Henry Cavendish Experiment

Apparatus / Materials:Pneumatic (gas-collecting) trough with hose and stopper250 ml Erlenmeyer flaskTest tube (sizes vary)Mossy ZincScupula1 M HClWood splintFlame (Bunsen burner)

SAFETY: Wear safety goggles over your eyes at all times throughout the lab until instructed by your teacher to

remove them. Wipe up any water spills immediately. Warn others immediately. Tilt the test-tube away from anyone before testing the gas with the flame. Dilute and rinse HCl down sink, with water running. Dispose of zinc in beaker provided by the teacher. Do NOT throw burning or glowing wood splints into the garbage can. Dip the end in water.

PROCEDURE:

1) Place a test tube into the bottom your pneumatic trough.2) Fill your pneumatic trough about 2/3 full with water so that test tube is covered. Be careful to

keep the rubber stopper inside the trough so as not to spill the water.3) After setting up apparatus, use scupula to transfer 1 full scoop of mossy zinc into your 250 ml

Erlenmeyer flask.4) Have your teacher pour 1M HCl into your flask. Touch the bottom of the flask to gauge the initial

temperature. Observe the initial colour of the HCl solution and zinc.5) Return to your desk and insert the rubber stopper from the pneumatic trough apparatus into the

flask. Allow bubbles to escape for about 15 seconds before collecting the gas so that air in tube is displaced by the new gas.

6) Collect gas by inverting the test tube filled with water over the hole where gas is bubbling out.

7) Have your partner light a wooden splint and carefully bring it to your desk. Once the tube is filled with the gas produced, cover it with your hand/thumb. Move your thumb/hand away as you bring the flame to the mouth of the test tube. Do NOT point the tube toward anyone including yourself.

8) Observe the temperature of the flask and colour of the products.9) Dilute and rinse flask, pouring diluted acid down the sink and dispose of zinc and other solids into the designated

beaker. Dry apparatus and return to the original location.

Discussion Questions:

1) List 3 safety precautions taken in this lab.I wore safety glasses, my hair was tied up and we cleaned up some water that we spilled.

2) What changes did you observe in your reactants? I.e. what were some observations of new products?When the Zinc was mixed with the HCL it started bubbling in the Erlenmeyer’s flask.

3) a. How did the temperature change?We waited a while before the two reacted together and when we felt the bottom of the flask you could definitely tell that it was a lot warmer.

b. Look up the definitions, was the lab endothermic or exothermic? Explain your reasoning. Endothermic – Absorbing energy by heatExothermic – Releases energy by light or heatI think that this experiment is a bit of both. Exothermic since the HCL in the Erlenmeyer’s flask was warm the gas was then being released into the test tube.

4) Write out the formula for the chemical equation and balance it.

Zinc + hydrochloric acid produces Hydrogen gas + zinc chloride

Zn + HCL = H(2) + ZnCl Zn + HCL(2) = H(2) +ZnCl

(x2)

5) Look up Synthesis, Decomposition, Single Replacement, and Double Replacement Reactions. What type of reaction is this? Explain. Synthesis Reaction – When multiple reactants combine to form a single product (exothermic)Single Replacement Reaction - One element replaces another element in a compoundDouble Replacement Reaction – Where two compounds react, where the positive ion (cations) and the negative ion (anion) switch places forming two new compounds.This experiment was a synthesis reaction since the energy was being released into the test tube.

6) How did the change in surface area of the zinc affect the reaction rate? Which reacted faster?The more surface area there was the faster the reacted to HCL.

7) How did the change in the concentration of HCl affect the reaction rate? Which reacted faster (1 M or 3M)?The 3M reacted with the Zinc a lot faster than the 1M because the concentration was higher. We saw it happen with the first demonstration.

••• Please self -evaluate prior to handing in. •••Prescribed Learning

OutcomeWhat I (the teacher)

am looking for3 points 2 points 1 point

□ Use appropriate personal protective equipment and procedures.

I should see hair tied back, clear work area, no loose clothing, Protective eye wear at all times!

Yes I use personal protective equipment

for the entire lab

I use personal protective equipment

for most of the lab

I need a few reminders to use protective

equipment

□ Use proper techniques for handling and disposing of lab materials.

I should see no horse play during lab, Clean up area(desk and sink) when finished. Heavy metals disposed of correctly.

Yes I use proper techniques

Yes I clean up our work area

I use proper techniques and clean up our work

area but need reminders to do it

I need a few reminders for proper techniques I did not clean up our

work area

□ Identify a variety of dangers in procedures

I have read over the procedure and I am prepared i.e. I know what is going on.

Yes I am prepared to actively participate. I read and understood

the lab before starting.

I need reminders of what to do next. I need

to keep asking others or the teacher for help

I have not read the procedure

I am not following the procedure