Rates of Reaction A Lab Investigation

Monday 2/25/08 Prep: 1.Get 30 copies of each lab handout – temp, conc, surface area & metal type 2.Set up demo of reaction of HCl & Zn Class: DMA: Schedule of Week (Pass back papers) Remind students of lab fee. 1.Demo – under camera – HCl + Zn 2.Determine balanced chemical equation. 3.How measure rate of reaction? 4.What factors might influence rate of reaction? 5.Choose which pair will investigate which factor – every 4 tables will choose a different factor. 6.Write hypothesis, manipulated & responding variables, variables to control Asmt: Draft Procedures (Include at least 5 different levels & repeat the experiment)

How can we measure the rate of a reaction? In math: rate = distance/time In life: rate = anything changing/time How can we measure the rate of the reaction: Zn (s) + 2HCl (aq)  ZnCl 2(aq) + H 2(g) Draw & observe the standard set up for this lab. Measure the zinc consumption or gas production versus time.

Data & Observations Keep Track of? Mass of Metal Used for Each Trial (1.0g max) Amount of Acid Used for Each Trial (10 ml max) Temperature (50 o C max, don’t try to be exact) Time Elapsed for Each Trial (5 minute max) Volume of Gas Produced for Each Trial (10ml max) Observations for Each Trial

Standard Reaction Rate Set Up beaker Test-tube Rubber tubing One-hole stopper10ml graduated cylinder Glass tube

Materials Available 1 M HCl (several liters) 6 M HCl (500 mL) Distilled water (several liters) 1 cm2 Al foil squares (lots of these per class) Mossy Zn Mg ribbon Fe filings (20,30,40&50mesh) Sn pieces Cu wire pieces Marble chips for waste bucket Timing devices (stopwatch.com) Hot plates Ice Beakers for water baths Thermometers Each pair will receive: 10 mL graduated cylinder, mL beakers, 1 test tube, 1 eye dropper, rubber tubing (30cm), one-hole rubber stopper

What factors might influence the reaction rate? Acid Concentration Type of Metal Used Size of Pieces (Surface Area) Temperature

Pre Lab Assignment: Question: “What is the effect of _____ on the reaction rate of hydrochloric acid and a particular metal?” Hypothesis: (If, then, because) Manipulated Variable: Responding Variable: Controlled Variables: Materials: Diagram: Validity Measure: (Calibrate? Prevent Contamination?) Procedure: (at least 5 levels, repeated at least 2x)

Experimental Controls? Amount of Acid? Strength of acid? Amount of Metal? When will you stop the trial?

Analysis (1 of 3) Calculations: Diluted Concentration = (Acid M)*(ml acid/total ml) Rate = amount of hydrogen gas/time Averages of Repeated Trials (Temperature?) ItemFormulaWorkAnswer Concentration of Sample 1 Original M (ml acid/ total ml) Rate of sample 1 bubbles or ml of H2 / time

Analysis (2 of 3) Graph using Excel: X – axis is your manipulated variable Y- axis is the average of your repeated rate of gas produced/time Use XY scatter graphs for Concentration, Temperature & Size (mesh) Use Bar graphs for Types of Metal Temperature (2 XY scatter graphs good)

Analysis (3 of 3) Sources of Error: At least 3 real observed reasons why the reaction rate results are not perfect.

Conclusions 1. Restate your hypothesis and evaluate its accuracy. 2. Use low and high values from your experimental results to justify your conclusions. 3. Explain how your results compare to the collision theory. 4. Explain how the results of this investigation can be applied to a real world situation beyond the lab. Look for examples in Chapter 22.

Suggestions Rate vs. Temperature Students will need 1 M HCl, water baths, thermometers, and heating/cooling equipment. Mossy Zn is the best metal for this experiment. Rate vs. Concentration Students will dilute 1 M HCl with distilled water. Mossy Zn or Mg ribbon work best for this experiment. Rate vs. Surface Area Students will need 6 M HCl for this experiment or else the iron filings react too slowly. Rate vs. Type of Metal Students will need 1 M HCl for the 1 st trials and 6M for the 2 nd and access to Mg, Zn, Fe, Al, Cu and Sn. Size/mass of metal is a controlled variable that students frequently neglect to include in their experimental designs.