#4 Acids And Redox Flashcards
What is the uncertainty for a 10 cm³ pipette?
-+0.04 cm³
What is the uncertainty for a 25 cm³ pipette?
-+0.006 cm³
This indicates a higher precision compared to the 10 cm³ pipette.
What is the uncertainty for a 50 cm³ burette?
-+0.10 cm³
To what decimal place is a burette reading recorded?
Two decimal places
A burette reading will either end in 5 or 0.
What is the first step in the acid-base titration
Add a measured volume of one solution to a conical flask using a pipette
What is the second step in the acid-base titration
Add the other solution to a burette and record the initial burette reading to the nearest 0.05 cm³
This allows tracking of the volume used during the titration.
What is the third step of the acid-base titration
Add a few drops of an indicator to the solution to a conical flask
What is the fourth step of the acid-base titration
Run the solution from the burette into the conical flask (while stirring)
Eventually the indicator changes colour at the end point of the titration. (End point is used to indicate the volume of one solution that exactly reacts with the volume and the second solution
What is the fifth step in the acid-base titration
Record the final burette reading
(The volume of solution added from the burette is called the titre)
## Footnote
What is a trial titration used for?
To find the approximate titre
What should be done after the trial titration?
Repeat the titration until two concordant results are found
Concordant results are those that are within 0.10cm3 of each other
When calculating the mean from titration results, what should be used?
Only the concordant results
Fill in the blank: The endpoint indicates the volume of one solution that exactly reacts with the volume of the second solution, known as _______.
the titre
What key information can be determined from the results of a titration?
The concentration (C1) and the reacting volume( V1)of the solutions, and the reacting volume (V2) of the other solution
How to determine an unknown concentration? Step 1
Step 1: mol=conc x vol
Work out the amount (mol) of the solute in the solution for which you know both the C1 (conc of reacting volume) and V1 (reacting vol of other solution)
How to determine an unknown concentration? Step 2
Step 2: Use the ratio of mol in the equation to work out mol of solute of other solution
How to determine an unknown concentration? Step 3
Step 3: Conc= mol/vol
Work out unknown info about solute in other solution
What reaction do you use to identify a carbonate?
Titration
Step 1: prepare solution of unknown carbonate (in volumetric flask)
Step 2: using pipette measure 25.00cm3 of solution (in conical flask
Step 3: using a burette nitrate this solution using 0.100 mol dm-3 HCl
How to identify an unknown carbonate from a titration?
Step 1: calculate the amount of HCl that that reacted. Use the mean titre (v) and the conc of HCl (c 0.100mol do-3)
n(HCl)=c x v/1000
Step 2: determine mol of unknown (ie X2CO3) that reacted using stoichiometry and use equation n(HCl)
Step 3: work out unknown info
-Scale up to find amount of X2CO3 in 250cm3 solution
(Find scaling factor by dividing 250 by the titre)
Mol x scaling factor
- find the molar mass of X2CO3
(Use the amount of n(X2CO3) in the 250cm3 solution and the mass (m) of X2CO3 used to prepare solution)
n(X2CO3)= m/M
M(X2CO3)= m/n= …/… = … gmol-1
Step 4: … gmol-1 - 60.0(Mr CO3) /divide all by 2 = … gmol-1 -> (use periodic table to find the element
What is the oxidation number in pure elements?
Zero
(I.e , H2, O2, P4, Na etc)
What is the oxidation number?
An atom uses electrons to bond with atoms or other elements, the oxidation number is the number of electrons it uses
Oxidation rules:
-oxidation number always 0 for pure elements
-oxidation number for ions is the same at the charge
-compounds add up to 0
-poly atomic ions add up to the charge
What is the oxidation number of an uncombined element?
0
What is the oxidation number of oxygen combined?
-2
What is the oxidation number of hydrogen combined?
+1
What is the oxidation number of an ion of an element?
The charge
What is the oxidation number of fluorine combined?
-1
What are the special case rules of oxidation numbers?
- H in metal hydrides = -1 e.g NaH, CaH2
-O in peroxides = -1 e.g H2O2
-O bonded to F = +2 e.g F2O
