Determination of the Amount of Copper in Brass Colorimeter Labs What is the Relationship Between the Amount of Transmitted Light Through a Solution and Its Concentration? Determination of the Amount of Copper in Brass

Thursday’s Lab The important thing to take away from Thursday’s lab-that you need to use on Friday-is how to setup a dilution series for a standard solution, and use the colorimeter to make a calibration curve. Prelab questions need to be answered on plain paper. Postlab questions will go in your notebooks. If you have questions here, we can discuss it next week.

Make changes to data table

You will need to print your interpolated graph. (See next slide You will need to print your interpolated graph. (See next slide.) Copy your absorbance values into your notebook. If we have trouble printing, you can enter your data into LoggerPro Light or Excel later.

Results From the analysis tab, do a curve fit-linear. From the analysis tab, interpolate your absorption value for the brass solution. While on that screen, try to autofit your graph into the available window. Print the screen from the file menu.

Using a pipet and pipet filler: Watch video below https://www.youtube.com/watch?v=d7Dc3iWKo70

Setting up the LabQuest http://www.vernier.com/training/videos/play/?video=197

Friday’s Lab Determination of Percent Copper in Brass

Prelab Questions Part I: Do on a separate sheet of paper. Turn in with lab. Part II: #1: Here is the equation (You’re welcome!) Cu(s) + 4HNO3 (aq) Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l) Answer #2 & #3 in your lab notebooks before your procedure for Part II. For #4, use the graphed data from the Prelab questions in Part I to find the [Cu].

Procedure-Part I See next slide When writing your procedures, make the following changes. As written in handout: See next slide

Procedure-Part I Page 2, direction #2 tells you to make the standard Cu(NO3)2 solution. I will have this already made up for you. The solution will be 0.400M.

Data Table Design your data table as follows: Have the calculations done before lab. Continue with written procedure with step 4. Standard Stock Soln. (mL) H2 O (mL) Molarity (µM) Absorbance 1 10.00 0.00 0.400 2 8.00 2.00 0.320 3 6.00 4.00 4 5 6

Procedure-Part II Replace the above instruction with what follows on the next slide. You can shorten this in your write-up.

Procedure-Part II Obtain a piece of brass and a weighing dish. Cut the brass into 5-6 pieces. (This will shorten the time necessary for the reaction.) Get another weighing dish and zero the balance with the empty dish on the platform. Add the brass to the dish and find the mass of the brass to nearest 0.001g. Add the brass to a 25.0 mL volumetric flask.

Reaction with Nitric Acid Calculate the volume of concentrated nitric acid needed for your sample. ___𝑔 𝐶𝑢× 1𝑚𝑜𝑙 𝐶𝑢 63.55𝑔 𝐶𝑢 × 4 𝑚𝑜𝑙 𝐻𝑁𝑂 3 1 𝑚𝑜𝑙 𝐶𝑢 × 1000𝑚𝐿 15.8 𝑚𝑜𝑙 𝐻𝑁𝑂 3

Reaction with Nitric Acid IN THE FUME HOOD add the correct amount of acid to the volumetric flask. WEAR APRON, GOGGLES AND GLOVES. Mr Dowdy or myself must be with you for this step. Continue with procedure for Part II, Step #4 and 5.

On Friday: Divide and conquer! One or two partners prepare the standard solutions as listed on the following slides for Part I and the other prepare the brass sample for Part II.

Results From the analysis tab, do a curve fit-linear. From the analysis tab, interpolate your absorption value for the brass solution. While on that screen, try to autofit your graph into the available window. Print the screen from the file menu.

Postlab Questions You will answer these in your notebook before you write a conclusion.

Disposal & Clean-up Cu(NO3)2 solutions can be rinsed down the drain. Use test tube brush and soap to clean test tubes and volumetric flasks. Return beakers, cylinders to glass front cabinets. Return test tube racks to center cabinet at your station. Return other materials to back table.