Airbag Design Lab

Is it possible to use baking soda, NaHCO3(s), and 2.00 mol dm-3 HCl(aq) to generate a gas that will fill a zip-lock bag and act as an air bag?

Objectives:

1. To determine if baking soda and hydrochloric acid can create a suitable air bag

2. To determine the volume of hydrochloric acid needed

Hypothesis:

If given baking soda and 2.00 mol dm-3 HCl(aq), it is possible to create an effective airbag, if the correct quantity of each reactant is put into the reaction in order to create a distinct quantity of products. If an incorrect quantity was added, two possibilities can occur; a limp airbag or the airbag will be too firm and explode.

In this investigation the limiting reagent is the 2.00 mol dm-3 HCl(aq) as oppose to the baking soda due to the dangerous nature of hydrochloric acid, in case of the airbag exploding if there is an excess of this compound the victim would possibly suffer burns and poisoning, while if there is an excess of baking soda the victim would not suffer additional injuries.

In order for the reaction to take place only when needed, the baking soda will rest in the Ziploc bag while the hydrochloric acid will be added when needed.

In order to determine the amount of reactants needed, the volume of the ziploc bag where the reaction will take place to create an airbag must be known. The ziploc bag will first be filled with water then dumped into a graduated cylinder in order to determine the volume of the bag. The volume of the bag will then allow the calculations of the amount of baking soda and hydrochloric acid needed to create a reaction. Once the volume of the Ziploc bag is known, the atmospheric pressure as well as the water vapour pressure as well as the temperature must be measured in order to determine the amount of pressure present while the reaction is ongoing.

Once the above values; volume, temperature, pressure are known it is possible to determine the number of moles of carbon dioxide that will form in the reaction using the ideal gas law which is PV=nRT, R being the constant. Then using the chemical equation; NaHCO3+HCl–> H2O+CO2+NaCl we are able to observe that the number of moles remain consistent through all of the products and from the reactants. Once the number of moles of hydrochloric acid needed is determined, the volume of the HCl must be determined from its 2.00 mol concentration. The volume of HCl must then be subtracted from the volume of the Ziploc bag, to determine the volume that is left for the baking soda to occupy. With the new volume, the ideal gas law will once again be used in order to determine the number of moles of baking soda needed. The moles of baking soda will then be converted into grams in order to add into the bag. Once the calculations are all complete, the reactants are able to be added into the airbag.

Variables:

Manipulated Variable: The manipulated variable in this experiment is the volume of the zip-lock bag. In response to the volume of the Ziploc bag, the same volume of Carbon Dioxide will be produced. Within the given volume of the Ziploc bag, the following can be determined the larger the bag the higher the number of moles of HCl and baking soda will be needed to ensure that the entirety of the bag is filled with Carbon Dioxide. Therefore the volume is capable of changing the variables a result of the experiment.

Responding Variable: The responding variable in this experiment is the number of moles of carbon dioxide, water, and sodium chloride solution that forms. Like previously stated if the manipulated variable is of a greater value, the responding variables will be of a greater value.

Controlled Variable: The controlled variable in this experiment are temperature and pressure. These two factors are consistent throughout the experiment, if the pressure and temperature were not consistent the results would have changed substantially, and the proper quantities would not be able to be determined in order to obtain the products.

Apparatus and Materials

Materials

Apparatus

* 2.00mol dm-3 HCl(aq)

* Baking Soda

* Zip-lock plastic bag

* Thermometer (�0.1�C)

* 1000mL graduated cylinder (�0.1mL)

*Safety precaution: When performing the experiment be sure to put on safety goggles.

Procedure/Method:

Preparation for the experiment: Construct two tables; qualitative data and quantitative. (as shown below)

Be sure to record the uncertainties in the data collected in order to later address possible sources of error if the expected outcome does not occur.

1. Measure the volume of the ziploc bag by filling it completely up with water (make sure there are no air bubbles!) and pouring it into a large 1000 mL graduated cylinder.

2. Record the volume in your data table.

3. Record the given temperature and pressure that the teacher provides you in the data table.

4. Use the ideal gas law to find the moles of carbon dioxide present (PV=nRT, you are given temperature, pressure, R is a constant, you know the volume, so now you can find n)

5. Using the balanced chemical reaction of baking soda and hydrochloric acid (NaHCO3+HCl–> H2O+CO2+NaCl) it is evident that the mole ratio between carbon dioxide and hydrochloric acid would be one-to-one.

6. Using the moles of HCl needed, figure out the volume needed of HCl from its 2 mol concentration.

7. Subtract the volume of HCL from the original volume of the ziploc that was measured in the beginning (this is because the HCl will occupy the space of the bag once it is added)

8. Using the ideal gas law again, plug in the new subtracted volume into the formula to figure out the moles of NaHCO3.

9. Convert moles of baking soda into grams. Record the amount of baking soda needed.

10. Mix the ingredients according to the recorded volume and amount of HCl and NaHCO3 that was required. Be sure to add the baking soda first then the hydrochloric acid.

11. Have a partner QUICKLY close the zip-loc bag to prevent air from escaping. Watch the bag inflate.

Qualitative Observations – Data Table I

Variable

Observations

Baking soda

* White

* powdery

Hydrochloric Acid

* transparent

* colourless

* odourless

* liquid

Sodium Chloride solution

* opaque

* white

* not homogenous

Water

* transparent

* colourless

* odourless

* liquid

Carbon Dioxide

* clear transparent gas

* present every where

Quantitative Observations – Data Table II

Variable

Value

Volume of Ziploc bag

750mL

Room Temperature

20

Atmospheric Pressure

=76.15cm/Hg

=101.52kPa

Pressure exerted in the experiment (atmospheric pressure-water pressure)

Water pressure=2.34kPa

101.52kPa-2.34kPa

=99.18kPa

Moles of CO2

(PV=nRT)

PV/RT=n

(99.18)(.750L)/(8.314)(293k)=n

n=0.030536

Concentration of Hydrochloric acid (HCl(aq))

n=cV

n/c=V

0.030536/20.015268L

15.268mL

Volume of Ziploc bag-volume occupied by HCl

.750L-0.015268L

=.734732L

Moles of Baking Soda (NaHCO3)

(PV=nRT)

PV/RT=n

(99.18)(.734732L)/(8.314)(293k)=n

�0.02991406 mol-1

Mass of Baking Soda (NaHCO3)

m=(n)Mr

0.02991406 mol-1 x 84.0059 g/mol-1

=2.5129579g

2.5130 g

Conclusion:

The following execution of the experiment proved that it is possible to construct an effective airbag out of hydrochloric acid and baking soda. The following was done in the experiment.

The amount of reactants needed was determined by finding the volume of the ziploc bag where the reaction took place. The ziploc bag was filled with water then dumped into a graduated cylinder to determine the volume of the bag. The volume of the bag allowed the calculations of the amount of baking soda and hydrochloric acid needed to create a reaction. The atmospheric pressure as well as the water vapour pressure as well as the temperature was measured. Once the volume, temperature, pressure were known the number of moles of carbon dioxide that formed in the reaction was found using the ideal gas law which is PV=nRT, R being the constant.

The using the chemical equation; NaHCO3+HCl–> H2O+CO2+NaCl showed that the mole to mole ratio between all of the reactants and products were the same. The number of moles of hydrochloric acid needed was determined, and from that the volume of the HCl from its 2.00 mol concentration was found. The volume of HCl then was subtracted from the volume of the Ziploc bag, to determine the volume that is left for the baking soda to occupy. With the new volume, the ideal gas law once again was used in order to determine the number of moles of baking soda needed. The moles of baking soda then was converted into grams to add into the bag. Finally, the calculations were all complete, and the reactants are added into the airbag.

The firm effective airbag was achieved due to the exact amount of reactants needed in order to create the reaction, if the amount of reactants that were added were different then the following experiment would not have been as effective and would have resulted in either a limp airbag, or one that exploded from too high of a density due to too much compounds being present within, and too little volume.