Redox Reactions
What is a oxidation reduction (redox) reaction?
A reaction in which the transfer of electrons occurs (one element/molecule loses and one gains)
The oxidation number of any uncombined element (free element state) is always________
0
When red litmus paper is dipped into a solution it turns blue. This means the substance is a _____
base
The burette and pipette are commonly used in which chemistry experiment
acid base titrations
What type of ions migrate to the anode and cathode of an electrolytic cell
positive ions move to the anode
negative ions move to the cathode
Define oxidation in terms of electron transfer.
oxidation=lost of electrons
The oxidation of oxygen ion is always ________ except in a peroxide where it is _____
-2 and -1
Blue litmus paper when dipped into a substance turned red but red litmus paper when dipped into the same substance did not change. This means the substance is a _____
acid
After three trials the following volume of acid used was observed
Trial 1 - 25.03 Trial 2 - 26.23 Trail 3 - 25.10
Calculate the average volume of acid used
(25.03 + 25.10)/ 2 = 25.07cm3
What is an active electrode
An active electrode actively participates (ionizes) in the chemical reaction
Define reduction in terms of electron transfer.
reduction=gain of electrons
The oxidation number of hydrogen is always___________ unless it is in a metal hydride its oxidation number becomes
+1, -1
When a metal such as Magnesium reacts with an acid such as H2SO4 what are the products formed
A salt MgSO4 and Hydrogen gas H2
Calculate the number of moles of HCl used if it's concentration is 0.55 moldm-3 and its volume is 25.07cm3
0.55 x 0.02507 = 0.0138 moles
Write a half equation for what happens at the anode in a solution of concentrated sodium bromide
2Br-(aq) --> Br2(aq) + 2e-
Which group of elements loses electrons easily to form positive ions?
metals
The oxidation number of Mn in K2MnO4 is
+6
Carbonates and bicarbonates react with acids to form?
In the equation 2NaOH + H2SO4 --> Na2SO4 + 2H2O
The mole ratio of base to acid is
2 mol of base :1 mole of acid
Cu2+(aq) + 2e- --> Cu(s)
Name 2 "real world" examples or uses of redox reactions.
rusting, bleaching stains in fabrics, decomposition of hydrogen peroxide
List the oxidation numbers for all of the following elements/molecules and tell what is reduced and what is oxidized. 2 AgCl(s) + H2(g) → 2 H+(aq) + 2 Ag(s) + 2 Cl-
+1 -1 0 +1 0 -1 reduced-Ag oxidized-H
Write the balanced chemical equation for the reaction of potassium carbonate KHCO3 with HCl
KHCO3 + HCl --> KCl + H2O + CO2
Calculate the mass sodium in a sodium sample. Given that the number of moles of sodium is 0.05mol and the molar mass of Na is 23 g mol-1
1.15g
During the electrolysis of concentrated sodium chloride what change is observed in the electrolyte as chlorine is lost at the anode and hydrogen is lost at the cathode
The electrolyte becomes more alkaline (basic) as NaOH is formed