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ISA Skills > Chem > Flashcards

Chem Flashcards

0
Q

Empirical formula

A

The simplest whole number ratio of atoms of each element in a compound.

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1
Q

Molecular formula

A

Actual number of atoms of each element in a molecule

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2
Q

General formula

A

The simplest algebraic formula for a member of a homologous series.

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3
Q

Structural formula

A

The minimum detail that shows the arrangement of the atoms in a molecule

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4
Q

Displayed formula

A

Shows the relative positioning of the atoms and the bonds between them

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5
Q

Avogadro constant

A

The number of atoms in 12g of carbon 12.

6.022x10-23

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6
Q

How can you reduce errors in measuring mass?

A

Use a more accurate balance

Larger mass

Weighing sample before and after addition and then calculating the difference will ensure a more accurate measurement of the mass added.

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7
Q

What does it mean if the percentage error due to the apparatus is less than the percentage difference between the actual value and the calculated value?

A

There is a discrepancy in the result due to other errors

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8
Q

If the percentage error due to the apparatus is greater than the percentage difference between the actual value and the calculated value?

A

There is no discrepancy and all errors in the results can be explained by the sensitivity of the equipment

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9
Q

How can you decrease apparatus error?

A

Decrease the sensitivity error by using apparatus with a greater resolution.

Increase the size of the measurements made

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10
Q

Cm^3 to Dm^3

A

Divide by 1000

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11
Q

Cm^3 to m^3

A

Divide by 1,000,000

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12
Q

Dm^3 to m^3

A

Divide by 1000

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13
Q

How do you get concentration in gdm^-3

A

Concentration in mol dm^-3 x Mr of the substance

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14
Q

Percentage yield

A

Actual yield/ theoretical yield

X100

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15
Q

Percentage atom economy

A

Mass of useful products/mass of all reactants

X100

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16
Q

Irritants

A

Dilute acid and alkalis

Must wear googles

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17
Q

Corrosive

A

Stronger acids and alkalis

Wear googles

18
Q

Flammable

A

Keep away from naked flames

19
Q

Toxic

A

Wear gloves
Avoid skin contact
Wash hands after use

20
Q

Oxidising

A

Keep away from flammable/ easily oxidised materials

21
Q

Why should large amounts of zinc sulphate not be used?

A

Decomposition is likely to be incomplete

22
Q

Why does the crucible need to be dry?

A

A wet crucible would give an inaccurate result.

It would cause mass loss to be too large as water would be lost when heating.

23
Q

How does the lid improve the accuracy?

A

Prevents loss of solid from the crucible but should be loose fitting to allow gas to escape.

24
Q

Why should small amounts of solid not be used?

A

The errors in weighing are too high

25
Q

What is concentration in gdm^3 the same as?

A

The mass of the solute dissolved in 1dm^3

26
Q

When is a gas syringe usually used?

A

To work out moles of gas

To follow reaction rates

27
Q

What should you do when recording volume?

A

Note down the temperature and pressure of the room

28
Q

What two things are important when drawing a diagram?

A

Don’t leave gaps in the diagram where the gas could escape

Draw the gas syringe with measurements on it

29
Q

Potential errors when using a gas syringe

A

Gas escapes before bung is inserted

Syringe sticks

Some gases like carbon dioxide and sulphur dioxide are soluble in water so the true amount of gas is not measured.

30
Q

Improving accuracy when weighing solutions?

A

Weighing bottle again after it has been emptied into the beaker.

The weighing bottle could be washed and washings added to the beaker

Fill so the bottom of the meniscus sits on the line on the neck of the flask

31
Q

Why is a white tile used underneath the flask?

A

To help observe the colour change.

32
Q

What precautions should you take if you are working with an unknown substance?

A

Treat the substance as potentially toxic and wear gloves.

33
Q

Why is a conical flask used in preference to a beaker?

A

It is easier to swirl the mixture in a conical flask without spilling the contents.

34
Q

How can distilled water be used in a titration?

A

It can be added to a conical flask during a titration to wash the sides of the flask so that all the acid on the side is washed into the reaction mixture to react with the alkali.

35
Q

Why does distilled water not affect the titration reading?

A

Water does not react with the reagents or change the number of moles of acid added.

36
Q

What can we say about the results if our data is concordant?

A

The results are accurate and reproducible and the titration technique is good/consistent.

37
Q

What is important to consider when titrating mixtures?

A

If the mixture contains other substances that have acid based properties.

38
Q

Why is it important to do titrations on several samples in quality control?

A

The amount/ concentration of the chemical being tested may vary between samples.

39
Q

Why is magnesium hydroxide suitable for dealing with excess stomach acid?

A

It has a low solubility in water and is only weakly alkaline so not corrosive or dangerous to drink.
It does not produce any carbon dioxide gas.

40
Q

Relative atomic mass

A

The average mass of one atom compared to one twelfth the mass one atom of carbon 12

41
Q

How do you calculate percentage error?

A

Sensitivity error/ measurement made on apparatus

x by 100

42
Q

How do you calculate the maximum percentage error?

A

add all the individual equipment errors together

43
Q

How can you reduce errors in a titration?

A

Replacing measuring cylinders with pipettes or burettes which have lower apparatus sensitivity error will lower the error.
To reduce the error in a burette reading it is necessary to make a titre a larger volume. This could be done by: increasing the volume and concentration of the substance in the conical flask or by decreasing the concentration of the substance in the burette.
Fill the jet space prior to commencing the titration as it would lead to errors otherwise as it will fill during the titration. This will lead to a larger than expected titre reading.

ISA Skills (1 decks)

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