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Concentration

Concentration. Concentrated versus Dilute. solvent. solute. Lower concentration Not as many solute (what’s being dissolved) particles. Higher concentration More solute (what’s being dissolved) particles. Concentration.

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Concentration

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  1. Concentration

  2. Concentrated versus Dilute solvent solute Lower concentration Not as many solute (what’s being dissolved) particles Higher concentration More solute (what’s being dissolved) particles

  3. Concentration • Concentration – a ratio of the amount of solute dissolved over the total amount of solution. • There are several ways to show concentration – we will only focus on one

  4. Quick Mole Review • 1 mole = 6.02 × 1023 molecules • The molar mass of a molecule is found by adding up all the atomic masses in the atom ( from the periodic table) • Molecular mass in grams = 1 mole of that molecule

  5. Quick Mole Example Example: How many moles are in 25.5 g NaCl?

  6. Na 1  22.99 g/mole 22.99 g/mole =  + 35.45 g/mole Cl 1 35.45 g/mole = 58.44 g/mole Quick Mole Example Example: How many moles are in 25.5 g NaCl? 1 mole NaCl molecules = 58.44 g 25.5 g NaCl mole NaCl 1 = _______ mole NaCl 0.436 58.44 g NaCl

  7. Molarity • Molarity (M) is a concentration unit that uses moles of the solute over the total volume of the solution

  8. Molarity Example Example: If you dissolve 12 g of NaCl to make 150 mL of solution, what is the molarity?

  9. Na 1  22.99 g/mole 22.99 g/mole =  + 35.45 g/mole Cl 1 35.45 g/mole = 58.44 g/mole Molarity Example Example: If you dissolve 12 g of NaCl in 150 mL of solution, what is the molarity? 1 mole NaCl molecules = 58.44 g 12 g NaCl mole NaCl 1 = _______ mole NaCl 0.21 58.44 g NaCl Remember to change mL to L! 150 mL of water = 0.150 L 1.4 M NaCl

  10. Dissolving substances • Substances are dissolved by a process called HYDRATION or SOLVATION • The solvent attracts to the solute • New intermolecular forces are formed • The solvent “carries off” the solute particles and surrounds the ions – keeping them dissolved!

  11. - - O H H + Dissolving Ionic Compounds - + Ionic compound water Water molecules are polar and they attract to the charges of the ions in an ionic compound. + - If the ion attraction is weak enough, the water can successfully pull them apart. + - + - + -

  12. - - + O + H H + Dissolving Ionic Compounds - + Ionic compound water As more ions are “exposed” to the solvent, they can be carried off as well. - - + - + -

  13. - O H H + Dissolving Ionic Compounds - + Ionic compound water + - These free-floating ions in the solution allow electricity to be conducted - + - + - + -

  14. Electrolytes • Electrolytes – substances that produce free floating ions and can conduct a current when dissolved. • Ex. NaCl(s) Na+1(aq) + Cl-1(aq) • BaI2  • Ca3(PO4)2  • K2O 

  15. + - + Solute, sugar (polar) Solvent, water (polar) - - + - + - + - + - + Dissolving Covalent Compounds Water forms intermolecular forces with the polar ends of the solute and “carries” the solute particles away.

  16. + - + Solute, sugar (polar) Solvent, water (polar) - - + - + - + - + - + Dissolving Covalent Compounds NOTICE how the polar covalent molecules themselves do not split into charged ions—the solute molecule stays together and just separates from other solute molecules.

  17. Non-electrolytes • NON-ELECTROLYTES - Molecules that separate from other molecules but DO NOT create free-floating ions 1 C6H12O6(s)  1 C6H12O6(aq)

  18. Breaking up Electrolytes • Leave polyatomic ions in-tact (including the subscript within the polyatomic ion) • All subscripts not on a polyatomic ion become coefficients • Be sure to include charges on the dissociated ions! Example: Break up the following ionic compounds into their ions KNO3 Ca(NO3)2 Na2CO3

  19. Breaking up Electrolytes • Leave polyatomic ions in-tact (including the subscript within the polyatomic ion) • All subscripts not within a polyatomic ion become coefficients • Be sure to include charges on the dissociated ions! Example: Break up the following ionic compounds into their ions  K+1 + NO3-1  Ca+2 + 2 NO3-1  2 Na+1 + CO3-2 KNO3 Ca(NO3)2 Na2CO3

  20. Let’s Practice #3 Example: What are the molarities of the ions made in a 0.75 M solution of Ca(NO3)2

  21. Let’s Practice #3 Example: What are the molarities of the ions made in a 0.75 M solution of Ca(NO3)2 Ca(NO3)2 Ca+2 + 2 NO3-1 For every 1 Ca(NO3)2, there will be 1 Ca+2 and 2 NO3-1 ions Ca+2 = 0.75 M NO3-1 = 1.5 M

  22. Types of Electrolytes Non-Electrolytes Strong Electrolytes Weak Electrolytes Covalent Compounds Ionic compounds Strong Acids Strong Bases Ionic Compounds Weak Acids Weak Bases No molecules separate—ions are not formed Fully Ionize in solution Only a few ions are created in water DOESN’T CONDUCT STRONGLY CONDUCTS CONDUCTS WEAKLY

  23. Misconceptions about dissolving • Dissolved Solids DO NOT dissappear • In the solid it is a LARGE enough particle collection to see! • After dissolving, the particles are ALONE and too small to see

  24. Another Way to Think about Solutions: Super-Saturated Unsaturated Saturated Holds more solute than what should be dissolved at that temperature More solute can be dissolved at that temperature No more solute can be dissolved—it’s “full” at that temperature In general, more solid will dissolve at higher temperatures!

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