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Limiting Reactants

Limiting Reactants. Today’s Lesson. Explain Concentration Complete Worksheet  Introduce Acids & Alkalis Textbook Questions – I bet you’ve missed those!!. Concentration. According to the dictionary (I know your all thinking kill me now!!), concentration is:

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Limiting Reactants

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  1. Limiting Reactants

  2. Today’s Lesson • Explain Concentration • Complete Worksheet  • Introduce Acids & Alkalis • Textbook Questions – I bet you’ve missed those!!

  3. 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

  4. 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!!)

  5. 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:

  6. 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!

  7. 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

  8. 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

  9. 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

  10. 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.

  11. 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

  12. Ultra Fun Worksheet • Complete the ultra fun worksheet • If you finish early, get started on this: • Acids & Alkalis Page 44-45 (Questions 1-6)

  13. Don’t Be Too Acidic • One important type of chemicals are called acids. • Examples include: Sulfuric Acid (H2SO4), Vinegar (CH3COOH), Hydrochloric Acid (HCl) and Nitric Acid (HNO3) • Acids are solutions of pure compounds in water • They are corrosive, especially if they have a high molar value • Some acids are strong for the same molar value (eg Sulfuric Acid), but some are weaker (Vinegar or Ethanoic Acid)

  14. Acids #2 • Acids can be tested in different ways. The 2 main ways we will learn are: • Litmus Solution. This solution is purple and will turn red if an acid • Litmus Paper. The paper is blue and will turn red if an acid. • Acids are reactive as they often have a Hydrogen atom that can be removed easily.

  15. Interesting But Don’t Need To Know • When an acidic compound loses an Hydrogen atom, they dissociate an Hydrogen atom. • Some acids like Phosphoric Acid can lose up to 3 hydrogen atoms (H3PO4).

  16. AlkaAlkaAlkali • Another important type of chemical is called alkalis. • They need to be handled carefully as they often can burn the skin if strong. • Examples of Alkali solutions include: Sodium Hydroxide (NaOH), Potassium Hydroxide (KOH) and Ammonia Solution (NH3) • Alkali’s turn red litmus solution blue, and red litmus paper blue

  17. Neutral Substances • Some substances are not classed as acids or bases, as they do not affect litmus paper. • Examples include Salt (NaCl) and Sugar solutions.

  18. pH Scale • The pH scale measures how many hydrogen (H+) atoms are present in water. • If it is acidic, there are more H+ atoms. These are also described as H3O+ or hydronium ions. • If it is basic, there are more OH- compounds. This is often called Hydroxide.

  19. Continued • An acidic solution has a pH less than 7 • An neutral solution has a pH of 7 • An alkaline (or basic) solution has a pH higher than 7

  20. Questions • To be completed at end of class or for homework. • Read Page 44/45 and answer Q 1-6 • Next lesson – titrations of CC Lemon!!

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