Experiment 7: ATMOSPHERIC GASES _ . j,
One of the driving forces for double-displacement reactions is formation of a gas as a product. In this experiment, I J.
you will study double-displacement reactions involving a bicarbonate, a sulfite, and a nitrite and a strong acid as a ‘i
means of forming Co2, $02, and No2. Oxygen gas will be generated by the decomposition of hydrogepperoxide
(H202), which is catalyzed by iron (III) chloride. The chemical properties of oxygen, Co2, So2, and No2 will then
be studied.
1. Omen
The purpose of this part of the experiment is to demonstrate some of the chemical reactions by which oxygen can be
produced, and to examine some of its chemical properties. You should keep in mind most reagents releasing oxygen
are powerful oxidizing agents, which react violently with oxidizable materials. Hot potassium chlorate, for example,
can react explosively with charcoal, a wood splint, with scraps of paper. or similar combustible materials.
A. Preparation of Oxygen H 1C .2 5 C =3- + H LG I
l. Fit a 125 mL Erlenmeyer flask with a one-hole rubber stopper and gas delivery tube. The delivery tube
should be arranged so that the oxygen gas produced will displace water from wide mouth bottles. Your
instructor will show you how to assemble the apparatus.
2. Add 75-80 mL of 3% hydrogen peroxide to the Elusive… Then add two heaping spatulas of solid iron (III)
chloride. Swirl the reaction mixture gently. and ilifiiiaifii the oxygen gas produced. Have several (4 or 5)
bottles ready, so that you can change bottles only}; it; n- nhmrt losing oxygen. Cover each bottle immediately
after it is filled.
3. When you are finished, put the spent, but very aridm, solution in the bucket labeled “Waste iron (III)
chloride and peroxide”.
B. Reactions with Oxygen
Oxygen readily combines with other elements. Some of the common reactions are demonstrated in the
I t 1 . “1 “in”
expenmensbe ow f: a: . __,, x. (.0 ,2.
1. Carbon: Using a deflagrating spoon, lower glowing charcoal into a bottle of oxygen. Then set a wood
splrnt afire, and blown out. While the splint rs still aglow, lower it into a bottle of oxygen. The product
formed rs carbon dioxide.
2. Sulfur: Do this experiment in the hood. Using a deflagrating spoon, lower burning sulfur into a bottle of
oxygen. Very carefully smell the gases ermtted from thrs reaction. Sulfur dioxide and sulfur trioxide are
the most likely products. t- O
S, ~ 1. -e
3.. Iron: Using forceps, heat some steel wool until it is red hot, and then lower it into a container of oxygen.
record yourzpbservgaflons. To deduce the formula of the product, you should note that iron can be oxidized
Carbon dioxide will be produced by the reaction of sodium bicarbonate with hydrochloric acid. The reactions
between Co2 (g) and water and Co2 (g) and aqueous calcium hydroxide will be examined.
1. Place about 2 g (1/2 teaspoon) of sodium bicarbonate, NaHCo3 . into a bottom comer of a 1 pint hea
duty leloc bag- H a HCO 3 + (Tfig e (Jail r mtg,
2. Fill a plastic pipet with 6 M HCl (caution). Place the pipet into the bag, smooth it to remove as much air as
possible. and seal the bag. Be careful not to press against the pipet.
3. Expel the HCl from the pipet onto the sodium bicarbonate. The bag will fill with Co2. I
4. Expel the air from a clean pipet, and carefully insert it into the gas-filled bag at one corner of the seal. Do
not open the bag more than absolutely necessary. Taking care not to touch the liquids or solids in the bag,
insert the pipet deep into the bag and release the bulb so that the pipet fills with gas. Remove the pipet and
reseal the bag.
5. Put 1 mL of distilled water into a clean test tube and check the pH. Bubble the carbon dioxide into this
water. Measure the pH of the resulting solution.
6. Obtain another pipet full of carbon dioxide. and bubble it into 1 mL of Ca(OH)2 (aq). Record your 54) 314.73″
observations. ‘ g;
7. Place the used bag in the waste bucket labeled *’ more bags. I
3. Sulfur Dioxide
Sodium sulfite will be reacted with sulfuric acid to produce sulfur dioxide gas. Note that sulfur dioxide gas is
readily oxidized in air to form 803 (g). The reaction between SO3 (g) and water will be studied.
D 1. Place about 2 g (1/2 teaspoon) of sodium sulfite, Na2803, into a bottom corner of a 1 pint heavy-duty
Ziploc bag.
D 2. Fill a plastic pipet with 6 M H2SO4 (caution). Place the pipet into the bag, smooth it to remove as much air
9 . as possible, and seal the bag. Be careful not to press against the pipet.
3. Move to a fume hood. Expel the H2804 from the pipet onto the NaZSO3. The bag will fill with $02.
3 4, Expel the air from a clean pipet, and carefully insert it into the gas-filled bag at one corner of the seal. Do
5 not open the bag more than absolutely necessary. Taking care not to touch the liquids or solids in the bag,
insert the ptpet deep Into the bag and release the bulb so that the pipet fills with gas. Remove the pipet and
9 reseal the bag.
5 7. Put 1 mL of distilled water into a clean test tube. Bubble the sulfiu dioxide into this water. Measure the
a pH of the resulting solution.
B 8. Place the used bag in the bucket labeled “waste bags”.