Chem 220 - Exam I – Spring 2014

Name

Date

SHOW ALL WORK!!!!!!

Record all answers with the correct number of significant digits

GOOD LUCK 

Points Earned

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Total Points

1. (8 pts)Find the solution with the correct number of significant digits:

a. 5.0 + 0.01 + 20.0 =

b. (6.2 x 10-5)/ (62 x 10-5) =

c. 6.2 - 3.54 + 21.0 =

2. (6 pts) Give the number of significant digits in the following:

a. 53,000

b. 0.00250

c. 500.0

3. (3 pts)Give the accurate reading of this thermometer

4. (5pts)Prove that 20 ppm is equal to 20 µg/mL in an aqueous solution

5. (5 pts) Concentrated hydrofluoric acid contains 49.0 wt% hydrofluoric acid and has a density of 1.30 g/mL. What is theconcentration of this solution in units of ppb?

6. (15 pts)How many mL of a 45.0 N H3PO4 solution (density of 1.69g/mL) do you need to make 20.0 mL of a 5.0 x 105 ppm H3PO4 solution? SHOW ALL WORK for FULL CREDIT

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7. (20 pts)When you mix 500. µg of Na(s) with 20.0mL of a 4.00ppm solution of Ca3(PO4)2(aq), what is the molarity of the Ca2SO4(aq) solution that you form according to the reaction below.SHOW ALL WORK for FULL CREDIT

Na(s) + Ca2+(aq) ------> Na+(aq) + Ca+(aq)

8. (18pts) How much mass in grams of NaCl will you produce from mixing 10.0 mL of 37.2 pph HCl solution (density 1.19 g/mL) with a NaOH solution that has a molality of 25.45 and a solvent volume of 0.0495 L.

SHOW ALL WORK for FULL CREDIT

9. (20 pts TOTAL) You were at a Super Bowl party and your friend said that the “water” that he was about to drinksmelled like vinegar. You remember from your Analytical Chemistry class that vinegar contains 5.00wt% acetic acid (CH3COOH); density of this dilute acetic acid is 1.00 g/mL. Fortunately, Steve (your lab manager) is at the party and he mentions that you can titrate the “water” to determine if and how much acetic acid is in the water.

You take a 100.0mL sample of water from the pitcher that your friend got it out of and decide to only use 20.0mL. However, since the water smells a lot like vinegar, you then decide that you will dilute the 20.0mL with 100.0mL of water and then use 20.0mL of the diluted sample to do your titration. You eventually determine that the concentration of acetic acid in your diluted sample is 0.146 M.

  1. (15 pts) What is the concentration of acetic acid in the “water” that your friend was about to drink? SHOW ALL WORK for FULL CREDIT
  1. (5 pts) What quantitative proof can you give your friend to confirm that what he was going to drink was in fact vinegar? SHOW ALL WORK for FULL CREDIT