QUESTIONS AND ANSWERS

QUESTIONS AND ANSWERS

Answers CHEM 120 Exam 2 (Latest - and Answers 100% Correct

TESTED AND CONFIRMED A+ ANSWERS

1.) CONVERSIONS IN METRIC UNITS

How many kilograms are in 143 grams?Using KHDBDCM Starting with Grams (g) – base unit. Moving to kilograms (kg); move the decimal three spaces to the right 143 g – 0.143 g

Using conversion factors KNOW that kilo = 1000 base 143 g x (1 kg/1000g ) = 0.143 kg

2.) CONVERSIONS WITH ENGLISH UNITS

How many milliliters are in 13.5 oz?MUST USE CONVERSION FACTORS (oz, lb, feet, inches…) Always start with what you know…. Figure out where to go 13.5 oz ? mL 13.5 oz 1 cup 1 pt 1 qt 1 L 1000 mL

• oz 2 cups 2 pt 1.06 qt 1 L

= 398 mL are in 13.5 oz

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Question: is ATM (atmospheres) a standard number?

Answer; No, it’s a unit. There’s not a particular number there. The gas constant has a number and a unit because it is a constant; atmospheres will differ depending on the problem

Stoichiometry: Practice questions.

22.0 g of propane will combine with what mass (g) of O2?

C3H8 + 5O2 3CO2 + 4H2O

c- 3 c -3

H – 8 H-8

O- 10 O – 6 + 4 = 10

GIVEN: want: 22.0 g of C3H8 ? g O2 Balanced chem equation

C3H8 + 5O2 3CO2 + 4H2O

Periodic table (moles to grams or grams to moles ONE COMPOUND)

1.) Check to make sure the equation is balanced – DONE 2.) Start with the known 3.) … were you given moles? If not, find moles using the periodic table to take grams to moles of one compound.

4.) From moles, use the balanced chemical equation. BCE compares moles to moles of different compounds 5.) If you were looking for moles, stop. If you need grams, use the periodic table to convert moles – grams of the same compound.

22.0 g C3H8 1 mol C3H8 5 mol O2 32.0 g O2 44.1 g C3H8 1 mol C3H8 1 mol O2

= 79.8 g O2

Calculate the molar (molecular) mass of C3H8 = units are g/mol NOT grams Mass – units are grams ANY MASS from the Periodic Table has units of grams per mole (g/mol)

• x 12.011 g/mol + 8 x 1.008 g/mol = 44.097 g/mol
• mole C3H8 = 44.097 g

CALCULATE THE MOLAR (MOLECULAR) MASS OF O2. 31.998 G/MOL

• mol O2 = 31.998 g

OXIDATION/REDUCTION

Pg. 218, figure 8.2

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Comparing the reactants and the products

OXIDATION REDUCTION

Gain Oxygen Lost oxygen Lose Hydrogen Gains Hydrogen Lose electrons Gains electrons Increases oxidation number Decreases oxidation number

NaBr + Cl2 NaCl + Br2

+1 -1 0 +1 -1 0

Bromine oxidation number INCREASED Chlorine oxidation number DECREASE

-5 -4 -3 -2 -1 0 1 2 3 4 5

What is oxidized: NaBr REDUCING AGENT

What is reduced: Cl2 OXIDIZING AGENT

Oxidizing agents (cause oxidation; get reduced) Reducing agent (cause reduction; get oxidized)

• The Scientific Method

• Hypothesis : a testable educated guess

• Experiments: how we test hypotheses

o Variable: idea to be tested (only one)

o Control: something the variable is tested against; what your testing

against

o Experimental protocol: how do you do the test?

o Results: data generated comparing variable to controls. Includes statistics

to show results are meaningful