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Concentration

Concentration. http://www.flickr.com/photos/lesliekeating/2074186549/. Todays Lesson. What Is Concentration? Concentration Equation Some fun work Go through test answers Some housekeeping. Last Lesson. So what did we learn last lesson?? Can someone remind me??. Limiting Reactants.

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Concentration

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  1. Concentration http://www.flickr.com/photos/lesliekeating/2074186549/

  2. Todays Lesson • What Is Concentration? • Concentration Equation • Some fun work • Go through test answers • Some housekeeping

  3. Last Lesson • So what did we learn last lesson?? • Can someone remind me??

  4. Limiting Reactants • Yes – we learnt about limiting reactants! • A limiting reactant is the specific reacting chemical (be that element or molecule) which limits how much product can be made. • So to put it simple – when the limiting reactant runs out no product can be made!

  5. Our Big 5 Limiting Reactant Rules! • Balance the equation • Find out the number of moles/mass you have for your reactants. • Find out what your limiting reactant is! • Look at the ratios. Make sure they match up. • Find out how much mass/moles of product you have

  6. Concentration • According to the dictionary (I know your all thinking kill me now!!), concentration is: • thestrengthofasolution,espthe amount of dissolved substance in a given volume of solvent, usuallyexpressed in moles per cubic metre or cubicdecimetre(litre) • http://dictionary.reference.com/browse/concentration

  7. Normal English! • Concentration is how many particles are present in a given volume. • Chemists use a volume called the cubic decimeter – abbreviated as dm3. • The unit of concentration measurement is moles per decimeter cubed or mol.dm3 • Now we have the fun task of completing some example questions  (yay – now my life is complete!!)

  8. Example 1 • I have 2L of HCl at 1 mol.dm3 , what mass of HCl would I have • It’s easier than it looks. • First, find out the number of moles of HCl • Second, find out the Mr of HCl • Third, find out the mass by moles X Mr • Workings out on next slide:

  9. Example 1 Continued • I have 2L of HCl at 1 mol.dm3 , what mass of HCl would I have • 2L X 1 mol = 2 mol • Mr of HCl is 1 + 35.5 = 36.5 • Mass is 2 X 36.5 = 73g of HCl • It’s all done!

  10. Example 2 • What mass of KCl would I need to make a 0.2 mol/dm3 solution ? • So how do we work it out? • Work out the Mr of KCl • Work out the mol and volume (we already have this • To find out mass, mol X Mr

  11. Example 2 Continued • What mass of KCl would I need to make a 0.2 mol/dm3 solution ? • Mr of KCl is 39 + 35.5 = 74.5 g • Work out mol/dm3 ? It’s 0.2 mol/dm3 • Find mass. 0.2 X 74.5 = 14.9 g of KCl

  12. Calculating Unknown Concentrations! • Here is a new formula! We will be using it a big for acid/bases. • C1V1 = C2V2 • C1 = Concentration 1 • V1 = Volume 1 • C2 = Concentration 2 • V2 = Volume 2

  13. An Example • I have 25 cm3 of HF (an acid) at 0.8 mol / dm3. What mol / dm3 would I need for 50 mL of NaOH (a base)? • This is easier than it looks. Here is how we work it out! • Work out which is C1, C2, V1, and V2. • Manipulate the C1V1 = C2V2 equation.

  14. Explanation • I have 25 cm3 of HF (an acid) at 0.8 mol / dm3 . What mol / dm3 would I need for 50 cm3 of NaOH (a base)? • C1 = 0.8 mol / dm3, C2 = ???, V1 = 25 cm3 , V2 = 50 cm3 • Equation C2 = C1V1 / V2 • C2 = 0.8 X 0.025 dm3 / 0.05 dm3 • Equals 0.5 mol / dm3

  15. Small Worksheet • We will have around 20 mins to do this! • Then we will go through our test answers!!

  16. Housekeeping • Next lesson – we will be learning titrations for acid/bases. It will help us learn the C1V1 = C2V2 equation along with helping to explain acid base reactions. • Please give all tests back – they cannot go home yet!!

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