SUMMER INSTITUTE – Module 7 – Stoichiometry 2
______________________________________________________________________________________________________________________________________ Module 6 ➙ 8 Jump to: Activity 1, Activity 2, Activity 3, Activity 4, Activity 5, Activity 6, Activity 7, Module Test
Module 7 – Stoichiometry 2 –
5 hours – due August 13th!
* Connections –
The question is how do we get percent by mass data. Do not forget that a percent is a part / whole x 100.
Activity 1: SKILL : Nomenclature of salts
Notice this is another example of a regular repeating crystal of ions like the example for NaCl above EXCEPT that the +1 will be from a the singular ion (fuscia = Na+) and the negative ion will result from a group of atoms bonded (polyatomic ion) called a nitrate ion
(NO3 -1 = 1 nitrogen and 3 oxygens bonded). Notice that 1 positive ion = 1 negative ion.
Both NaCl and NaNO3 are examples of SALTS which are crystals of ions at room temperature.
Notice that these are clusters of atoms that have their own name:
For example in NaCl we call that
sodium chloride – (IDE if just single atom)
If we have NaNO3 we call that
sodium nitrate – (nitrate is the name of NO3-1)
Notice that Na is the formula is really Na+1
What about CuSO4 ?
What must be the charge of Cu (copper) if the formula is written this way?
Al likes to become +3: (by losing 3 electrons)
This charge tells us that Al likes to become Al+3 when it reacts (loses 3 electrons)
Cl likes to become -1: (by gaining an electron)
The ions involved: Al+3 and Cl-1 thus we need 1 Al+3 per 3 Cl–
We write this this way: AlCl3 (subscript 3 means 3 Cl ions)
Notice that 1 Aluminum ion (+3) and 3 Chloride ions (-1 each) must equal zero.
How do we handle multiple charges that the positive ion can have?
For instance copper because it can be +1, and +2 it can make 2 compounds with the nitrate ion and so can nickel. Some metals can become more than one charge.
It can be CuNO3 when Cu is +1 and it can beCu(NO3)2 when Cu is +2
Since they have different chemical formulas they will have different properties and thus need 2 different names. They both cannot be copper nitrate is there are 2 versions?
The way to get round this is to use something called the stock system:
Thus CuNO3 is copper (I) nitrate and Cu(NO3)2 is copper (II) nitrate.
THE ROMAN NUMERAL IS THE EXACT CHARGE OF THE 1st ELEMENT!
Why didn’t we call Al(NO3)3 aluminum (III) Nitrate?
What is the name of Ni2O3? Answer at the bottom of activity 1
Table S (element name and symbols) and Table E (what the heck is that!) are your friends here!
3 : Lecture 3.0 – Naming and Writing Formulas for Binary Salts
3 : Lecture 3.1 – Naming and Writing Formulas for Ternary (polyatomic) Salts
Activity 2: SKILL : Percent Water in a Hydrate.
| This image was build by X-ray imaging of salt.
Now it is more complex than the crystal above for NaCl because we have a polyatomic ion in the crystal.
The Yellow is the sulfur attached to 4 oxygens (red). The brown color (i think its brown) is the copper ion.
Notice regular repeating pattern.
If you look carefully inside the crystal there is one Cu per sulfate ion.
|CuSO4 · 5 H2O||Notice the Dot between anhydrate and water. This dot means “WITH” and not to multiple. Thus there are exactly 5 water molecules for every 1 Cu+2 and 1 SO4-2 in the crystal.|
You will notice that water (it has 2 white hydrogen atoms) molecules are situated inside the crystals at particular regions in the crystal in exact ratios. Stiochiometric ratios
It is hard but you can see the 5 water molecules per 1 copper ion and 1 sulfate ion.
What makes it hard is that the crystal repeats in all directions.
The water can be removed from the salt by heating it.
Activity 3: SKILL: Hydrate assessments:
Activity 4: SKILL: Conservation of Mass – Stoichiometry of Chemical reactions an identifying reactions.
hydrate → anhydrate + water
2 : The Diehl Lectures 3 – Balancing and Reaction Identification
*Remember that we originally obtained the chemical formula for water BEFORE the mole concept? We used gases and their property that the same volume = same number of particles (Avogadro’s hypothesis) to obtain the formulas AND THEIR RATIOS!!
Pringles Can Demo:
A Pringles Can is filled with hydrogen gas, H2 by a tube that carries the very light gas (lighter than air) from the reaction vessel. There is a hole on top of the can (that is upside down) and a hole on the bottom of the can. I filled the can with hydrogen from the bottom and it filled the can upward because it is lighter than air. The hydrogen flushed out the atmospheric air out of the container leaving only pure hydrogen. I disconnected the lower tube and lit the pure hydrogen on the top. As the pure hydrogen burns Air with oxygen is pulled into the can from the bottom hole and an explosion only occurs when the ratio of hydrogen to oxygen reached 2 : 1. Thus there is a delay when the hydrogen is lit UNTIL the correct ratios are reached. We get these ratios (or ingredients) when we balance a chemical equation!
Hydrogen Balloon Explosions Demo:
I fill 2 balloons. One with 100% hydrogen and one with 66.6% Hydrogen and 33.3% (2:1 Ratio) and compare the explosions. Remember from reaction of hydrogen and oxygen above, that Energy is given off exothermically in the reaction. If more energy is given off then the reaction is more efficient due to the correct ratio of particles that is needed to react is present. When ratios are not ideal then reactions are slower and sometimes do not react at all with a lot of waste.
Activity 5: SKILL: Identifying reactions and Balancing Reactions
Balancing and identifying reactions Key 2014.pdf
Balancing Chemical Reaction Concoction 2015 KEY.pdf
Activity 6: SKILL: Use Mole ratios of chemicals in a chemical reaction to predict the quantity of another chemical in the balanced chemical reaction.
Module Test 7 – Reaction Identification/ balancing /Stoichiometry/ Assessment –
– available below