Chemistry Lab Flashcards
What is a hydrate?
a hydrated compound that has a specific number of water molecules associated with in as part of the CRYSTAL STRUCTURE
What is oxalate?
C2O4
What is oxalic acid?
H2C2O4*2H2O - oxalate bonded to 2 water molecules with hydrogen bonding
What is copper sulphate pentahydrate? How are the water molecules bonded?
CuSO4*5H2O - blue solid - 5 H2O molecules COORDINATED to the Cu and SO4 coordinated to sulphate
What is anhydrous copper sulphate?
CuSO4 - no water molecules - white solid
What could happen when hydrated solids are heated?
- decompose
or
- some or all water molecules removed
What are the conditions necessary to calculate the mass percent of water removed from a hydrated solid?
water molecules removed without decomposition and solid is at a constant mass
What is density dependant on for solid and liquids? Gases?
Solids and liquids – temperature
gases – temperature and pressure
How is density measured for solids & liquids? Gases?
solids and liquids – g/mL
gases – g/L
What is the formula for density?
D=m/V (mass/volume)
How do you calculate the mass of water removed?
initial mass of sample - final mass of sample
How do you calculate the % of water removed from a hydrated salt?
mass of water removed/initial mass of sample x 100
Why is it important to have a sample that was heated return to room temperature?
heat creates air currents that destabilize the balance pan = inaccurate mass measurement
Which type of weighing scale is more accurate?
analytic balance (compared to top loading)
What observations are seen when the hydrated salt is heated?
condensation on the inside of the glass; water vapour shown as bubbles
What is Potassium Trioxalatoferrate (III) trihydrate?
K3[Fe(C2O4)3)]*3H2O - coordination compound
What are the components of a coordination complex?
central METAL atom/ion bonded to two or more LIGANDS
What is a coordination compound?
A NEUTRAL substance that contains a coordination complex
What is the difference between a coordination compound and coordination complex?
compound - CATIONIC, ANIONIC, NEUTRAL
complex - contains compound and NEUTRAL
What is the coordination complex in (NH4)2[Fe(H2O)6(SO4)2?
[Fe(H2O)6]^2+
–> cationic
How are the water molecules bonded in the [Fe(H2O)6]^2+ complex? What does that mean for reactions?
H2O weakly bonded to Fe with hydrogen bonds that can be REPLACED by stronger bonding groups LIKE OXALATE ION
What is Iron (II) oxalate dihydrate?
Fe(C2O4)*2H2O - water molecules attached to Fe and oxalate ions bridge two water molecules (low solubility)
What is the purpose of of oxalic acid when reacting with ferrous ammonium sulphate hexahydrate?
oxalate ions will replace water molecules to produce iron (II) oxalate dihydrate (yellow insoluble compound)
After oxalic acid and ferrous ammonium sulphate hexahydrate have reacted what are the products?
iron (II) oxalate dihydrate
water molecules
ammonium hydrogen sulphate
Why must the solution be decanted?
remove excess liquid (composing of ammonium hydrogen sulphate and mainly water)
more water = larger solution volume = lower yield
What excess reagents are added to Ion oxalate dihydrate (Fe(C2O4)*2H2O) to produce Potassium trioxalatoferrate (III) trihydrate?
excess hydrogen peroxide -H2O2 - (oxidize)
excess potassium orate monohydrate
excess oxalic acid dihydrate
Once the reagents are added what is done to the solution? why? What is the issue with the product)
heated to remove excess reagent (but potassium trioxalatoferrate (III) trihydrate is still soluble in water)
What is added and done to the potassium trioxalatoferrate trihydrate to remove water?
ethanol added to help precipitate and filter the product. Buchner filter is used.
solution is also placed in an ice bath because solubility is low in cold temperatures
What is the limiting reagent?
substances that runs out first (determines maximum amount of product that could be made - theoretical yield)
What is the percent yield?
actual yield/theoretical yield x 100
What is quantitative analysis?
determining the AMOUNT of a specific component in some sample
What is GRAVIMETRIC analysis?
- type of quantitative analysis
- finding the change in mass associated with a chemical or physical process (ex. mass % of water removed from hydrated salt)
What is a VOLUMETRIC ANALYSIS?
- type of quantitative analysis
- measuring the VOLUME of a SOLUTION required to react completely with another substance (ex. titration)
What is the TITRATION process?
- type of volumetric analysis
- a STANDARD SOLUTION (of accurately known concentration) is gradually added to a known AMOUNT of ANALYTE (unknown solution) until all the analyze has reacted (EQUIVALENCE POINT)
Why is an indicator necessary in a titration?
provides colour change once the endpoint of the reaction is reached due to concentration changes
What is lithification?
imprints of shells that were compacted to make stone
What occurs to carbonate compounds under acidic conditions?
production of CO2
CaCO3 + H2SO4 –> CaSO4 + CO2 + H2O
–> limestone dissolves
What is HARDNESS? What is used for its calculations?
amount of Ca and Mg dissolved in water in ppm
–> all calcium and magnesium species are treated as calcium carbonate
How can you calculate the harness in ppm?
mass of solute (mg)/mass of solution (kg)
or mass of solute (g)/mass of solution (g) x10^6
How can you calculate hardness for CaCO3 in water?
mass of CaCO3 in mg/volume of water in L
How do ligands act as Lewis bases?
react with metal cations (Lewis acids) to donate electron pairs
What is a monodentate ligand? What is a chelating ligand? How do they compare in bond strength?
monodentate ligand - has ONE ATOM that donates the electron pair
chelating ligand - has TWO or MORE ATOMS that donate the electron pair
chelating ligands bond to metal ions TIGHTLY and can easily DISPLACE monodentate ligands
What is Calmagite?
indicator that is a bidentate ligand ( O and O) forming a coordination complex with Mg2+
–> creates red coloured complex when its bond with Mg2+ is displaced by EDTA
What is acid digestion?
carbonate salts reacting with acids to release CO2
What are the insoluble materials when reading dolomitic limestone and oyster shells with acids?
insoluble non-carbonate materials (carbonate materials ARE soluble)
What is the carbonate material in dolomitic limestone?
dolomite: CaMg(CO3)2
What is the carbonate material in oyster shells?
CaCO3
Why is there a change in mass in acid digestion?
loss of CO2 gas – now can determine the mass percent of CARBONATE SALT in the sample (limestone and oyster shell)
What is the dolomitic limestone reaction with acid?
MgCO3 + CaCO3 + 4HCl –> CaCl2 + MgCl2 + 2CO2 + 2H2O
- magnesium and calcium carbonate with hydrochloric acid produces soluble salts calcium and magnum chloride and CO2
What is the oyster shell reaction with acid?
CaCO3 + 2HCl –> CaCl2 +CO2 + H2O
- calcium carbonate with hydrochloric acid
Why are the oyster shells and limestones crushed?
increases surface area = increases reaction rate
Why is potassium borate buffer added to each titration flask?
maintain pH near 10 for EDTA and Calmagite indicator to bond to metal ions
What does the reaction look like when indicator is added at the start with the sample?
Ca2+ + Mg2+ +In3- –> Ca2+ + MgIn- (red)
–> indicator bonds with Mg more strongly producing a red colour
What does the reaction look like when EDTA is added initially?
Ca2+ MgIn- (red) + EDTA4- –> Ca[EDTA)]2- + MgIn-
–> EDTA first starts bonding with Ca more strongly
What happens when more EDTA is added?
Indicator is displaced and EDTA bonds with Mg
Then hydrolysis reaction occurs between displaced Indicator and H2O: which produces the blue endpoint colour:
In3- (colourless) + H2O –> HIn2+ (BLUE) + OH-
What is the identification of a gas test? Example?
heating a solution to identify the species present
–> reaction between NH4+ (ammonium ion) and sodium hydroxide (NaOH) produces gaseous ammonium (NH3) when heated – weak base causes red litmus paper to turn blue
What is the flame test?
ALL elements emit light of a characteristic COLOUR when heated
- heat energy excites an electron in an atom to a higher energy level
- electron returns to a lower energy level and this energy is given off as light
- since different elements have unique energy levels different elements produce different colours of light
- element can be identified id the frequency of light is in the visible spectrum
What is a precipitation reaction?
two AQUEOUS species react and an INSOLUBLE product is formed
How can precipitate be observed?
crystals or cloudy due to solid
– colour is important (ex. silver chloride is white but silver bromide is beige) - transition metals are strongly coloured
What is a solution?
homogenous mixture (all species are in the same phase or state) with no precipitate
What is a heterogeneous mixture?
two phases present (ex. precipitate in liquid)
What is suspension? What is a colloid?
suspension - precipitate that eventually settles
colloid - precipitate do not settle
What does the flame experiment test for? What are the results?
butane torch used and observe initial colour
- Sodium – bright orange-yellow light
- Lithium – red-maroon light
- Potassium – pale purple light
What does the sodium hydroxide and aqueous ammonia solution test for?
Transition metals-first add NaOH to create metal+hydroxide then add NH3
Copper (II) - blue solution
Zinc 2+ - colourless solution
Aluminum 3+ - insoluble white solid + no ammonium reaction
Iron II - insoluble green solid
Iron III - brown solid
How was the Bromide and Iodide Ions tested for?
chloride water added to Br and paraffin oil is added so upper layer colour is orange
chlorine water addd to I- and paraffin oil is added so upper layer is purple
How is the Sulphate Ion tested for?
unknown + barium which is INSOLUBLE in an acidic solution, so HCl is added
How is the Carbonate Ion tested for?
unknown solution + HCl creates CO2 seen as small bubbles
How is Chloride and Fluoride tested for?
unknown + AgNO3 –> AgCl creates a white solid (chloride test)
unknown + Ag –> no reaction (fluoride test)
How is phosphate ion tested for?
phosphate ion forms a yellow precipitate with ammonium molybdate
