (Parentheses first and follow the subtraction rule to mark 0.479 to two decimal places because 5.01 has only two. Then perform the multiplication and round the answer to two sig. fig. because 0.47(9) has two. |

Perform the calculation to the correct number of significant figures. 19.667 - (5.4 x 0.916) | 14.7206 = 14.7 (Parentheses first. The number with the least number of sig. fig. within the parentheses (5.4) has two, so mark the answer to two sig. fig. Then perform the subtraction and round the answer to one decimal place, (5.4) has one. |

Scientific measurements are based on the metric system. These measurements are called SI units. length = meter = m mass = kilogram = kg time = second = s temperature* = kelvin = K | |

Common units and their equivalents: 1 kilometer = 0.6214 mile 1 meter = 39.37 inches = 1.094 yards 1 foot = 30.48 centimeters 1 inch = 2.54 centimeters | 1 kilogram = 2.205 pounds 1 pound = 453.29 grams 1 ounce = 28.35 grams |

Common units and their equivalents: 1 liter = 1000 milliliters = 1000 cubic centimeters 1 liter = 1.057 quarts 1 US gallon = 3.785 liters | |

Converting Between Units: information given x conversion factor(s) = information sought given unit x desired unit/given unit = desired unit | |

Convert 7.8 km to miles. | 7.8 km x 0.6214 mi/1 km = 4.84692 mi = 4.8 mi (km cancel out, mi carry over as the desired unit) |

Convert 0.825 m to millimeters. | 0.825 m x 1 mm/10^-3 m = 825 mm (m cancel out, mm carry over as the desired unit) |

Find the density of a ring with a mass of 5.84 g which displaces 0.556 cubic centimeters of water. | d = 5.84 g/0.556 cm3 d = 10.5 g/cm3 |

The gasoline in an automobile gas tank has a mass of 60.0 kg and a density of 0.752 g/cm3. What is its volume in cm3? | 60.0 kg x 1000 g/1 kg x 1 cm^3/0.752 g = 7.98 x 10^4 cm3 |

A chemist needs a 23.5 kg sample of ethanol for a large-scale reaction. What volume in liters of ethanol should the chemist use? The density of ethanol is 0.789 g/cm3. | 23.5 kg x 1000 g/1 kg x 1 cm3/0.789 g x 1 mL/1 cm3 x 1 L/1000 mL = 29.7845 L = 29.8 L |

Express the number 323,000,000 in scientific notation. | 3.23 x 10^8 Because you move the decimal point to the left, the sign of the exponent is positive. |

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