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Chemistry > 5.1 Moles II > Flashcards

5.1 Moles II Flashcards

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1
Q

1dm3 in cm3?

A

1dm3 = 1000cm3

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2
Q

How do you calculate a mole of gas from its volume alone?

A

Moles = volume (dm3)/ 24dm3

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3
Q

The denominator is….. for every gas

A

24dm3

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4
Q

Calculate the amount in moles in 6 dm3 of CO2?

A

Moles = volume/ 24dm3
= 6/24= 0.25mol

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5
Q

Calculate the amount in moles in 1500cm3 of H2?

A

Moles = vol/24dm3
1500/1000= 1.5
1.5/24= 0.0625 mol

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6
Q

Calculate the volume of 0.8 moles of CH4

A

Vol= moles x 24dm3
= 0.8 x 24
= 19.2dm3

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7
Q

Calculate the volume of O2 needed to react with 10 g of N2

A

N2+2O2→2NO2
1. Convert mass of N2 into moles of N2.
2. Use the mole ratio from the balancing numbers in the equation.
3. Convert moles of O2 into volume of O2

                        1N2   :  2O2 mole ratio:              1   :   2 actual moles:  0.357.. : 0.714... ----> moles N2= 10/28  -----> volume O2= 0.174x24= 17.1dm3 ​  .
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8
Q

What is the shortcut when calculating gas moles from gas moles?

A

-When calculating between gas volumes, you can skip converting to and from moles.
-The 24 dm³ factor cancels out, so you can directly use the mole ratio between gases.

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9
Q

Calculate the volume of NO2 produced from 5 dm3 of N2

A

N2 + 2O2 → 2NO2
1. NO NEED TO Convert volume of N2 into moles of N2.
2. Use the mole ratio from the balancing numbers in the equation.
3. NO NEED TO Convert moles of NO2 into volume of NO2

                          1N2  :  2NO2 mole ratio:               1  :   2 actual moles:         '5'  :  '10' 1---> volume N2= 5dm3  2---> 5x2=10 3---> volume NO2= 10dm3 (No need to use the 24 dm³ factor here since it cancels out.)
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10
Q

What is the concentration of solution?

A

A measure of how much solute is dissolved per unit volume

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11
Q

What is the concentration of a solution measured in?

A

mol/dm3

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12
Q

What is typical lab values (concentration of a solution) ?

A

Between 0.1 and 2.0

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13
Q

What is the formula for concentration of a solution?

A

concentration (mol/dm3) = moles (mol) of solute/ volume (dm3) of solvent

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14
Q

Calculate the concentration when 0.028 moles dissolves into 50 cm3
(Convert cm3 to dm3 and stick the numbers in:)

A

conc (mol/dm3)= moles/vols (dm3)
= 0.028/ (50/1000)
= 0.56mol/dm3

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15
Q

Calculate the moles contained in 230 cm3 of a 0.15 mol/dm3 solution
(Convert cm3 to dm3, rearrange to find moles, then stick the numbers in:)

A

moles= conc (mol/dm3) x vols (dm3)
= 0.15 x (230/1000)
= 0.0345mol

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16
Q

Calculate the volume of a 1.5 mol/dm3
solution that contains 0.2 moles
(Rearrange to find volume, then stick the numbers in:)

A

vols (dm3)= moles/ conc (mol/dm3)
= 0.2/1.5
= 0.133dm3

17
Q

What is titration used for?

A

Titration is a practical method used measure the volume (or ‘titre’) of acid needed to neutralise a particular volume of alkali, or vice-versa.

18
Q

What equipment is used in titration, and what are their functions?

A

1.Volumetric pipette:
-Measures exactly 25 cm³
-Not useful for other volumes

2.Burette:
-Measures any volume to the nearest 0.05 cm³

19
Q

What are the assumptions of the titration procedure?

A
  • The acid is known, so it goes into the burette.
  • The alkali is unknown, so it goes into the conical flask.
  • In reality, it doesn’t matter which one ends up where
20
Q

What are the setup steps for the titration?

A
  1. Use a volumetric pipette to place 25 cm3 of the unknown alkali into a conical flask.
  2. Add a few drops of either methyl orange or
    phenolphthalein indicator to the flask.
    -Universal indicator doesn’t work because it changes colour too gradually.
  3. Fill a burette with known acid and clamp it above the conical flask.
21
Q

What are the usage steps for the titration?

A
  1. Measure the initial volume of known acid on the burette, to the nearest 0.05 cm3
  2. Use the burette to add acid into the conical flask drop-by-drop and swirling the flask.
  3. Close the burette tap as soon as the colour in the conical flask changes.
    -The start colour will be the alkaline colour, the end colour will be the acidic colour (because the last drop of acid always has a tiny amount more than is needed to neutralise).
  4. Measure the final volume of known acid on the burette, to the nearest 0.05 cm3
  5. Calculate titre (final volume − initial volume).
  6. Repeat to get concordant (within 0.2 cm3) titres
22
Q

How do you measure the initial volume of the known acid in the burette?

A

Measure the initial volume to the nearest 0.05 cm³.

23
Q

How should you add acid from the burette into the conical flask?

A

Add acid drop-by-drop while swirling the flask.

24
Q

What should you do when the color in the conical flask changes?

A

Close the burette tap as soon as the color changes from alkaline to acidic.

25
Q

How do you measure the final volume of the known acid in the burette?

A

Measure the final volume to the nearest 0.05 cm³.

26
Q

How do you calculate the titre in a titration?

A

Calculate titre by subtracting the initial volume from the final volume (final volume − initial volume).

27
Q

How should you structure the results table for titration experiments?

A

-table should include columns for the experiment number
-& rows for initial volume (cm³), final volume (cm³), and titre (cm³).

28
Q

How is the mean titre calculated?

A

-based on the concordant titres (within 0.2 cm3)
e.g. mean titre= 20.65 + 20.70/2= 20.675cm3

29
Q

In titration calculations, what do you convert from and to?

A

-You convert from moles of a substance you know a lot about (e.g., the known acid) to moles of a substance you don’t know much about (e.g., the unknown alkali).

30
Q

In a titration, Jenny measured that 20.675 cm3 of 0.1 mol/dm3 H2SO4 was required to neutralise 25 cm3 of NaOH solution - calculate the concentration of the NaOH

A

2NaOH + H2SO4 → Na2SO4 + 2H2O
1. Grid out the numbers in the question:
NaOH : H2SO4
Conc (mol/dm3) ????? : 0.1
Vol (cm3) 25 : 20.675
2. Use your grid to help you do a normal reacting moles calculation:
->Calculate the moles of H2SO4.
->Use the mole ratio from the equation to get the moles of NaOH.
->Calculate the concentration of the NaOH
2NaOH : 1H2SO4
2 : 1
0.004135 : 0.0020675
1—> mol=conc x vol
=0.1x(20.65/1000)
2—> 0.0020675x2=0.004135
3—> conc=mol/vol
=0.004135/(25/1000)= 0.1654 mol/dm3

Chemistry (12 decks)

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