Metals & Acids

Thursday, 20 April 2023

Word equations

Reagent + Reagent Product + Product

• Equations are a short hand way of writing the details of chemical reactions.

• The arrow tells us that a reaction has occurred.

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Metal + Acid Metal Salt + Hydrogen gas

Method:1. Add 3 pieces of Mg to 2mL of HCl.2. Collect the gas in a separate upside

down test tube.3. Pass the collected gas over a candle

flame.4. Repeat 1-3 with Zn and Fe.

5. Repeat 1-4 with H2SO4

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Results

• Create a table for your data with the following column headings…..

Reagent 1

Reagent 2

Observations

Collecting H2 gas is best done by holding an empty test tube over the reacting tube. H2 is lighter than air and will collect in the upper tube.

Observations – for each of the metals:

1. What did you see?

2. What did you hear?

3. What did you feel?

4. How do you know the gas was hydrogen?

5. Did the Fe react? How do you know?

6. Describe the speed of the reactions of the three metals?

Complete

Balanced chemical equations

• Balanced chemical equations must have the same number of atoms of each type on the left as the right.

Mg + 2HCl MgCl2 + H2

Left Mg = 1 Right Mg = 1

H = 2 H = 2

Cl = 2 Cl = 2

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Balancing rules…

1. Write the correct formula of all substances in the reaction.

2. Count the numbers of each type of atom on both left and right of arrow.

3. If they are the same….stop, you are done.

4. If they are not the same…add BIG numbers in front to make them balanced.

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How did we get to this point?1. Write the correct formula of all substances

involved…..

Mg + HCl MgCl2 + H2

2. Count the atoms on each side….Left Mg = 1 Right Mg = 1 H = 1 H = 2 Cl = 1 Cl = 23. Add big numbers until the two sides balance.

Mg + 2HCl MgCl2 + H2

1. Then go back and count again to be sure.

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Mg + 2HCl MgCl2 + H2

Left Mg = 1 Right Mg = 1

H = 1 2 H = 2

Cl = 1 2 Cl = 2

• Now it is a balanced equation.

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Other examples…

Zn + HCl

Fe + HCl

Mg + H2SO4

Zn + H2SO4

Fe + H2SO4

Answers

Zn + 2HCl ZnCl2 + H2

Fe(ll) + 2HCl FeCl2 + H2

Mg + H2SO4 MgSO4 + H2

Zn + H2SO4 ZnSO4 + H2

Fe(ll) + H2SO4 FeSO4 + H2

Metals & Oxygen

Thursday, 20 April 2023

Metal + Oxygen Metal Oxide

Method:

1. Hold 1 piece of Mg in tongs over the Bunsen flame.

2. Remove from flame when the Mg begins to spark.

3. Repeat Step 1 with Zn and Fe.

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Metal + Oxygen Metal Oxide

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Equations…

• Write the word equations for these metals:– Magnesium– Aluminium– Zinc

Write balanced chemical equations for each of these metals.

Magnesium + Oxygen Magnesium oxide

22 Mg + O2 22 MgO

Notice that Oxygen always travels in two’s, just like Hydrogen….

O2

H2

Answers…

Zinc + Oxygen Zinc oxide

22 Zn + O2 22 ZnO

Iron (ll) + Oxygen Iron oxide

22 Fe + O2 22 FeO

What would happen if….

• Write the word equation and balanced chemical equation for the following metals if they were reacted with oxygen….

Fe (lll) Cu (ll) Al Ca Na

• When a metal reacts with oxygen it is said to tarnish or corrode if it happens slowly and combust if it happens quickly.

• Rusting is a special term only involving iron or steel and is a type of corrosion.

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RustingIssue HO

Preventing rust

One way of preventing rust is to coat the iron object in tin. This is what has been done to the inside if ‘tin’ cans.

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Sacrificial corrosion

• When two different metals are placed together in an environment in which corrosion can occur, the most reactive metal will corrode before the least reactive.

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• Zinc is used to protect iron from rusting.• Zinc is the more reactive metal and so will

corrode first.• Patches of zinc are placed on the hull of

an iron boat and will react before the iron, even though the iron is exposed to the same environment.

• The iron will start to corrode only AFTER most of the zinc has corroded away.

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• Only 1% of a boats hull needs to be covered in Zn.

18.1kg Zn anode

Metals Metals & &

WaterWater

Thursday, 20 April 2023

Metal + Water Metal + Hydrogen hydroxide

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Results of metals reacting with hot and cold water.

Metal Hot or Cold water?

Pre-weight

(g)

Post-weight (g)

Difference (g)

Mg

Fe

Zn

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Cold

Cold

Hot

Hot

Hot

Cold

Method:1. In a clean test tube place 1 piece of

wet Mg pre-weighed in grams.

2. Add 2mL of tap water.

3. Leave for 2 minutes.

4. Re-weigh in grams.

5. Repeat steps 1-4 for Mg in hot water.

6. Repeat steps 1-5 for each of the following metals: Fe and Zn

Tidy up all the lab gear!!

Conclusion:

Write a conclusion based on the aim and your data.

Questions:

1. Explain why you wet the metal the first time you weighed it?

2. Explain the observedobserved difference in the reaction of the metal with cold and hot water?

EquationsGeneral Word equation:

CopyCopyExample Word equation:

Metal

+Water Metal

hydroxide

+ Hydrogen gas

Iron

+Water Iron

hydroxide

+ Hydrogen gas

Symbol equation:

Fe + 2H2O Fe(OH)2 + H2

Rank the metals you tested from most reactive to least reactive.

Hopefully….

….you saw the following two patterns….

1. Reactivity of metals…Mg>Zn>Fe

2. Hot water was more reactive than cold.

Symbol equations

Each side of the arrow must have the same number of each atom to

be balanced.

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1 x Fe

4 x H

2 x O

Fe + 2H2O Fe(OH)2 + H2

1 x Fe

4 x H

2 x O

What goes into the test tube must be there at the end, just rearranged.

Remember

…BalancedBalanced

Mg + 2H2O Mg(OH)2 + H2

1 x Mg

4 x H

2 x O

1 x Mg

4 x H

2 x O

Have you noticed the BIG 2?

2Al + 6H2O 2Al(OH)3 + 3H2

2 x Al

12 x H

6 x O

2 x Al

12 x H

6 x O

What do you think these numbers mean??

22Al + 66H2O 22Al(OH)3 + 22H2

Reactivity Series

Metals have different reactiveness…

• Very reactive metals react quickly.

• Less reactive metals react slowly.

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Name Symbol Reactivity

Sodium Na Most reactive

Calcium Ca

Magnesium Mg

Aluminium Al

Zinc Zn

Iron Fe

Lead Pb

Copper Cu Least reactive