Limiting and Excess Reagents

First Objective Your first objective of this lab begins before lab. You should come to lab with the balanced chemical equation, table finished (pg.125), and #4. Make sure that you check your values with me, either via email or before lab.

Assigned Data to Collect Each lab group will determine a different section of the lab data. The data will then be shared after it is collected. Group A: (1mL/6mL) Group B: (2mL/5mL) Group C: (3mL/4mL) Group D: (4mL/3mL) Group E: (5mL/2mL) Group F: (6mL/1mL)

Experiment Each lab group should follow these directions with the assigned volumes. Collect 6 small test tubes and tongs Label 1,1a,1b,2,2a,2b A and 2 should be pyrex (heated later) and wipe clean of fingerprints and don’t touch again Weigh 1 and 2

Test tubes 1 and 2 Add assigned volumes of Cu(NO3)2 and KI in test tubes 1 and 2 Record any observations Use kimwipe to hold top of test tube and also to tap bottom on test tube to mix chemicals Set in test tube rack for 5 minutes to fully react Centrifuge the test tubes to collect solid for 5 minutes

Test tubes 1 and 2 Remove test tubes with kimwipe, gently to insure that the precipitant is not disturbed Supernatant should be clear brown-green and solid gray precip. At bottom of test tubes Put in test tube rack Gently draw off supernatant with disposable pipet (read directions is lab book!! #6 pg120)

Test tubes 1 and 2  1a,1b,2a,2b Place half of the supernatant from test tube 1 into test tube 1a, and the other half into test tube 1b Place half of the supernatant from test tube 2 into test tube 2a, and the other half into test tube 2b Set to side for further testing later

Test tubes 1 and 2 Wash precip. by adding ~3mL methanol (MeOH) to test tube 1 and 2. Add the same to both test tube Use kimwip to gently shake tubes so precip starts to cloud the solution. Place back in centrifuge for 5 minutes Supernatant should be clear again

Test tubes 1 and 2 Remove supernatant without disturbing precip Supernatant this time will not be tested Can use same pipet Discard supernatant into waste container Place test tubes 1 and 2 in 100mL beaker Write name on beaker Place in oven for at least 20 mins to dry Test tubes must cool before weighing

Test tubes 1a,1b,2a,2b While waiting for test tubes 1 and 2 to dry Add 1mL Cu(NO3)2 solution to test tubes 1a and 2a Record any observations Add 1mL KI solution to test tubes 1b and 2b

Test tubes 1 and 2 After test tubes have been in oven at least 20 mins, remove and place in desiccator to cool for at least 10 minutes Desiccator keeps precip from absorbing moisture Weigh each test tube once cool Calculate mass precip in each tube Give to instructor to post for whole class Make sure you have all the data (from all lab groups) before leaving class

% error vs % yield % error = [(actual-theoretical)/theoretical)]*100 % yield = (actual/theoretical) *100