Lab 27. stoichiometry and chemical reactions: which balanced chemical equation best represents the thermal decomposition of sodi
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<u>Answer:</u> The final concentration of potassium nitrate is
<u>Explanation:</u>
To calculate the molecular mass of solute, we use the equation used to calculate the molarity of solution:
We are given:
Mass of potassium nitrate (solute) = 0.360 g
Molar mass of potassium nitrate = 101.1 g/mol
Volume of solution = 500.0 mL
Putting values in above equation, we get:
To calculate the molarity of the diluted solution, we use the equation:
.......(1)
- <u>Calculating for first dilution:</u>
are the molarity and volume of the concentrated
solution
are the molarity and volume of diluted
solution
We are given:
Putting values in equation 1, we get:
- <u>Calculating for second dilution:</u>
are the molarity and volume of the concentrated
solution
are the molarity and volume of diluted
solution
We are given:
Putting values in equation 1, we get:
Hence, the final concentration of potassium nitrate is
Answer:
a)
⇒
⇒
b)
⇒
⇒
Explanation:
A)
Remember that positive number superscripts mean electrons lack and negative numbers mean electrons 'excess' (if we compare it with the neutral element). So, for the case of Fe2+ which is converted to Fe3+, we know that in Fe2+ there is a two electrons lack, while in Fe3+ there is a 3 electrons lack; it means that Fe2+ was converted to Fe3+ but releasing one electron:
⇒
The same analysis is applied to Br2; Br2 is a molecule which is said to have a zero superscript because it is an apolar covalent bond; and it is converted to Br-, which, according to what I wrote above, means that there is a one electron excess. So, Br2 must have received an electron in order to change to Br-; but Br2 can't change to Br- as simple as that because Br2 is a molecule, not an atom; it is a molecule that has two Br atoms, so, Br2 must give two Br- ions as products, but receiving one electron for each one:
⇒
b)
Applying the same, in Mg2+ there is a 2 electrons lack, and in Mg is not electron lack (its superscript is zero), so Mg must have released two electrons in order to change to Mg2+:
⇒
Cr3+ has a 3 electrons lack, and Cr2+ a two electrons one, so, Cr3+ must receive an electron to convert to Cr2+:
⇒
We have as a reagent a salt, lead nitrate (Pb(NO3)2), and an unknown solution that gives us as a product lead chloride (PbCl2). That is, the solution must contain chlorine.
If a chlorine solution is used we will have the following reaction:
So, with a chlorine solution, we will have a white precipitate of lead chloride.