CHEMISTRY IN CONTEXT
LAB 8: METALS WITH ACIDS, PAGE 1
CYCLE 5
NAME
Transition Metals: the Acid Reactions
Written by: Margaret C. Cannady
Intended for Publication, All Copyrights Reserved
PRE-LAB DISCUSSION:
We have discussed several characteristics of the transition metals. Recall the following:
1)
Transition metals are EXCELLENT conductors of heat and electricity. Good
examples include W (tungsten), the element burned in a traditional filament light
bulb, Cu (copper), the metal used most often in electrical wiring, and Fe (iron),
the heating element on your stoves and composition of many old-style frying pans
and skillets.
2)
Also, just about EVERY transition metal will rust. That is to say that it will
combine with oxygen to form an oxide of itself. Imagine how metal screws, car
bodies, and even the good silver that your parents have at home all eventually
tarnish or form a dull coat of another substance on their surface. This substance is
FeO if the original substance was iron or Ag2O if the original substance was
mom’s good silver.
Today, we will examine one additional characteristic of the transition metals. Namely, in PURE
elemental form (i.e. when they are by themselves and NOT bound to anything else), they react
with acids (like HCl, aka hydrochloric and H2SO4, aka sulfuric). The reaction of acids with
metals produces a salt (i.e. solid powdery substance) and hydrogen gas. Hydrogen gas is
EXTREMELY flammable. Originally, blimps, once called Zeppelins, were filled with hydrogen
gas. Less dense that air, the hydrogen gas would enable the large airships to elevate and float.
However, after the infamous Hindenburg disaster on May 6, 1937, the hydrogen gas was
substituted with helium, an inert, unreactive, and nonflammable gas. A description of the
disaster and video clip can be viewed here.
Some important safety reminders:
1)
You will observe STANDARD PRECAUTIONS today. This includes goggles
and lab coat during the ENTIRE LAB. Points will be deducted from your lab
grade if Mr. Adams observes you WITHOUT these items on. These are
especially important because you will be encountering open flame. Girls with
long hair should pull their hair back and secure it AWAY from open flame.
2)
Hydrochloric acid is a strong acid. AVOID ALL CONTACT WITH SKIN! If
you experience contact, you will FIRST get an itching sensation. If this happens,
let Mr. Adams know and THEN sprinkle some baking soda on the wound. Rub it
carefully into the spill spot and rinse with PLENTY of water after about a minute.
CHEMISTRY IN CONTEXT
LAB 8: METALS WITH ACIDS, PAGE 2
CYCLE 5
APPARATUS/MATERIALS:
3 medium-sized test tubes
test tube rack
test tube holder
6M hydrochloric acid (HCl)
zinc metal
wooden splint
NAME
1 rusty nail
iron filings/powder
digital balance
PROCEDURE:
Part A: The Hydrogen Bark
1) Obtain one piece of zinc metal. Note the physical
appearance of the zinc reactant (one of two substances
that are supposed to react) describing its physical
characteristics (i.e. color, texture, appearance, etc.).
Record your observations in the table in the
Data/Observations section.
2) Add 5mL of concentrated HCl to a clean medium-sized
test tube. (NOTE: Be VERY careful when pouring!)
Place the test tube in your test tube rack. Note the
physical appearance of the HCl. Record your
observations in the table in the Data/Observations
section.
3) Place one piece of zinc metal in the test tube with the
acid. Using the test tube holder, invert a second test tube
over the mouth of the first test tube where the reaction is
occurring (see picture to the right). Hold in place for 30
seconds to 1 minute.
4) Note what is happening in the reaction test tube with the
zinc and hydrochloric acid. LATER, but NOT now,
because you need to hold the inverted test tube in place
for 30 seconds to 1 minute, you will record your
observations in the Data/Observations section. While one lab partner is holding the
inverted test tube in place, the other partner will go to the Bunsen burners and light a
wooden splint and return to the lab station holding the burning splint (Don’t let it go
out!).
5) Then, move the upside down test tube away from the reaction test tube keeping it upside
down, and QUICKLY insert the lighted splint into the mouth of the test tube which had
been inverted. A “pop” known as a “hydrogen bark” indicating the presence of hydrogen
gas should be heard as the gas QUICKLY combusts inside the test tube. Wait patiently,
and if it does NOT occur, repeat the procedure. Blow out your splint and dispose of it in
the trash can.
CHEMISTRY IN CONTEXT
LAB 8: METALS WITH ACIDS, PAGE 3
CYCLE 5
NAME
6) Now, it is time to note the physical changes of the products (two substances after they
have reacted). Record your observations in the table in the Data/Observations section.
7) Discard the products in the beaker labeled WASTE at the prep. lab bench. DO NOT
dispose of them by pouring them down the drain. You MAY wash out the test tubes at
the sinks after the waste has been dumped. Clean up all materials before proceeding to
Part B.
Part B: Releasing Heat
1) Use the balance at the prep lab bench and a massing pan (also at the main lab bench) to
measure out approximately 2g of iron filings (NOTE: If you are a little over or a little
under 2 grams, NO PROBLEM!) Note the appearance of the iron in the table in the
Data/Observations section.
2) Pour 3mL of hydrochloric acid in an empty test tube. Note the appearance of the
hydrochloric acid in the Data/Observations section.
3) Carefully pour the iron into the test tube with the hydrochloric acid. Swirl the solution a
little. Note the reaction occurring. Touch the bottom of the test tube and note how it
feels. Describe your observations in the table in the Data/Observations section.
4) Discard the products in the beaker labeled WASTE at the prep. lab bench. DO NOT
dispose of them by pouring them down the drain. You MAY wash out the test tube at the
sinks after the waste has been dumped. Clean up all materials before leaving your lab
bench OR taking off your safety wear.
Part C: Cleaning up the Metal
1) Pour 3mL of hydrochloric acid in an empty test tube. Note the appearance of the
hydrochloric acid in the Data/Observations section.
2) Acquire a rusty nail. BE CAREFUL NOT TO POKE YOURSELF! Note the appearance
of the nail in the Data/Observations section.
3) Slide the nail into the test tube with the HCl. Swirl the solution but do NOT allow the
HCl to splash out the top!
4) Allow the reaction to proceed for approximately 5 minutes. Swirl the test tube every
minute. At the end of 5 minutes, note the appearance of the HCl and nail in the
Data/Observations section.
CHEMISTRY IN CONTEXT
LAB 8: METALS WITH ACIDS, PAGE 4
CYCLE 5
NAME
DATA/OBSERVATIONS:
Observations Table:
PART A:
Reactants
Before Reaction
Products
After Reaction
Reactants
Before Reaction
Products
After Reaction
Reactants
Before Reaction
Products
After Reaction
Zn
HCl
PART B:
Fe
(filings)
HCl
PART C:
Fe
(nail)
HCl
CHEMISTRY IN CONTEXT
LAB 8: METALS WITH ACIDS, PAGE 5
CYCLE 5
NAME
ANALYSIS:
1)
In Part A, how did you know if hydrogen was produced by the reaction of the metal
and acid?
2)
In Part B, what evidence did the reaction provide that hydrogen gas was being
produced by the reaction of the metal and acid?
3)
In Part C, what evidence did you have that a reaction was taking place?
4)
Why is He better to use than H in blimps and balloons? (List two reasons.)
a)
b)