GRIFFIN EDUCATION working with
EDU-LAB and The RADMASTE Centre
UNIT C1a TOPIC 6 MAKING CHANGES
PREPARATION AND TESTING FOR HYDROGEN
REQUIREMENTS
Apparatus:
Chemicals:
1 x comboplate®; 1 x silicone tube with U-bend (U-tube); 2 x plastic microspatulas;
1 x propette; 1 x lid 1; 1 x gas collecting tube with lid; 1 x 2 ml syringe;
matches or toothpick splints; 1 x plastic cup; prestik.
Zinc powder (Zn(s)); Hydrochloric acid (HCl(aq)) [5.5 M];
Anhydrous copper(II) sulphate powder (CuSO 4(s));Tap water.
PROCEDURE
1.
2.
3.
4.
5.
6.
7.
Use the spooned end of a plastic microspatula to place 2 level spatulas of zinc powder into well F1. Seal
well F1 with lid 1.
Connect the straight end of the U-tube to the tube connector on lid 1.
Remove the lid from the gas collecting tube. Attach a small piece of prestik to the outer end of the lid
and stick the lid inside the bottom of a plastic cup or similar container.
Fill half of the plastic cup with tap water.
Fill the gas collecting tube to the brim with water.
Place the tip of one of your fingers over the mouth of the gas collecting tube and invert it (turn it upside
down), making sure that no air bubbles remain in the tube.
Keeping your finger in place, lower the inverted tube into the water in the plastic cup.
Do not remove your finger until the mouth of the tube is below the level of the water in the cup.
8.
9.
Lower the U-tube into the plastic cup. The bent end must be on the bottom of the cup next to the
mouth of the gas collecting tube.
Fill the syringe with 0.5 ml of 5.5 M hydrochloric acid. Fit the nozzle of the syringe into the inlet on lid
1.
Testing for Hydrogen
Page 1 of 5
If you have followed steps 3 to 9 correctly, then your set-up should look like that in the diagram
above.
10.
11.
12.
13.
14.
15.
16.
17.
Slowly add about half of the acid dropwise to the zinc powder in well F1. (See Question 1)
Wait for a few bubbles to appear in the water in the plastic cup. Carefully place the gas collecting tube
over the bent end of the U-tube. (See Question 2)
Add the remainder of the acid to the zinc and collect the gas in the gas collecting tube. (See Question 3)
When there is no more water left in the gas collecting tube, carefully lift the tube away from the Utube. Push it firmly into the lid at the bottom of the plastic cup. Never lift the gas collecting tube
above the water level in the cup.
Carefully twist the tube so that the tube and its lid are dislodged from the prestik. Remove the sealed
gas collecting tube from the cup and put it upside down on the desk next to you.
Light a match. Wait until the flame is small, then quickly remove the lid from the gas collecting tube.
Hold the tube horizontally and quickly place the flame just inside the mouth of the tube. (See Questions
5 and 6)
Use the narrow end of a clean microspatula to add a few grains of white anhydrous copper sulphate into
the clear liquid formed at the mouth of the gas collecting tube. (See Question 7)
Rinse the comboplate® thoroughly with water.
Q 1.
QUESTIONS
What do you observe in well F1 when the hydrochloric acid is added to the zinc powder?
Q 2.
Why is it necessary to let a few bubbles emerge from the U-tube before collecting the gas in the gas
collecting tube?
Q 3.
What happens to the water in the gas collecting tube as the bubbles of gas enter the tube?
Q 4.
What is the term used to describe what happens to the water in Question 3?
Q 5.
What happens when the flame of the match is held inside the mouth of the gas collecting tube?
Q 6.
Can you see anything on the inner rim of the gas collecting tube where the reaction occurred?
Q 7.
Is there a change in the appearance of the white copper sulphate?
Q 8.
Write down a word equation for the chemical reaction in well F1 between hydrochloric acid and zinc.
Q 9.
What property of the gas collected made it necessary to hold the gas collecting tube upside down?
Q10.
Why was there a “pop” sound when the lighted match was brought to the mouth of the gas collecting
tube?
Q11.
What product was formed by the chemical reaction mentioned in Question 10? Give a reason for your
answer.
Q12.
Write down a word equation for the chemical reaction referred to in Questions 10 and 11.
Q13.
What does the term “anhydrous” mean?
Q14.
Why did the white copper sulphate change colour and what is the name of the product formed?
Q15.
Write down the balanced chemical equation for the reaction occurring in well F1 between zinc and
hydrochloric acid.
Q16.
Write down the balanced chemical equation for the reaction occurring in the gas collecting tube when
the gas produced was tested with the lighted match.
Q17.
Write down the balanced chemical equation for the reaction of the anhydrous copper sulphate with the
clear liquid produced in the gas collecting tube.
Q18.
Write down the name of the other product formed when zinc reacts with hydrochloric acid.
Testing for Hydrogen
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PREPARATION AND TESTING FOR HYDROGEN
TEACHER GUIDE
1. Chemicals
All of the required chemicals are listed in the worksheet. Tap water is also needed.
2. Equipment
Most of the apparatus required can be found in an Advanced Microchemistry Kit. A plastic cup and prestik are
also needed.
3. Hints
A plastic cup has been used here, but other suitable containers can be used into which the inverted gas
collecting tube can be placed.
Add the 5.5 M hydrochloric acid (HCl(aq)) slowly to the zinc powder (Zn(s)), otherwise the vigorous bubbling in
well F1 may force the solution up through the silicone tube (pvc in older kits) with the U-bend. Add 0,2 ml of the
acid first to purge the system of air. Thereafter, place the gas collecting tube over the outlet of the U-tube in
the plastic cup, and add the remaining acid slowly.
When removing the gas collecting tube from the set-up, push the tube firmly into the lid at the bottom of the
plastic cup. You do not need to screw the tube into the lid. Gently lift the tube with the lid out of the cup. The
lid does not adhere to the prestik at the bottom of the cup if the procedure is carried out correctly.
4. Cautions
Please remember the following cautions and inform your students of all safety hazards:
Hydrochloric acid is corrosive. If any acid is spilt on the skin, the affected area must immediately be
rinsed with copious amounts of water. Severe burns must receive medical attention.
Never point a propette or a syringe containing acid upwards. A momentary lapse of concentration can
result in a nasty accident. If any acid is squirted into the eye, immediately rinse the eye out under running
water. Always have a dilute solution of sodium hydrogencarbonate (household baking soda), or milk close by
to apply to the injury. These substances will help neutralise the acid in the eye. The patient should be
referred to a doctor.
Do not allow anyone to bring a flame near the comboplate®. The hydrogen gas generated in well F1 is
highly explosive. Ensure that the comboplate ® is moved away from all sources of flames before the test for
hydrogen is completed.
Never allow the learners to play with matches. Treat any burn with cold running water or ice, and seek
medical assistance where necessary.
Testing for Hydrogen
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5. Model Answers to Questions in the Worksheet
It is recommended that learners write down all of the questions and answers in their workbooks. If this is done,
then the answers to questions do not have to be in full sentences. If the learners do not copy the questions into
their workbooks, then answers should be written in full sentences. Note that some of the questions can only be
answered by learners in higher grades. Word equations can be written instead of chemical equations where
required.
Q1.
A1.
What do you observe in well F1 when the hydrochloric acid is added to the zinc powder ?
Bubbles are given off vigorously as a gas is produced.
Q2.
Why is it necessary to let a few bubbles emerge from the U-tube before collecting the gas in the gas
collecting tube ?
Before the reaction occurred, the silicone tube was filled with air. The first few bubbles which
emerged were therefore air.
A2.
Q3.
A3.
What happens to the water in the gas collecting tube as the bubbles of gas enter the tube ?
The water is pushed out of the gas collecting tube.
Q4.
A4.
What is the term used to describe what happens to the water in Question 3 ?
The downward displacement of water.
Q5.
A5.
What happens when the flame of the match is held inside the mouth of the gas collecting tube ?
A popping sound is heard as the gas in the tube ignites explosively.
Q6.
A6.
Can you see anything on the inner rim of the gas collecting tube where the reaction occurred ?
Yes, a clear liquid has formed.
Q7.
A7.
Is there a change in the appearance of the white copper sulphate ?
Yes, the white copper sulphate becomes blue.
Q8.
A8.
Write down a word equation for the chemical reaction in well F1 between hydrochloric acid and zinc.
zinc(s) + hydrochloric acid(aq)  hydrogen(g) + zinc chloride(aq)
Q9.
A9.
What property of the gas collected made it necessary to hold the gas collecting tube upside down ?
Hydrogen is less dense than air. By holding the tube upside down, the gas was less likely to escape.
Q10.
Why was there a “pop” sound when the lighted match was brought to the mouth of the gas collecting
tube ?
Hydrogen reacts explosively with the oxygen in the air when ignited.
A10.
Q11.
A11.
Q12.
A12.
What product was formed by the chemical reaction mentioned in Question 10 ? Give a reason for your
answer.
Water. This was shown when the white copper sulphate crystals became blue in the liquid formed
on the inner rim of the gas collecting tube.
Write down a word equation for the chemical reaction referred to in Questions 10 and 11.
hydrogen(g) + oxygen(g)  water(l)
Testing for Hydrogen
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Q13.
A13.
What does the term “anhydrous” mean ?
“Anhydrous” means “without water”.
Q14.
A14.
Why did the white copper sulphate change colour and what is the name of the product formed ?
The white copper sulphate reacted with water and formed blue copper sulphate pentahydrate.
Write down the balanced chemical equation for the reaction occurring in well F1 between zinc and
hydrochloric acid.
Q15.
Write down the balanced chemical equation for the reaction occurring in well F1 between zinc and
hydrochloric acid.
Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2(g)
A15.
Q16.
A16.
Q17.
Write down the balanced chemical equation for the reaction occurring in the gas collecting tube when
the gas produced was tested with the lighted match.
2H2(g) + O2(g)  2H2O(l)
A17.
Write down the balanced chemical equation for the reaction of the anhydrous copper sulphate with the
clear liquid produced in the gas collecting tube.
CuSO4(s) + 5H2O(l)  CuSO4.5H2O(s)
Q18.
A18.
Write down the name of the other product formed when zinc reacts with hydrochloric acid.
Zinc chloride.
Testing for Hydrogen
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