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stoic Flashcards

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1
Q

hygroscopic

A

readily absorb water

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2
Q

what features must a primary standard have?

A

solid, hygroscopic, highly soluble, cheap, stable, pure

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3
Q

aliquot

A

specific volume of a solution (measured using a very accurate piece of glassware

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4
Q

titre

A

stuff we add to aliquot- measured in the experiment

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5
Q

compare graphs of ph v.s. volume of base/acid

A

inverse relationship between volume of base added and volume of acid added

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6
Q

equivalence point

A

one to one ratio of acid and base

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7
Q

why do we have to make sure glassware is not contaminated

A

might change concentration of solution

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8
Q

why doesn’t it matter when we add base into container of deionised water?

A

number of moles of the base doesn’t change (can get diluted in the pipette though

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9
Q

Atomic mass of an element is…

A

the weighted average of the masses of its isotopes.

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10
Q

The mole is…

A

The number of atoms present in 12.0 grams of carbon-12

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11
Q

Molar mass is equal to…

A

mass in grams of one mole of the substance

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12
Q

Homogenous

A

you cannot see the particles of solute dissolved in the solvent

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13
Q

Why do we need to create solutions?

A

Chemical reactions between 2 solids are very rare, because there is very little contact between the two (surface area is smaller)

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14
Q

How does “strong acid” describe?

A

much dissociation occurs.

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15
Q

How do you calculate the parts per million (PPM) of a solution?

A

EITHER
1. Find molarity (concentration in mol/L)
2. Multiply it by the molecular mass
3. Multiply results by 1000 (turn g/L to mg/L)
OR
1. Assume there is 1L of solution, so the concentration given (e.g. c= 0.0020 mol/L) becomes 0.0020 mols (n) and 1 litre of solution (1000 g)
2. use the number of moles and the molar mass of the solute to find its mass.
3. Use the formula
“concentration (ppm)= (mass of solute/ mass of solution)* 10^6”

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16
Q

What’s the difference between the measurements of molarity and parts per million?

A

Molarity: number of moles per unit volume
PPM: measure of proportion by mass

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17
Q

How can we determine when we can convert the calculation to the PPM measurement and when we can’t?

A
  • can use when solution is diulte enough that adding the solute does not appreciably change the solution’s volume or mass
  • if get over 1000 ppm, then ppm is not the right unit
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18
Q

Percentage mass/ volume

A

expresses concentration as a mass of solute in grams per 100 mL of solution.

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19
Q

Percentage mass/ volume formula

A

concentration (%) m/v= (mass of solute (g)/ volume of solution (mL)) *100

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20
Q

What is another way, other then ppm, mass/volume, and molarity, to express the concentration of liquid solutes?

A

percentage by volume

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21
Q

Percentage by volume formula

A

concentration (%) v/v= volume of solute (mL)/ volume of solution (mL) *100

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22
Q

In what circumstances is the percentage by volume presentation of concentration used most often?

A

In alcohol beverages.

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23
Q

Percentage composition by mass formula

A

% of x in a compound= molar mass of x in compound/ molar mass of compound *100

24
Q

What is the percentage composition?

A

The relative proportion of the mass of each element in the compound.

25
Q

How do you find the empirical formula for a compound?

A
  1. assume there is 100g of the sample and write the masses of each element (it’s ok to assume because we’re only looking for the simple ratio
  2. calculate the number of moles of each element in 100g of sample
  3. divide each number in the ratio by the smallest number
  4. round off and finish
26
Q

How do you find the molecular formula of a compound?

A
  1. find the empirical formula
  2. sub in the molar masses of each element to then find the overall molar mass
  3. divide the given molar mass of the compound by the calculate one (the empirical formula one)
  4. times it by whatever factor resulted
27
Q

no water in compound

A

anhydrous

28
Q

when the ionic lattice contains water…

A

it’s hydrated

29
Q

How to find the amount of water in a hydrated compound? (the number before H2O)

A
  1. Assume 100g of substance
  2. Turn the percentage by mass of anhydrous compound into grams
  3. Find molar mass of compound, then calculate its number of moles
  4. We can determine the mass of water from the remainder of the percentage
  5. Find molar mass of water, then calculate its number of moles
  6. Compare the 2 using mole ratios (divide the n(h2o) by n(compound), then amount of water can be found
30
Q

Limiting reagent

A

A reagent that is present in an amount stoichiometrically (proportionally) less than the other reagents.

31
Q

What is the role of the limiting reagent in a reaction?

A

Determines the amount of products that is formed, therefore it is important to determine which one is the limiting reagent.

32
Q

How to determine which substance will be limiting in a reaction?

A
  1. Calculate n of both substances
  2. Compare- the one that has a lower number of moles is the limiting one
    *if there is not a 1:1 ratio, divide them by the balancing ratio(the number before the molecule) in the question so there is one
33
Q

Why are we putting excess amounts of reagents in?

A
  • equilibrium considerations
  • ability to collect products as pure substances
  • financial considerations (some are very expensive so they will be used as limiting reagents
34
Q

How can we use the number of moles of a reactant to find the mass of the product?

A
  1. Figure out the number of moles of product using mole ratios (divide by the one you know, multiply by the one you don’t know)
  2. find its molar mass
  3. algebraa
35
Q

How do you show that somehting is in excess in a reaction?

A
  1. figure out number of moles in both reactants
  2. divide them by their balancing ratio
  3. the one that is fatter (the number) is in excess
36
Q

What is the acronym for solubility?

A

SNAPE
Sodium
Nitrate
Ammonium
Phosphate
Ethanoate
THESE ARE ALL SOLUBLE (if they’re there, it’s soluble)

37
Q

Why do I need to find out which reactant is the limiting one before I calculate the mass of the precipitate formed?

A

Because that is the most amount of reactant we can use to produce the maximum amount of precipitate (if we used the excess one the answer will be wrong cuz the other compound will not be enough)

38
Q

How do I find the mass of the precipitate formed considering there is a limiting reagent?

A
  1. write out balanced formula
  2. find number of moles for both reactants
  3. determine the limiting reagent
  4. find n of precipitate with ratios
  5. find mass
39
Q

q: what is the maximum mass of (a product) that can be obtained?

A
  1. find limiting reactant
  2. use the number of moles of that to find number of moles of the product
  3. find mass
40
Q

How to find the mass of the reagent in excess that is leftover after the reaction is complete?

A
  1. use n(moles) of limiting reactant to find n(moles) of the reagent in excess if correct stoichiometry was used (in a scenario with no excess)
  2. use the total n(moles) of excessive reagent to subtract n(moles) of that reagent if it was not excessive
  3. use that n(moles) to find mass
41
Q

Percentage purity formula

A

mass of chemical/ mass of sample *100

42
Q

Gravimetric analysis

A

Any analytical method used for the quantitative determination of an analyte based on its mass.
- by selective precipitation of the substance from an aqueous solution

43
Q

List the steps of finding percentage purity when a dilution occurred beforehand.

A
  1. Figure out n of another reactant
  2. Use mol ratio to find n of target substance in aliquot
  3. Multiply by factor of dilution
  4. Use n and molar mass to find mass
  5. Put into %purity formula
44
Q

List the steps of finding the concentration of a particular ion in the resulting solution.

A
  1. Find its total number of moles (may need to do separate calculations of reactants)
  2. Find volume
  3. calculate
45
Q

Sodium sulfate question (photos)

A

(photos)

46
Q

Coll 2022 pp
75.0 mL of a solution containing 0.293 g of sodium chloride is added to 125.0 mL
of a solution containing 0.555 g of Iron(III) chloride to produce 200.0 mL of mixed solution.
Determine the concentration of chloride ions in the solution.

A

0.0763 M

47
Q

Coll 2022 pp q3b

Lauren, a chemistry student was investigating the concentration of sulfuric acid, ,
in the electrolyte of various car batteries.
To do this she pipetted out 20.00 mL of the electrolyte from one of the cells and
diluted it to 250mL in a standard volumetric flask.

     She placed the diluted acid in a burette and titrated it with 20.00 mL samples 
     of 0.290 mol   sodium hydroxide solution.  

     On average she used 17.35 mL of the diluted solution for the end point.

The equation for the reaction is 2NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l)

(b) Calculate the concentration of the diluted sulfuric acid in the volumetric flask. (2 marks)

A

0.167M

48
Q

2022 pp
Silicon carbide, SiC, commonly known as carborundum is the very hard, black substance
used on many abrasive papers.

     It can be made by heating a mixture of quartz,   and carbon, C, to a high temperature. SiO2(s)+2C(s) --> SiC(s)+ CO2(g) n(SIO2)=16.642 MOL n(C)= 83.264 m(SiC(s))=nm =667g

(b) What mass of the excess reagent would be left over in the above reaction? (2 marks)

A

600g

49
Q

Lauren inadvertently leaves distilled water in the analytical pipette that was used to transfer the sodium hydroxide into the conical flask. What will happen to the calculated value of the sulfuric acid in the car battery electrolyte? Will it be overestimated or underestimated? (2 marks)

A
  • Overestimated
    If the analytical pipette was not rinsed property and excess water remained in the pipette, a lower number of moles of sodium hydroxide will inadvertently be delivered to the conical flask. This will mean a lower titration figure is required from the burette. This will give a false impression that the acid in the burette is more concentrated.
50
Q

Aluminium chloride is formed via the following reaction:
2Al(s)+ 3Cl2(g) –> 2AlCl3(s)
34.0g of aluminium is reacted with 39.0 g of chlorine gas.
c) calculate what mass of the excess reagent is leftover.

A

24.1g

51
Q

How many mole of oxygen atoms are there in 10.0 mole of Ba(OH)2. 8H2O crystals?

A

100 mols

52
Q

4Cr+ 3O2-> 2Cr2O3
If 0.175 mole of chromium is mixed with 0.120 mole of oxygen,
I) which is the limiting reagent?
ii) how many mole of excess reactant remains?

A

O2 is limiting
0.015mol of Cr is excess

53
Q

Acid+metal=
Acid+base=
Acid+carbonate=

A

h2 salt
h2o salt
co2 h2o salt

54
Q

Solutions of sulfuric acid and sodium hydroxide react according to the following equation:
H2SO4(aq)+ 2NaOH(aq) -> Na2SO4(aq)+ 2H2O(l)

25 mL of 1.0 M sodium hydroxide would be neutralized by:
a) 25 mL of 0.50 M sulfuric acid
b) 25 mL of 1.0 M sulfuric acid
c) 12.5 mL of 0.50 M sulfuric acid
d) 50 mL of 1.0 M sulfuric acid

A

A

55
Q

A student is required to produce a 1.50 M standard solution of Na2CO3 for use in a titration. A 40.0g sample of the solid is available and they are required to use as much of the sample as possible. The student has access to four volumetric flasks: 100ml, 200 ml, 250 ml, 500 ml

select the most appropriate sized flask to prepare and justify the choice with calculations (2 marks)

A

Max size possible is 250 mL, any smaller would use insufficient solid, larger leads to dilution.

56
Q

what is the limits for a titre volume to be concordant?

A

less than 0.1 mL difference between largest and smallest

57
Q

describe how to prepare a diluted solution.

A
  1. add a small amount of deionised water to the flask to rinse
  2. pipette solution in
  3. add deionized water to mark
  4. mix

chemistry 3 (3 decks)

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