Metals & Acids Wednesday, 28 October 2015

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. Copy

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 H 2 SO 4 Copy this word equation

Results Create a table for your data with the following column headings….. Reagent 1 Reagent 2 Observations

Collecting H 2 gas is best done by holding an empty test tube over the reacting tube. H 2 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 MgCl 2 + H 2 Left Mg = 1Right Mg = 1 H = 2 H = 2 Cl = 2 Cl = 2 Copy

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. Copy

How did we get to this point? 1.Write the correct formula of all substances involved….. Mg + HCl MgCl 2 + H 2 2.Count the atoms on each side…. Left Mg = 1Right Mg = 1 H = 1 H = 2 Cl = 1 Cl = 2 3.Add big numbers until the two sides balance. Mg + 2HCl MgCl 2 + H 2 4.Then go back and count again to be sure. Copy

Mg + 2HCl MgCl 2 + H 2 Left Mg = 1Right Mg = 1 H = 1 2 H = 2 Cl = 1 2 Cl = 2 Now it is a balanced equation. Copy

Other examples… Zn + HCl Fe + HCl Mg + H 2 SO 4 Zn + H 2 SO 4 Fe + H 2 SO 4

Answers Zn + 2HCl ZnCl 2 + H 2 Fe(ll) + 2HCl FeCl 2 + H 2 Mg + H 2 SO 4 MgSO 4 + H 2 Zn + H 2 SO 4 ZnSO 4 + H 2 Fe(ll) + H 2 SO 4 FeSO 4 + H 2

Metals & Oxygen Wednesday, 28 October 2015

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. Copy this word equation

Metal + Oxygen Metal Oxide Copy this word equation

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 2 Mg + O 2 2 MgO Notice that Oxygen always travels in two’s, just like Hydrogen…. O 2 H 2 Answers…

Zinc + Oxygen Zinc oxide 22 2 Zn + O 2 2 ZnO Iron (ll) + Oxygen Iron oxide Fe + O 2 2 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)AlCaNa

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. Copy

Rusting Issue 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. Copy

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. Copy

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. Copy

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

18.1kg Zn anode

Metals & Water Wednesday, 28 October 2015

Metal + Water Metal + Hydrogen hydroxide Copy this word equation

Results of metals reacting with hot and cold water. MetalHot or Cold water? Pre- weight (g) Post- weight (g) Difference (g) Mg Fe Zn Copy Cold 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? observed 2.Explain the observed difference in the reaction of the metal with cold and hot water?

Equations General Word equation: Copy Example Word equation: Metal + WaterMetal hydroxide + Hydrogen gas Iron + WaterIron hydroxide + Hydrogen gas Symbol equation: Fe + 2H 2 O Fe(OH) 2 + H 2

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. Copy

1 x Fe 4 x H 2 x O Fe + 2H 2 O Fe(OH) 2 + H 2 1 x Fe 4 x H 2 x O What goes into the test tube must be there at the end, just rearranged. Remember… Balanced

Mg + 2H 2 O Mg(OH) 2 + H 2 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 + 6H 2 O 2Al(OH) 3 + 3H 2 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?? Al + 6H 2 O 2Al(OH) 3 + 2H 2

Reactivity Series Metals have different reactiveness… Very reactive metals react quickly. Less reactive metals react slowly. Copy

NameSymbolReactivity SodiumNaMost reactive CalciumCa MagnesiumMg AluminiumAl ZincZn IronFe LeadPb CopperCuLeast reactive