C2 Calculations and analysis Flashcards

1
Q

Calculate the relative formula mass (Mr) of Calcium hydroxide - Ca(OH)2

A

40 + (16 + 1) x 2 = 74

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2
Q

Calculate the percentage by mass of calcium in calcium hydroxide

A

(40 ÷ 74) x 100 = 54%

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3
Q

Calculate the mass of calcium in 30g of calcium hydroxide

A

(54 ÷ 100) x 30 = 16g

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4
Q

A sample of calcium compound contains 0.8g of calcium, 0.64g of oxygen and 0.04g of hydrogen, find its empirical formula.

A

Mass ÷ Mr

Ca – 0.8 O – 0.64 H – 0.04

40 = 0.02 16 = 0.04 1 = 0.04

Divide by the smallest

Ca – 0.02 O – 0.04 H – 0.04

0.02 = 1 0.02 = 2 0.02 = 2

= CaO2H2

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5
Q

Calculate how much Iron could be made from 320g of Iron oxide

Fe2O3 + 3CO → 2Fe + 3CO2

A

Moles of Fe2O3 = 320 ÷ 160 = Mass ÷ Mr = 2 Moles

Ratio of Fe2O3 1 : Fe 2

Moles of Fe = Moles of Fe2O3 x 2 = 4 Moles

Mass of Fe = Moles of Fe x Mr of Fe = 4 x 56 = 224g

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6
Q

What is the formula for percentage yield?

A

(Actual Yield ÷ Theoretical yield) x 100

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7
Q

Give 3 reasons why the yield is not 100%.

A

Reversible reaction

Product can be lost when separated

Other reactions occur

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8
Q

What is the percentage yield if a reaction only produces 20g when in theory it produces 40g.

A

% yield = (20 ÷ 40) x 100 = 50%

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9
Q

Give 3 reasons why instrumental methods are useful.

A

Sensitive/ Accurate

Fast

Only needs samples that are small

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10
Q

What method can be used to analysis food additives?

A

Paper Chromatography

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11
Q

What is separated in gas chromatography?

A

Mixture of compounds

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12
Q

In the column, what can be used to help identify the substance?

A

The retention time

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13
Q

What can a mass spectrometer be used for?

A

Gives the relative formula mass

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14
Q

What is shown by the molecular ion peak?

A

Relative formula mass of substance

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