Rates of Reaction

A Lab Investigation

Monday 2/25/08Prep: 1. Get 30 copies of each lab handout – temp, conc, surface area & metal

type2. Set up demo of reaction of HCl & ZnClass:DMA: Schedule of Week (Pass back papers) Remind students of lab fee.1. Demo – under camera – HCl + Zn2. 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

controlAsmt: 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) ZnCl2(aq) + H2(g)

• Draw & observe the standard set up for this lab.

• Measure the zinc consumption or gas production versus time.

Data & ObservationsKeep Track of?

Mass of Metal Used for Each Trial

(1.0g max)

Amount of Acid Used for Each Trial

(10 ml max)

Temperature (50oC 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 stopper 10ml graduated cylinderGlass 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, • 2 250 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?)

Item Formula Work Answer

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.

Conclusions1. 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 1st trials and 6M for the 2nd 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.