Separating Techniques Flashcards
Physical property used in Sieving
Particle size
Physical property used in Filtration
One substance a solid, the other a liquid or solution; particle size
Physical property used in Vaporisation (evaporation or boiling)
Liquid has a much lower boiling point than the solid (eg. evaporating salt water to get salt)
Physical property used in Distillation
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)
Physical property used in Fractional Distillation
when separating mixtures of liquids with similar boiling points
Physical property used in sedimentation and decantation
Components are immiscible liquids; different densities
Physical properties when Adding a solvent, then filtering
One substance is soluble in the chosen solvent, while others are insoluble.
Pure Substances
Substances which cannot be further separated using physical properties or methods. (not contaminated by any other substances)
Mixtures
Two or more pure substances that can be separated using physical properties or methods. (contaminated with small amounts of one or more other substances)
Elements
Made of the same atoms. Pure substances that cannot be decomposed into simpler substances (come straight from the periodic table)
Componds
Made of two or more different atoms. Pure substance that can be decomposed into simpler substances
Homogeneous
uniform composition throughout; composition is evenly distributed no matter which part is sampled (eg. air)
Heterogeneous
Has non-uniform composition; when sampled, there will be different properties of a certain pure substance.
What is formula Mass?
The sum of the atomic mass of all the atoms in a formula
Steps to working out percentage composition
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
How is the number of significant numbers determined
In chemistry, the number of significant figures is determined by the value in the question with the smallest number of significant figures.
In 0.004004500, is the 0 before the decimal place significant?
No
In 0.004004500, are the first two zeros after the decimal point significant?
No
In 0.003004500 are the two zeros after 3 significant?
Yes
In 0.003004500 are the two zeros at the end to the right of the decimal point significant?
Yes
In 0.003004500, are the numbers 3,4 and 5 significant? Why or why not?
Yes, they are significant because any non-zero integers are significant
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 = 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)
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: 82.18% (4 sig fig)
Solution:
% of carbon = 203.4g / 247.5g x 100
= 82.18% (4 sig fig)
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:
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)
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: 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)
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:
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)
Atomic radius
Distance from the centre of the nucleus to the outer shell
State the trend of atomic radius in a periodic table
Atomic. radius increases down a group and decreases across a period
Explain why atomic radius decreases across a period
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.
Explain why atomic radius increases down a group
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
Ionisation Energy (IE)
Energy required to remove an electron from an atom
state the trend in ionisation energy in the periodic table
Ionisation energy decreases down a group, and increases across a period
Explain why Ionisation Energy (IE) decreases down a group
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
Explain why Ionisation Energy (IE) increases across a period
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.
Electronegativity (EN)
Ability of an element to attract the bonding electrons towards itself (how much an element loves its electrons)
State the trend of electronegativity in the periodic table
Electronegativity decreases down a group, and increases across a period
Why does Electronegativity (EN) increase across a period?
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
Which element has the highest Electronegativity (EN) in the periodic table
Fluorine has the highest EN on the periodic table
Fluoride and chloride are in the same group. Do they have the same electronegativity? Explain your answer
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.
State the trend of metalic character in the periodic table
Metalic character increases down a group, and decreases across a period
Which element has the highest conductivity
Silver
How does metalic character relate to its conductivity
As you move across a periodic table,
