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**Solve Chemistry Math Problems**

“When in doubt, go to moles.”

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**Use Dimensional Analysis**

Analyze the labels Change them with converting fractions Do the “number math” last (after all the labels cross off so they are the same on both sides of your equation.)

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**1: Identify your goal unit:**

What label goes with the number you want to find? Is it grams, moles, liters, joules, or some other unit? Is it a combined unit, like moles/liter, or cal/(gram*Celsius)?

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2. Write the label Write an = sign, and leave a space for the answer number on the far right side of your paper. Then write the label you want with your answer.

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**3. Choose a number to convert**

Choose one of the numbers you’re given, based on its similarity to the goal unit. On the far left side of your paper, write that number as a two line, flat fraction.

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**4. Convert units multiply by two line, flat fractions**

Cross out any unit label you find on both the top line and the bottom line. Continue adding converting fractions and crossing out labels. The top must equal the bottom. Memorize the common converting fractions. When all the labels left before the equals sign match the labels after the equals sign, you’re almost finished.

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6. Multiply then divide Multiply all the numbers across the top line of your two line fractions. Then divide that answer by each of the numbers across the bottom. Write the result before the goal label on the right.

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**Common converting fractions**

Atomic mass, formula mass: X grams = 1 mole STP liters of any gas: 22.4 Liters = 1 mole Avogadro’s Number: 6.02X1023 particles = 1 mole

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**Gas Equations Dalton’s Law of Partial Pressures:**

P1 + P2 + P3 … = Ptotal Combined Gas Law: P1V1T2 = P2V2T1 (T must be Kelvin) Ideal Gas Law: PV = nRT

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Solutions Molarity = M M = moles of solute / Liter of solution

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**Heat and Energy Specific Heat : changing temperature # calories/gramoC**

Heat of fusion: melting or freezing #Joules/mole Heat of vaporization: boiling or condensing # Joules/mole

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**Units Moles Grams Liters Energy: calories or Joules**

Temperature: Kelvin, Celsius, Fahrenheit Pressure: Atmospheres, Torr, mm Hg, KiloPascals Particles (atoms, ions, electrons, molecules, formula units…)

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**Prefixes Use these as converting fractions, too. Mega = M = 106**

Kilo = K = 103 centi = c = 10-2 milli = m = 10-3 micro = “mu” (Greek letter) = 10-6

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**Liters of A Liters of B Grams of A Moles of A Moles of B Grams of B**

X Ratio Liters of B X Ratio X 22.4 1/ 22.4 X 22.4 1/ 22.4 Grams of A Moles of A Moles of B Mole/Grams Grams of B X Ratio Grams/Mole X Ratio Grams/Mole Mole/Grams 1/6.02 1023 X6.02 1023 1/6.02 1023 X6.02 1023 Particles of A X Ratio Particles of B X Ratio Mole Map

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Learn the system Dimensional analysis is a procedure you can use to solve most problems. It’s not just for chemistry. You will be given many equations on the SOL test. You still need to memorize some equations.

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Good Luck!

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Unit 12 Mass and Moles.

Unit 12 Mass and Moles.

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