DENSITY OF A SOLUTION ppt

DENSITY OF A SOLUTION

CHEM 1103 - GEN CHEM I LAB

JOKE OF THE WEEK

  • Question: Why do chemists never encounter problems?

  • Answer: Because they have all the solutions.

PURPOSE

  1. Learn to make volume and mass measurements.

  2. Make solutions.

  3. Determine density graphically and mathematically.

PART A: CALIBRATION CURVE

  • Objective: Calculate the solid needed to make 100.0 mLs of different percentages of sugar/salt solutions.

  • Tasks:

    • Determine solid needed to make:

    • 100.0 mLs of a 5.0% sugar/salt solution.

    • 100.0 mLs of a 15.0% sugar/salt solution.

    • Dilution Calculations:

    • Determine volume needed to make:

      • 100.0 mLs of a 10.0% sugar/salt solution.

      • 100.0 mLs of a 20.0% sugar/salt solution.

    • Stock solution = 30.0%

    • Note: 5% and 15% solutions have been premade.

PROCEDURE: MAKE KNOWNS

  • Mass Percent Calculation:

    • To find the mass of solute (sugar) in a solution, use the equation:
      ? ext{% mass}= rac{ ext{mass of solute (g)}}{ ext{mass of solution (g)}} imes 100

  • The rearranged equation to solve for the mass of solute is:
    ext{mass of solute (g)} = ? ext{%} rac{ ext{mass of solution (g)}}{100}

HOW TO MAKE A 5.0% SUGAR/SALT SOLUTION FROM SOLID

  1. Equation Setup:

    • 5.0 ext{% mass} = rac{X ext{ g sugar}}{X ext{ g sugar} + 100.0 ext{ g H2O}}

  2. Rearranging and Calculating:

    • Divided, multiplied both sides, and combined like terms:

    • Final calculation: X = 5.3 ext{ g sugar}

HOW TO MAKE A 15.0% SUGAR/SALT SOLUTION FROM SOLID

  1. Equation Setup:

    • 15.0 ext{% mass} = rac{X ext{ g sugar}}{X ext{ g sugar} + 100.0 ext{ g H2O}}

  2. Rearranging and Calculating:

    • Final calculation: X = 17.6 ext{ g sugar}

DILUTION EQUATION

  • The dilution equation is given as:
    C₁V₁ = C₂V₂

  • Where:

    • C₁ = Initial concentration

    • V₁ = Volume of stock solution

    • C₂ = Final concentration

    • V₂ = Final volume

  • Rearranged to solve for the volume needed:
    V₁ = rac{C₂V₂}{C₁}

HOW TO MAKE A 10.0% SUGAR/SALT SOLUTION BY DILUTION

  1. Use the dilution equation for different concentrations.

  2. Example calculation for a 10.0% solution using a 30.0% stock solution:

    • V₁ = rac{10.0 ext{%} imes 100.0 ext{ mLs}}{30.0 ext{%}} = 33.3 ext{ mLs}

PART A: MAKE SOLUTIONS

For Today’s Lab

  • Use a volumetric flask filled with deionized water (DI H₂O) as the solvent.

  • Steps:

    1. Measure the required aliquot of the stock solution and put in the flask.

    2. Fill the flask to the line on the neck (bottom of the meniscus).

    3. Stopper and shake to mix.

  • Beakers:

    • Put solutions made into individual labeled beakers.

    • Do not pipet directly out of the flask.

    • Use a 250 mL beaker for stock solution; fill ~1/2 full (share with partner).

PART B & C: % MASS DETERMINATIONS

  1. Pipet 10 mLs of each known solution (0%, 5%, 10%, 15%, 20%), DI H₂O, and an unknown into a weighed beaker.

  2. Weigh the beaker plus the solution.

  3. Perform trials in triplicate:

    • Steps include weighing, then discarding the solution to waste after weighing.

  4. Note: Use a 100 mL beaker to get DI H₂O, 5%, 15%, and unknown solutions and fill ~1/2 full.

RESULTS

  • Calculation Steps:

    1. Subtract beaker weight from each mass recorded.

    2. Sum the masses up.

    3. Divide by 60 mLs to get the average mass of the solution.

      • Note: Total of trials is 10 mLs + 20 mLs + 30 mLs = 60 mLs.

  • Calibration Curve:

    • Determine density of known solutions using average mass.

    • Graph density against % mass of known concentrations.

  • For Unknowns:

    • Determine density of unknown solution and calculate using the graph to find % mass of the unknown.

  • Relationship Observations:

    • Discuss trends seen in graph: explore direct versus inverse proportional relationships.

WASTE SHEET

  • Learning from the lab, students must maintain a record of product accumulation:

    • Institution: University of Dallas, Chemistry Department

    • Details to Document:

    • Code, Date added (mm/dd/yy), Description (Unk and known sugar solutions), Amount of each (g or mL), Initials.

FOR NEXT TIME…

  • Upcoming Tasks:

    1. Lab write-up and post-lab questions are due in 48 hours in the notebook depository.

    2. Print and read: Separation Exploration.

    3. Complete pre-lab quiz on Brightspace before attending lab.