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Limiting Reactants

Limiting Reactants. Today’s Lesson. Some housekeeping Explaining Limiting Reactants Finishing Off Casein Experiment. Housekeeping. So, has my test been marked?

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Limiting Reactants

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  1. Limiting Reactants

  2. Today’s Lesson • Some housekeeping • Explaining Limiting Reactants • Finishing Off Casein Experiment

  3. Housekeeping • So, has my test been marked? • Answer – yes. However, one student has not completed test and the teachers need to cross-mark level 5/6 questions. You might get your test marks back tomorrow. • When do we swap classes? • Wednesday – you will have MrLorimer then! • Your still stuck with me for another 12 weeks.

  4. Some Reminding • In a Chemical Reaction, it often works like this: • A + B  C + D • A + B are the reactants • C + D are the products • Balance the reactants and products. Make sure there is the same amount of atoms and charge on each side! http://www.digitalphotographybasics.com/wp-content/uploads/product-photography.jpg

  5. How Do I Work Out Moles Again? • If I have 6 grams of Carbon, how many moles of Carbon do I have? • Remember the rule: mass/Ar (if single atom) • or mass/Mr (if molecule or compound • So, it goes a little something like this: • Ar of C = 12g, Mass of C = 6g • 6/12 = 0.5 mol

  6. A Slightly Harder Example • I have 8 grams of O2. Remember there is 2 Oxygen molecules! • So our rule is mass/Mr • So it goes a little something like this: • Mass = 8 grams, Mr = 32g (2 X 16) • 8/32 = 0.25 moles of O2

  7. Small Trick For Chemical Reactions • Here is a small trick that can come in handy. Remember that it’s just a trick, and does not always work. • AB + CD  AD + BC • Eg; NaOH + HCl  NaCl + H2O • A = Na. B = OH, C = H, D=Cl • The cation (or positive charged ion) always goes first

  8. Limiting Reactants • In a chemical reaction, when there is not enough of one reactant, then only a certain amount of product can form. • Below is one example. • I have 16 grams of Oxygen gas (O2) and an unlimited amount of Hydrogen gas (H2). How many moles of water can I make? • 2H2 + O2 2H2O

  9. Continued • Our Rules • Balance the equation (already done) • 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

  10. Continued • I have 16 grams of Oxygen gas (O2) and an unlimited amount of Hydrogen gas (H2). How many moles of water can I make? • 2H2 + O2 2H2O • Moles of Oxygen Gas is mass/Mr (Mass = 16) (Mr = 32) • 16/32 = 0.5 moles of Oxygen gas • Our Ratio for Hydrogen to Oxygen is 2:1, so we will have 1 mole of Hydrogen gas (H2). • Hydrogen Gas to Water is 1:1 – so we have 1 mole (or 18 grams of water – remember molar mass is moles * Mr or Ar depending on if it is an atom or molecule)

  11. Ultra Fun Worksheet • I’ll now do some more examples on the board for notes – fun fun!! • We will also complete the worksheet handed out.

  12. Experiment • Let’s burn out Casein. • Homework – Balancing Chemical Equations Worksheet (due next week) • Next lesson – concentration calculations!! 

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