Jan. 26-29

What happens when you chemically mix zinc and hydrogen chloride? What will be the reactant (product)?

This is the experiment I did with my group this week. The challenge was to answer the above question.

I hypothesized that since hydrogen and chlorine are already chemically bonded together and can't bond with the zinc, I figured that the hydrogen or the chlorine would escape from the system and combine with the gas in the air while the zinc would stay in the system since it's a metal.

In order to find out what the reactants will be, my group and I first considered the mass of the zinc, the beakers, and the hydrogen chloride. To measure the zinc, we just put it on a measuring scale to calculate its mass. Then, to find out the mass of hydrogen chloride, I figured that in order to do so, we must find out the change in mass when comparing the beaker's mass to the mass of the beaker and the hydrogen chloride in it. Then, I subtracted the mass of the beaker with the total mass, therefore, to find the mass of hydrogen chloride.

By finding the masses of all these variables, we figured this would be the best way to find out the total mass after the zinc and the hydrogen chloride are chemically combined together, that is, by combining the masses of hydrogen chloride and zinc before they were combined. I assumed that since hydrogen or chlorine would escape from the system, the mass would have to decrease.

However, to get an accurate result, we made sure nothing new entered or left the system to increase or decrease the mass. So, we used a trough, which has an extension cord with a cork attach to it. By capping the beaker with the cork, this can help to trap the reactants in the beaker.

So, my group and I thought of an experimental procedure. To find the volume of the reactant, we would fill a different bottle all the way with water while filling the trough with water. Then, mix the zinc and the hydrogen chloride together. But, we had to seal the beaker quickly so that the gas wouldn't escape. Keeping in mind that the tube is attached to the trough, the gas goes through an opening inside the trough. So, to collect the product, you should fill a bottle with water and tip it over right side using a lens to prevent spilling. Remove the lens once done. Then, combine the zinc and hydrogen chloride so that they will chemically react to form a new substance.

Then, gradually wait until the water level drops and then to collect the gas without it escaping, use the lens once again and flip it up.

Now, with the gas in the bottle, my group and I can test it's chemical properties to determine what the gas is. Hydrogen, for example, is flammable (think the Hindenburg), and oxygen is combustible. To determine if the gas had these properties, we lit a match to test for combustibility and flammability. Once we put the match in the container, the flame got brighter. Therefore, the gas was flammable. When the match got in contact with the gas, a sound was made. Therefore, the gas was combustible.

Also, you can find the density of the gas to determine what it is. To do so, keep in mind the beaker's mass. But, measure it again. It should have changed. Subtract the mass of the beaker from the total mass. Then, find the volume of the gas by looking at the bottle. If there is any condensation on the bottle, this indicates the amount of space it takes up. Then, you divide the mass of the reactant by the volume in which it took up the bottle to find the density. (Do this before testing the gas's properties so you can calculate its density correctly).

With these results, we concluded that since the gas was combustible and flammable, it had both oxygen and hydrogen. But, what happened to the zinc and the chloride? And how did the oxygen get in the picture? We conclude that since the air has oxygen, and since it is diatomic, it combined with H2 (hydrogen molecule) to form water. This would then make sense since the inside of the bottle had condensation on it.

Zinc Chloride

But, what happened to the zinc and the chloride? We noticed that those were left in the beaker that was capped. The zinc, I noticed, dissolved in the chlorine, and when that happened, it formed zinc chloride. But, they chemically combined together. Through this experiment, we identified the two separate reactants: H2O and ZnCl.

After this experiment, I had a hunch that I would then learn about writing chemical equations. I then thought that by combining chemical substances, I could identify the chemical composition of the reactants by writing out their chemical equations. To do so, you need to know what the beginning products consist of. Then, what the reactants consist of.

When writing chemical equations, I noticed that it was like doing Algebra. Remember this? 2(XY)=2X2Y. By using this, you use the distributive property, which is when you multiply the outer term by the inner terms. Here is an example of the distributive property in chemistry: 2(H2O)=(2H2)(O2).

I then wondered what the difference was between these: H2O2 and 2 OH. At first glance, it seemed as if H2O2 was a single compound while 2HO was two compounds. Even though they have the same elements and the same number of those elements, they are different chemical compounds. H2O2 is Hydrgen Peroxide while 2 OH are 2 OH molecules.