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Flashcards in C2 Calculations and analysis Deck (14)
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1

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

40 + (16 + 1) x 2 = 74

2

Calculate the percentage by mass of calcium in calcium hydroxide

(40 ÷ 74) x 100 = 54%

3

Calculate the mass of calcium in 30g of calcium hydroxide

(54 ÷ 100) x 30 = 16g

4

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

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

5

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

Fe2O3 + 3CO → 2Fe + 3CO2

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

6

What is the formula for percentage yield?

(Actual Yield ÷ Theoretical yield) x 100

7

Give 3 reasons why the yield is not 100%.

Reversible reaction

Product can be lost when separated

Other reactions occur

8

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

% yield = (20 ÷ 40) x 100 = 50%

9

Give 3 reasons why instrumental methods are useful.

Sensitive/ Accurate

Fast

Only needs samples that are small

10

What method can be used to analysis food additives?

Paper Chromatography

11

What is separated in gas chromatography?

Mixture of compounds

12

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

The retention time

13

What can a mass spectrometer be used for?

Gives the relative formula mass

14

What is shown by the molecular ion peak?

Relative formula mass of substance