Transcript Mole-Mole Ratios - Blended learning

Mole-Mole
Ratios
Post-Lab Discussion
1. Continuous Variations
 In
the continuous variations method the
ratio of moles of reactants is gradually
changed while a constant solution
volume is maintained. The reaction is
exothermic. The maximum amount of
heat will be given off when the correct
mole ratio is combined. Because the
solution volume is constant, the change in
temperature at the optimum mole ratio
will be the greatest.
2. Total volume kept
constant…
 The
maximum amount of heat is given off
when the optimum mole ratio of
reactants is combined. If the solution
volume is a constant, the change in
temperature will be proportional to the
amount of heat evolved. If the volumes
were not constant, a calculation would
have to be made relating temperature
change to heat evolved for each
measurement.
3. Same concentrations?
 If
the concentrations were not the same,
a calculation must be made for each
measurement to relate the temperature
change to the heat evolved and moles
reactants present.
 Having the same concentrations
eliminates the need for this extra
calculation.
4. Limiting Reagent?
 The
limiting reagent is the reagent that is
completely consumed in a chemical
reaction.
5. Limits the precision?
 The
volume reading limits the precision.
This measurement relies on the human
eye to measure EXACT amounts with a
graduated cylinder. The temperature
reading was given out with decimal
places.
6. Limiting Reagent upward?
 On
the upward sloping line of the graph,
the limiting reagent is the Hypochlorite ion
and the excess reagent is the thiosulfate
ion, until the 40 mL mark.
6. Downward sloping line?
 Thiosulfate
ion is the limiting reagent and
the excess reagent is the hypochlorite.
 The
perfect ratio: Where there is no
limiting or excess reagent?

Where the lines intersect: 40 mL
hypochlorite to 10 mL thiosulfate.
7. Physical Properties?
 Some
other properties which could be
used are the intensity of the color of a
reactant or product, the mass of a
precipitate that forms, or the volume of a
gas that forms.
8. Why graph?
 In
may be that the exact mole ratio was
not chosen as a data value. Also, the
graph averages several values to find the
optimum ratio rather than relying on only
one value.
9. If the two solutions are not at
the same initial temperature, a
correction must be made to find
the correct change. How?
 Graph
the Delta Temp vs. Volume if temp
is not the same of two solutions.
 Graphing the Final Temp vs. Volume is
sufficient if the two solutions are at the
same temp.
61.
Aluminum sulfide reacts with water to
form aluminum hydroxide and hydrogen
sulfide.


A.
balanced equation?
B. how many grams of aluminum hydroxide from 6.75 g of aluminum
sulfide?
67.Define the terms:



Limiting Reagent: - determines the amount of
product formed. It runs out first.
Excess Reagent: -is left over when the
reaction stops.
Why are the amounts of products formed in a
reaction determined only by the amount of
the limiting reactant?

The L.R. is completely used up. No more product
can be made when one of the reactants is
gone.
68. Define the following terms:
 A.
Theoretical Yield: the quantity of
product that is calculated to form when
all of the limiting reactant reacts.
 Actual Yield – the amount of product
actually obtained in a reaction.
 Percent Yield: relates the actual yield to
the theor. Yield.
 % Yield = actual/theor x 100%
73. Given 1 gram of both reactants,
Find the L.R. and grams of CO2 formed,
excess remain

3NaHCO3 + H3C6H5O7  3CO2 + 3 H2O + Na3C6H5O7