Separating Techniques

Question 1

Physical property used in Sieving

Answer 1

Particle size

Question 2

Physical property used in Filtration

Answer 2

One substance a solid, the other a liquid or solution; particle size

Question 3

Physical property used in Vaporisation (evaporation or boiling)

Answer 3

Liquid has a much lower boiling point than the solid (eg. evaporating salt water to get salt)

Question 4

Physical property used in Distillation

Answer 4

Big difference in boiling points (eg. mixture of ethanol with boiling point of 78.37 degrees celsius, and water with a boiling point of 100 degrees celsius)

Question 5

Physical property used in Fractional Distillation

Answer 5

when separating mixtures of liquids with similar boiling points

Question 6

Physical property used in sedimentation and decantation

Answer 6

Components are immiscible liquids; different densities

Question 7

Physical properties when Adding a solvent, then filtering

Answer 7

One substance is soluble in the chosen solvent, while others are insoluble.

Question 8

Pure Substances

Answer 8

Substances which cannot be further separated using physical properties or methods. (not contaminated by any other substances)

Question 9

Mixtures

Answer 9

Two or more pure substances that can be separated using physical properties or methods. (contaminated with small amounts of one or more other substances)

Question 10

Elements

Answer 10

Made of the same atoms. Pure substances that cannot be decomposed into simpler substances (come straight from the periodic table)

Question 11

Componds

Answer 11

Made of two or more different atoms. Pure substance that can be decomposed into simpler substances

Question 12

Homogeneous

Answer 12

uniform composition throughout; composition is evenly distributed no matter which part is sampled (eg. air)

Question 13

Heterogeneous

Answer 13

Has non-uniform composition; when sampled, there will be different properties of a certain pure substance.

Question 14

What is formula Mass?

Answer 14

The sum of the atomic mass of all the atoms in a formula

Question 15

Steps to working out percentage composition

Answer 15

1) Determine the formula mass

2) Determine the mass of each element in the compound

3) % composition = Mass of component in sample (g) / Total mass of sample (g) x 100

Question 16

How is the number of significant numbers determined

Answer 16

In chemistry, the number of significant figures is determined by the value in the question with the smallest number of significant figures.

Question 17

In 0.004004500, is the 0 before the decimal place significant?

Answer 17

No

Question 18

In 0.004004500, are the first two zeros after the decimal point significant?

Answer 18

No

Question 19

In 0.003004500 are the two zeros after 3 significant?

Answer 19

Yes

Question 20

In 0.003004500 are the two zeros at the end to the right of the decimal point significant?

Answer 20

Yes

Question 21

In 0.003004500, are the numbers 3,4 and 5 significant? Why or why not?

Answer 21

Yes, they are significant because any non-zero integers are significant

Question 22

Gravimetrics calculation Question:

A 12.06g sample of hydrated sodium carbonate is heated in a drying oven. The final mass of the sample is 5.81g. Determine the percentage of water in the sample.

Answer 22

Answer = 53.9% (3 sig fig)

solution:
Mass (M) of original sample = 12.06
M of final sample = 5.81g
M of water = 12.60g - 5.81g
= 6.79g

% of water = 6.79 / 12.60 x 100
= 53.9% (3 sig fig)

Question 23

Gravimetrics calculation Question:

Determine the percentage of carbon a sample of brown coal which had an initial mass of 247.5g, and after intense heating to remove all water and other impurities, finally had a mass of 203.4g (assumed to be pure carbon).

Answer 23

Answer: 82.18% (4 sig fig)

Solution:
% of carbon = 203.4g / 247.5g x 100
= 82.18% (4 sig fig)

Question 24

Gravimetric calculation Question:

Upon analysis a 3.67g sample of a certain NPK fertiliser (nitrogen, phosphorus, potassium) was found to contain 1.79g urea and 0.81g ammonium phosphate which the rest being potassium chloride. Calculate the percentage composition of this fertiliser.

Answer 24

Answer:
urea = 49% (2 sig fig)
ammonium phosphate = 22% (2 sig fig)
potassium chloride = 29% (2 sig fig)

solution:
M of sample = 3.67g

M of urea = 1.79g
% of urea = 1.79g / 3.67g x 100
= 49% (2 sig fig)

M of ammonium phosphate = 0.81g
% of ammonium phosphate = 0.81g / 3.67g x 100
= 22% (2 sig fig)

M of potassium chloride = 3.67g - (1.79g + 0.81g)
= 1.07g
% of potassium chloride = 1.07 / 3.67 x 100
= 29% (2 sig fig)

Question 25

Gravimetric Calculation Question: The suitability of water for irrigating crops or for animals to drink depends upon the amount of dissolved solids present. To assess the suitability of water from a particular bore, a grazier took 500g of the water, evaporated it to dryness, then determined the mass of solids remaining to be 3.63g. Calculate the percentage of dissolved solids in this water.

Answer 25

Answer: 0.73% (2 sig fig) Solution: M of original sample = 500g M of solids = 3.63g % of dissolved solids = 3.63g / 500g x 100 = 0.73% (2 sig fig)

Question 26

Gravimetric calculation Question: A certain mineral was a mixture of silver sulphide and zinc sulphide. Upon analysis it was found that 4.62g of mineral contained 1.94g of silver sulphide and 2.68g of zinc sulphide. Calculate the percentage composition of this mineral

Answer 26

Answer: silver sulphide = 42.0% (3 sig fig) zinc sulphide = 58.0% (3 sig fig) solution: M of sample = 4.62g M of silver sulphide = 1.94g % of silver sulphide = 1.94 / 4.62g x 100 = 42.0% (3 sig fig) M of zinc sulphide = 2.68g % of zinc sulphide = 2.68g / 4.62g x 100 = 58.0% (3 sig fig)

Question 27

Atomic radius

Answer 27

Distance from the centre of the nucleus to the outer shell

Question 28

State the trend of atomic radius in a periodic table

Answer 28

Atomic. radius increases down a group and decreases across a period

Question 29

Explain why atomic radius decreases across a period

Answer 29

Atomic radius decreases across a period because elements have more electrons which means there is a greater electrostatic attraction, drawing electrons closer to the nucleus and making the atomic radius smaller.

Question 30

Explain why atomic radius increases down a group

Answer 30

Atomic radius increases down a group because elements have more electrons which means elements have more electron shells, making it bigger thus increasing the atomic radius

Question 31

Ionisation Energy (IE)

Answer 31

Energy required to remove an electron from an atom

Question 32

state the trend in ionisation energy in the periodic table

Answer 32

Ionisation energy decreases down a group, and increases across a period

Question 33

Explain why Ionisation Energy (IE) decreases down a group

Answer 33

IE decreases down a group because atomic radius increases which means there is less electrostatic attraction of electrons to the nucleus, therefore less energy is required to remove the first electron

Question 34

Explain why Ionisation Energy (IE) increases across a period

Answer 34

IE increases across a period because elements have more electrons in the outer shell which means the elements have higher electrostatic attraction due to increasing electronegativity (EN), therefore requiring more energy to be removed.

Question 35

Electronegativity (EN)

Answer 35

Ability of an element to attract the bonding electrons towards itself (how much an element loves its electrons)

Question 36

State the trend of electronegativity in the periodic table

Answer 36

Electronegativity decreases down a group, and increases across a period

Question 37

Why does Electronegativity (EN) increase across a period?

Answer 37

EN increases across a period because there are more electrons as you go across the periodic table, which creates a higher electrostatic attraction to the. nucleus, therefore it draws in its electrons more so towards the nucleus

Question 38

Which element has the highest Electronegativity (EN) in the periodic table

Answer 38

Fluorine has the highest EN on the periodic table

Question 39

Fluoride and chloride are in the same group. Do they have the same electronegativity? Explain your answer

Answer 39

Although Fluorine and Chloride are in the same group, Fluorine has a higher electronegativity than chloride because fluorine has a smaller atomic radius, which means there is a greater electrostatic attraction, therefore, increasing the electronegativity.

Question 40

State the trend of metalic character in the periodic table

Answer 40

Metalic character increases down a group, and decreases across a period

Question 41

Which element has the highest conductivity

Answer 41

Silver

Question 42

How does metalic character relate to its conductivity

Answer 42

As you move across a periodic table,