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Solutions and Stoichiometry

Solutions and Stoichiometry. A solution is made up of a Solute and a SolventA Solute is what is being dissolved.A Solvent is what does the dissolving (the most stuff" present)Note: not all solutions are Liquids Air (O2 in N2)Alloys (metals mixed with other metals) SteelBrass (copper and

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Solutions and Stoichiometry

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    1. Solutions and Stoichiometry Many times the reactants and/or products of chemical reactions are water solutions. In these cases the concentration of the solution must be determined in order to determine amounts of reactants or products The concentration of a solution is a measure of the amount of solute that is dissolved in a given amount of solvent

    2. Solutions and Stoichiometry A solution is made up of a Solute and a Solvent A Solute is what is being dissolved. A Solvent is what does the dissolving (the most “stuff” present) Note: not all solutions are Liquids Air (O2 in N2) Alloys (metals mixed with other metals) Steel Brass (copper and zinc) Bronze (copper and tin)

    3. Concentration For individual elements, compounds and molecules (solid & liquids): Density (g/mL) For solutions: Molarity (M) (moles/liter) (“Molar”) Molality (m) (moles/kilograms) (“Molal”) (rarely used)

    4. Molarity The most common concentration unit is Molarity

    5. Molarity Calculations How many grams of NaOH are required to prepare 250 cm3 of 0.500 M solution? Molar Mass of NaOH = 23+16+1 = 40.0 g/mol 250 cm3 = 0.250 dm3

    6. Molarity Calculations Calculate the concentration of a NaCl solution that contains 24.5 g of NaCl in 250 cm3 of solution. Molar mass of NaCl = 23.0 + 35.5 = 58.5

    7. Stoichiometry Calculations Involving Solutions 1 Copper metal reacts with nitric acid according to the following reaction: 8 HNO3 (aq) + 3 Cu ? 3 Cu(NO3)2 (aq) + 4 H2O (l) + 2 NO (g) What volume of 8.00 M HNO3 would be required to consume a copper penny whose mass is 3.08 grams?

    8. Stoichiometry Calculations Involving Solutions 2 15.0 cm3 of a 0.500 M AgNO3 solution is required to precipitate the sodium chloride in 10 cm3 of a salt solution. What is the concentration of the solution? AgNO3 (aq) + NaCl (aq) ?AgCl (s) +KNO3 (aq) Molar Mass NaCl = 23.0 + 35.5 = 58.5 g/mol

    9. Dilutions Sometimes, solutions of lesser concentration need to be made. This is done by adding solvent. Using the equation, M1 V1 = M2 V2 we can calculate a volume or molarity of solutions. M1 is the Molarity of the starting solution V1 is the Volume of the starting solution M2 is the Molarity of the end solution V2 is the Volume of the end solution Knowing any 3 variables, we can calculate the last variable (algebra).

    10. Dilutions Using the equation, M1 V1 = M2 V2 What is the final molarity of NaOH solution if 10 cm3 of 3.5 M NaOH solution is diluted to 250 cm3? M1 = 3.5 M V1 = 10 cm3 M2 = ? V2 = 250 cm3 M1 V1 = M2 V2 3.5M x 10 cm3 = M2 x 250 cm3 M2 = 3.5M x 10 cm3 250 cm3 M2 = 0.14 M NaOH

    11. Dilutions Using the equation, M1 V1 = M2 V2 How much water must be added to change 150 cm3 of 2.5 M HNO3 to a 0.75M solution? M1 = 2.5 M V1 = 150 cm3 M2 = 0.75 M V2 = ? cm3 M1 V1 = M2 V2 2.5 M x 150 cm3 = 0.75 M x V2 V2 = 2.5M x 150 cm3 0.75 M V2 = 500 cm3 BUT remember, that’s the TOTAL volume. 500 cm3 – 150 cm3 = 350 cm3 water added.

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