Chemistry Semester 1 Review!!! Analyzing Data 1. Describe the different parts of a scientific study. a. Hypothesis: educated guess to answer a question or solve a problem b. Independent Variable: the variable being tested or changed c. Dependent Variable: the variable that changes based on the change in the independent variable 2. Explain why experiments are only valid if the experiment is conducted MANY times before the scientific community accepts the findings of a study. The findings are only valid if the experiment is conducted many times by multiple experiments and verified that correctly describes a natural phenomenon. 3. Describe the difference between a theory and a law. A theory is well-established and accepted as true by one or more hypotheses and it is verified that correctly describes a natural phenomenon. A law is the same. 4. When researching scientific issues, why is it best to gather information from multiple sources? To obtain accurate, non-biased, valid information. Measure the following using the appropriate number of significant digits. a. 62.7 mL b. 2.69 cm c. 31.0 °C Complete the Table | Measurement | # of Sig Figs | Which is the estimated (uncertain) digit? Circle it!!! | |---|---|---| | 0.000234 | 3 | 0.000234 | | 300 | 1 | 300 | | 2003.0 | 5 | 2003.0 | | 1.53 x 10³ | 3 | 1.53 x 10³ | Write the following measurements in scientific notation: 480,000 = 4.8 x 10⁵ 0.24 = 2.4 x 10⁻¹ 8. What is density? Describe how substances with different densities behave (egg demo) D = m/v mass per unit of volume 9. Describe the changes that matter undergoes. PHYSICAL CHANGE: does not change substance's composition CHEMICAL CHANGE: substance changes into a new substance 10. Classify the following as Chemical or Physical changes. | Verbal Description of Change | C or P? | |---|---| | a. Iron is melted. | P | | b. Hydrochloric acid produces carbon dioxide gas when mixed with sodium bicarbonate. | C | | c. Hexane vapors burn to produce CO₂ and H₂O. | C | | d. NaCl dissolves in water to form a saline solution. | P | | e. Liquid water boils at 100°C at sea level. | P | | f. Aluminum foil is cut into smaller pieces. | P | | g. A silver necklace tarnishes. | C | | h. Sand is mixed with pebbles and water. | P | | k. Sand is mixed with pebbles and water. | P | 11. Describe the different categories of matter. ELEMENT: Single substance that can't be separated into simpler substances by physical or chemical means COMPOUND: made of 2 or more elements chemically combined MIXTURE: 2 or more substances combined physically 12. Explain the difference between a homogeneous and a heterogeneous mixture. Give 2 examples of each. HOMOGENEOUS: Same throughout ex: Gatorade, air HETEROGENEOUS: Composition varies ex: Salad, Soup Stoichiometry 71. Explain the 3 steps for solving stoichiometry problems. STEP 1: convert the given quantity to moles STEP 2: use the mole ratio to convert to moles of the unknown STEP 3: convert moles of unknown to grams/liters/particles Use this equation to solve the next 3 Stoichiometry problems. 2H₂S(g) + 3O₂(g) → 2SO₂(g) + 2H₂O(g) 72. How many moles of SO₂ will be produced by the reaction of 4 moles O₂? 4 moles O₂ * (2 moles SO₂ / 3 moles O₂) = 2.7 moles SO₂ 73. If we start with 60g H₂S and excess O₂, how many grams of H₂O will be produced? 60g H₂S * (1 mole H₂S / 34.09g H₂S) * (2 moles H₂O / 2 moles H₂S) * (18.02g H₂O / 1 mole H₂O) = 31.7g H₂O 74. How many liters of oxygen are needed to produce 2.48 liters of SO₂? 2.48 L SO₂ * (1 mole SO₂ / 22.4 L SO₂) * (3 moles O₂ / 2 moles SO₂) * (22.4 L O₂ / 1 mole O₂) = 3.72 L O₂ 75. If 125.0 grams of lead (II) nitrate and 115.0 grams of sodium iodide are used in the reaction below, how many grams of sodium nitrate can be formed? What is the limiting reagent? Pb(NO₃)₂(aq) + 2NaI(aq) → PbI₂(s) + 2NaNO₃(aq) 125.0g Pb(NO₃)₂ * (1 mole Pb(NO₃)₂ / 331.22g Pb(NO₃)₂) * (2 moles NaNO₃ / 1 mole Pb(NO₃)₂) * (85g NaNO₃ / 1 mole NaNO₃) = 62.69g NaNO₃ 115.0g NaI * (1 mole NaI / 149.89g NaI) * (2 moles NaNO₃ / 2 moles NaI) * (85g NaNO₃ / 1 mole NaNO₃) = 64.29g NaNO₃ The limiting reagent is Pb(NO₃)₂ because it produces less NaNO₃.

Chem Semester 1 Guide Key

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