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Chemistry Problem-Solving Techniques for Conversions

Learn how to solve chemistry problems with algebraic and conversion methods, focusing on Metric System conversions. Practice using ratio and factor-label methods to convert units accurately. Utilize easy conversion facts for complex problem-solving.

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Chemistry Problem-Solving Techniques for Conversions

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  1. Problem-Solving in Chemistry

  2. Problems in Chemistry • Tend to fall into two categories, algebraic or conversion. • In algebraic problems you are solving for an unknown. • In conversion problems you are changing units.

  3. Conversions within the Metric System Remember, it’s a decimal-based system. Conversions should be easy.

  4. Use the factors in Table C to figure out the conversion fact.

  5. Convert 129 milligrams to grams. Look for milligrams in Table C Find the row: Factor is 10-3 What does that mean? It means 1 X 10-3 g = 1 mg This is the conversion fact!

  6. Conversion Fact or Definition • Once you have your conversion fact, you can choose the ratio method or the factor label method to do the work. 1 X 10-3 g = 1 mg or .001 g = 1 mg Equivalently, 1 g = 1000 mg

  7. Ratio Method as means = 129 mg as 1 mg X g .001g (129 mg) • .001 g = 1 mg • X g X = .129 g 1 X 10-3 g = 1 mg or .001 g = 1mg

  8. Ratio Method 129 mg as 1000 mg X g 1g (129 mg) • 1 g = 1000 mg • X g X = .129 g .001 g = 1mg or 1 g = 1000 mg

  9. Factor-Label Method • In the factor label method, you always take the given and multiply it by the conversion factor. • The conversion factor is a ratio like 12 inches or 1 meter 1 foot 100 cm

  10. Factor-Label Method 129 mg .001 g = .129 g 1 mg Conversion factor Given 1 X 10-3 g = 1 mg or .001 g = 1mg

  11. Factor-Label Method 129 mg 1 g = .129 g 1000 mg Conversion factor Given Use 1 g = 1000 mg

  12. 129 milligrams = 0.129 grams Think about your answer for a moment. Does it make sense? Reality Check Yes, you switched to a larger unit, so the number should be smaller!

  13. Convert 2.765 km to meters. Kilometers to meters From Table C: the factor is 103 Or 1 X 103 meters = 1 km, 1000 m = 1km 2.765 km 1 X 103 meters = 2765 m 1 km

  14. Convert 2.765 km to meters. 2.765 km = 2765 meters Does this answer make sense?

  15. Try a few more problems! • How many liters are in 345 milliliters? • This problem is worded a little differently. Think about how you are doing the conversion. • From ________ to _________?

  16. 345 milliliters to liters 10-3 What’s the conversion fact? 1 X 10-3 liters = 1 milliliter 345 ml 1 X 10-3 l = 0.345 l 1 ml 345 milliliters = 0.345 liters Does this answer make sense?

  17. 8.93 meters 45000 grams 5.9 deciliters 0.078 meter 240000 milligrams

  18. The Factor-Label Method orDimensional Analysis • A more general conversion technique. • More powerful in multistep problems. • Much loved by chemists!

  19. Problem: Convert 3.5 years to seconds. What information do you need to solve this problem? You need to know a bunch of relationships or equalities. We use these equalities to make conversions factors.

  20. For days to seconds, the relationships are? • 1 year = 365 days • 1 day = 24 hours • 1 hour = 60 minutes • 1 min = 60 seconds Use the equalities to set up conversion factors. Conversion factors are ratios.

  21. Convert 3.5 years to seconds • In the factor-label method, you always multiply! • Let the units do the work in setting up your conversion factors.

  22. 3.5 years X 365 days X 24 hours X 60 min X 60 sec 1 year 1 day 1 hour 1 min And the answer is … 110,376,000 seconds

  23. Problem: How many quarters in $23.00 • Recall: What relationship do you need to solve this problem? • Set-up: How would you set the problem up?

  24. $23.00 X 4 quarters = the # of quarters 1 dollar $23.00  92 quarters

  25. You just have to be a little careful when you are working with less familiar units. Take your time! Try converting 192 cm to meters.

  26. Recall: 1 m = 100 cm Set-up: 192 cm X 1 meter = 1.92 meter 100 cm

  27. Use the factor-label method for these! 14 quarts 3700 milliliters 2.7 meters 0.0565 grams 23.468 kilometers

  28. K H D  d c m • “Kids have dropped over dead converting metrics.” •  = gram, meter, sec, liter, etc. • Upper-case: kilo or 1000X, hecto or 100X, deka or 10X • Lower-case: deci or 1/10, centi or 1/100, milli or 1/1000. • As the unit gets smaller, the number has to get bigger. • Convert 25 mg to grams. Move decimal 3 places to the left, or .025 grams.

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