16. Read the commentaries to the lab experiment and then comment the formulas below. Laboratory Preparation of Hydrogen
The most convenient laboratory method for the preparation of hydrogen is based on the reaction of zinc with dilute sulphuric acid. The gas is to be collected over water. Zinc’s rate of reaction can be easily controlled by regulating the rate with which sulphuric acid is added.
Z
n+H2SO4
H2+ZnSO4
The surface of pure zinc placed in a solution of dilute sulphuric acid becomes coated with a film of hydrogen, the reaction proceeds very slowly. The evolution of gaseous hydrogen cannot be observed.
Laboratory Preparation of Nitric Acid
Nitric acid may be prepared by the reaction of concentrated sulphuric acid with sodium nitrate. In the laboratory method, a mixture of sodium nitrate and concentrated sulphuric acid is heated in a glass retort. Nitric acid is boiled out of the mixture and is condensed:
NaNO3+H2SO4 = HNO3+NaHSO4
Laboratory Preparation of Hydrochloric Acid
|
Many experiments can be carried out in the laboratory of inorganic chemistry. Thus, if we want to obtain hydrogen chloride (HC1), which is often referred to as a hydrochloric acid gas, it is necessary to pour some sulphuric acid through a tube over the crystals of sodium chloride in flask. The flask is to be heated. On warming the flask, the hydrogen chloride is expelled as colourless gas with a suffoсating odour. |
It produces heavy clouds white fumes when it comes in contact with the moist air of the room. It is soluble and it cannot be collected over water as are oxygen and hydrogen. It is much heavier than the air and may be passed through a glass tube to the bottom of a bottle.
C
a(OH)2
+ 2NH4Cl
= CaCl2
+ 2NH3
+2H2O
C
H3CH2OH
H2SO4Br2
CH2
= CH2
(
) + H2O
C
u
(OH)2
= CuO
(
) + H2O
4P + 5O2 = 2P2O5
17. Answer the questions:
1. What is the laboratory method for the preparation of hydrogen based on?
Where is gas to be collected?
How can the zinc's rate of reaction be controlled?
Can the evolution of gaseous hydrogen be observed?
18. Read and catch the idea of the dialogue. Describe any lab where your practice takes place.
Hello, Jack. Haven‘t seen you for ages!
Hi, Ann! Glad to meet you again. How are you?
Fine, as always! And what about you? How do you find your new students’ life?
Generally speaking my student’s life gives me much pleasure. At last I can have enough time for my favourite subject.
You study chemistry, don’t you?
Yes, I do. It’s a difficult but very interesting science.
You’ve got much practice now, don’t you?! Do you make many experiments in the laboratories?
Certainly, yes. Practical classes are my favourite ones. Would you like to see our chemistry lab? Oh, common! It is a very interesting place. I have some minutes, so I could show you it now, if you don’t mind.
Let’s go then, if it’s not far from here.
Come in. At first sight there is much glass in the lab.
Oh, really! There are so many bulbs, flasks, tubes and pipes here. It seems to me that it is a little bit magic place…
There is nobody here, but be careful, please, as there is so much glass everywhere for the next series of experiments on the benches today.
And what are there on the shelves?
There are test-samples of different chemicals. Here you can see acids, alkalies, iron, tin, aluminium, nickel, chalk.
And what is there in the right corner?
Ah! It’s a stove. We use it sometimes for our experiments.
What is there in the big bottles?
There is distilled water, we also have an apparatus for the preparation of it. We need much distilled water.
There are so many stands and placards on the walls.
Yes, you can see photos of our staff, on the other the students do different experiments. If you noticed, we must be in a uniform during our practice not to spoil the cloths. As for me, I don’t like it, but it’s really necessary not to spoil the cloths.
Thanks, Jack! You are a nice guide.
You are welcome! Bye!
See you later!