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schewl >_< > science C4 > Flashcards

science C4 Flashcards

1
Q

Give the value for Avogadro’s constant.

A

6.02×1023

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2
Q

Which formula is used to calculate the number of moles from mass and Mr ?

A

moles = mass/Mr

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3
Q

Which formula is used to calculate the mass of a substance from number of moles and Mr ?

A

mass = moles × Mr

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4
Q

What is a limiting reactant?

A

the reactant that is completely used up in a chemical reaction

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5
Q

What is a unit for concentration?

A

g/dm3 or mol/dm3

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6
Q

Which formula is used to calculate concentration from mass and volume?

A

concentration (g/dm3) = mass (g) /
volume (dm3)

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7
Q

Which formula is used to calculate volume from concentration and mass?

A

volume (dm3) = mass (g)
/ concentration (g/dm3)

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8
Q

Which formula is used to calculate mass from concentration in g/dm3
and volume?

A

mass (g) = concentration (g/dm3) × volume (dm3)

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9
Q

How can you convert a volume reading in cm3 to dm3 ?

A

divide by 1000

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10
Q

If the amount of solute in a solution is increased, what happens to its concentration?

A

increases

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11
Q

If the volume of water in a solution is increased, what happens to its concentration?

A

decreases

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12
Q

What is the yield of a reaction?

A

mass of product obtained from the reaction

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13
Q

What is the theoretical yield of a reaction?

A

maximum mass of the product that could have been produced

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14
Q

Why is the actual yield always less than the theoretical yield?

A

reaction may be reversible
some of the product can be lost on separation unexpected side reactions between reactants

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15
Q

What is the percentage yield?

A

actual yield as a proportion of theoretical yield

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16
Q

How is percentage yield calculated?

A

actual yield / theoretical yield × 100

17
Q

What is atom economy?

A

measure of how many atoms of the reactants end up as useful products

18
Q

Why is a high atom economy desirable?

A

it uses fewer natural resources, produces less waste, and is better for the environment.

19
Q

How is percentage atom economy calculated?

A

Mr of useful product / Mr of all products × 100

20
Q

How can concentration in mol/dm3 be calculated?

A

moles of solute / volume (dm3)

21
Q

What is a titration?

A

method used to calculate the concentration of an unknown solution

22
Q

What is the end-point?

A

the point at which the reaction is complete (when the indicator changes colour) and no substance is in excess

23
Q

How should solution be added from the burette close to the end point?

A

drop by drop, swirling in between

24
Q

Why is a white tile used in titration?

A

to see the colour change better

25
Q

What is a titre?

A

volume of solution added from the burette

26
Q

What volume does one mole of any gas occupy at room temperature and pressure?

A

24dm3 or 24 000 cm3

schewl >_< (23 decks)

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