Quantative Analysis

Question 1

What is the mass of 0.1 mole of sulfur dioxide.
(Oxygen = 16) (sulfur = 32)

Answer 1

16 x 2 = 32
32 + 32 = 64
64 x 0.1 = 6.4

Question 2

What mass of magnesium oxide should be formed, (theoretical yield) when 2.4g of Mg reacts with 1.6g of O

Answer 2

2.4 + 1.6
4 grams

Question 3

Calculate the percentage yield when theoretical yield is 4g and the theoretical yield is 3.3g.

Answer 3

3.3 ÷ 4 = 0.825
0.825 × 100 = 82.5

82.5%

Question 4

What is the formula for atom economy?

Answer 4

Atom economy = (rfm of the useful product ÷ sum of rfm of all the reactants) ×100

Question 5

What is the atom economy for making ammonia using nitrogen and hydrogen? N² + H⁶ = 2(NH³)

Answer 5

N² = 28
H⁶ = 6
NH³ = 17 17 × 2 = 34
Useful product equals 34
All reactants equal 34
34 ÷ 34 =1 1×100 = 100%

100%

Question 6

How many moles are there in 66g of carbon dioxide. CO² C = 12 O = 16

Answer 6

12 + (16 ×2) = 44
66g ÷ 44 = 1.5 moles

Question 7

What is the formula for concentration?

Answer 7

Mass of solute(g) ÷ volume of solution(dm³)
= concentration (g dm-3)

Dm is to the power of neg 3

Question 8

25g of sulafte is dissolved in 500cm³ of water. What is the concentration in g dm-3

Answer 8

500 ÷ 1000 = 0.5 dm³
25 ÷ 0.5 = 50 gdm -3

Question 9

What mass of sodium chloride is in 300cm³ of solution with a concentration of 12g dm-3?

Answer 9

300 ÷ 1000 = 0.3 dm³
12 × 0.3 = 3.6
3.6g of sodium chloride

Question 10

What is avogadro’s constant?

Answer 10

6.02 x10²³

Question 11

Calculate the number of moles in 90g of water. Rfm = 18

Answer 11

90 ÷ 18 = 5
5 moles

Question 12

Calculate the mass of 0.200 moles of potassium bromide. Rfm of KBr = 119

Answer 12

119 x 0.2 = 23.8 moles

Question 13

What mass of sodium hydroxide is contained in 200cm³ of a 55g dm-³ solution?

Answer 13

200 ÷ 1000 = 0.2 dm³
0.2 × 55 = 16.5
11g

Question 14

What is the difference between chemical and empirical formulas?

Answer 14

Chemical formulas state the actual amount of atom of each element.
Empirical formulas state the smallest whole number ratio of the atoms

Question 15

A sample of hydrocarbon contains 36g of carbon and 6g of hydrogen. Work out the empirical formula.
C = 12
H = 1

Answer 15

36g ÷ 12 = 3
3 moles of carbon
6 ÷ 1 = 6
6 moles of hydrogen
3 ÷ 3 = 1 Carbon
6 ÷ 3 = 2 Hydrogen
CH²

Question 16

practical to find metal ions present

(flame test)

Answer 16

light Bunsen to blue flame (open air hole )

clean loop with HCl

pick small sample of test using loop

hold the loop with smample to edge of flame and observe colour

Question 17

how would u make the flame test more accurate
and how

Answer 17

by using a flame photomerty

.sensitivity- can detect smaller amounts
.accuracy-can give value closer to he true value
speed

Question 18

test for metal ions

what colour flame would you see for each ion present

Answer 18

lithium Li+ red
sodium Na+ yellow
potassium k+ lilac
calcium2+ Orange-red
copper2+ blue-green

Question 19

What is a mole?

Answer 19

1 mole is 6.02 x10²³ particles
1 moles of Oxygen gas(o²) weighs 32g
1 mole is also equal to the ram of a substance
To work out moles you do mass(g) divided by ram.
72 grams of oxygen gas would be 2 moles
72 grams of oxygen(O) would be 4 moles

Question 20

8.1g of zinc oxide reacts with 0.3g of carbon. The balanced chemical reaction is
2 ZnO + C -> CO² + 2 Zn

Answer 20

First work out moles.
Moles of zinc = 8.1 ÷ 81(ram) = 0.1 mol
Moles of Carbon = 0.3 ÷ 12 = 0.025 mol
The ratio of moles in terms of mass is 4 to 1. The ratio of moles needed for the reaction is 2 to 1. There is an excess amount of Zinc oxide.

Carbon is the limiting reactant

Question 21

how to work out concentration
using volume of solution (g dm3)

Answer 21

concentration (g dm3-) / volume of solution (dm-3)

Question 22

how to work out concentration with moles
(mol dm3-)

Answer 22

moles(mol)/ volume (dm3)

Question 23

how to work out concentration when given the mr of solute (mol dm3-)

Answer 23

conc/mr

Question 24

concentraion when given mass
(g dem-3)

Answer 24

mass/volume

Question 25

how to work out amount (mol)

Answer 25

volume (dm3) / molar volume (24)