pp Flashcards
(35 cards)
Test Ammonium chloride for ammonium ions
Adding sodium hydroxide solution results in the production of ammonia gas
This can be tested by either method; the gas will change the colour of damp litmus paper as it is an alkaline gas or react with concentrated HCl to make a white ‘smoke’ of ammonium chloride (as the formed crystals of the salt are tiny and are suspended in the air when formed in this way
A student has two solids, X and Y.
One ofthese solids is a pure substance and the other is a mixture.
Describe how the student could identify which solid is pure and which is a mixture by measuring a physical property of
each solid.
The purity of a solid is tested by measuring the melting point
A narrow / tight temperature range for the melting point indicates that it is pure
A broad / wide temperature range for the melting point indicates that it is not pure
The purity of a liquid is tested by measuring the boiling point
A narrow / tight temperature range for the boiling point indicates that it is pure
A broad / wide temperature range for the boiling point indicates that it is not pure
Give the charge on the lead ion in Pb(NO3)2
2+
MP when impurity is added
over a rane of temps
chromotogrophy-most soluble dye
largest Rf value, moves most in solvent
A studentinvestigates the solubility of potassium nitrate in water. She measures the masses of potassium nitrate that
dissolve in 25 cm of water at differenttemperatures.
2 reasons for anoamolous result?
Less than 25 cm3 of water was used; [1 mark]
The temperature was less than 50 oC; [1 mark]
Not enough potassium nitrate was added; [1 mark]
The solution was not stirred; [1 mark]
mobile and stationary in chromotog.
- mobile; mlecules can move in substance(e.g: solvent)
- stationary: substance molecules cannot move, e.g:solid, thick liquid, paper in chromo
silver chloride is
white
chromotogrophy fair test
Use of pencil for the start line / baseline; [1 mark]
All spots on the start line / baseline; [1 mark]
Same distance travelled by the solvent / water; [1 mark]
Give an advantage of mixing solutions containing equal amounts, in moles, of silver nitrate and sodium chloride
To ensure the silver nitrate and sodium chloride are fully reacted; [1 mark]
To ensure the reactants are all reacted / nothing is left unreacted; [1 mark]
So that neither reagent is in excess; [1 mark]
To make sure the products only contained silver chloride and sodium nitrate; [1 mark]
To ensure the highest possible yield; [1 mark]
To ensure that the sodium nitrate (crystals) are pure; [1 mark]
If either chemical was in excess, then this would contaminate the sodium nitrate (crystals); [1 mark]
The students make the following incorrect or incomplete conclusions:
Student1 states thatthe substance is fluorine, neon or sodium
Student 2 states thatitis not possible to determine which atom or ion the diagram represents
Student 3 states thatthe mass number is 10
Explain how students 1 and 2 could combine their ideas to produce one possible correct conclusion with an appropriate
justification
The key point hiding in this question is whether this diagram represents an atom or an ion (student 2)
By stating the word atom, student 2 narrows the possible options of student 1 to a single answer
An atom with 10 electrons
Therefore, they could make a correct combined statement that the diagram represents an atom of neon because it contains 10 electrons
By stating the word ion, student 2 narrows the possible options of student 1 to two possible answers
An ion with 10 electrons
Therefore, they could make a combined statement that the diagram represents an ion of fluorine or sodium because it contains 10 electrons
Since the question asks for one possible conclusion / identity, you have to focus on the atom idea not the ion idea
5b
The term isotope means:
Atoms (of the same element) with the same number of protons
OR
Atoms (of the same element) with the same atomic number; [1 mark]
But different numbers of neutrons; [1 mark]
correct the child
Student 3 states thatthe mass number is 10
a diagram with a circle nucleus and 10 e- in shells
Student 3 could be corrected by:
Stating that the proton number is 10; [1 mark]
There is no charge shown in the diagram; [1 mark]
So, 10 electrons mean 10 protons
AND
(Because,) atoms are electronically neutral / have no overall charge; [1 mark]
Helium is now used in airships instead of hydrogen because:
Helium is inert / unreactive
OR
Helium does not react (with air / oxygen); [1 mark]
Hydrogen is flammable / explosive (in air / oxygen); [1 mark]
A catalyst is used in this reaction because:
It increases the rate of reaction / speeds up the reaction
OR
It produces / uses a reaction pathway with a lower activation energy
OR
It lowers the activation energy
OR
It makes it easier to break the (covalent) bonds; [1 mark]
) Hydrogen should not be placed in Group 1 because:
Any two from:
Hydrogen is a non-metal
OR
Group 1 elements are metals; [1 mark]
Hydrogen does not react similarly to the other Group 1 elements
OR
Hydrogen does not react with water
OR
Group 1 elements react with water; [1 mark]
(At room temperature and pressure) hydrogen is a gas
OR
(At room temperature and pressure) Group 1 elements are solids; [1 mark]
Hydrogen can form a negative ion
OR
Hydrogen can gain an electron
OR
Group 1 elements form positive ions
OR
Group 1 elements lose an electron; [1 mark]
Hydrogen can form covalent bonds
OR
Hydrogen can share electrons
OR
Group 1 elements form metallic bonds
OR
Group 1 elements transfer electrons; [1 mark]
H can be in g7 cuz
It exists as a diatomic molecule; [1 mark]
It forms covalent bonds/compounds; [1 mark]
It is able to form H– ions; [1 mark]
It has a low melting / boiling point; [1 mark]
The modern Periodic Table arranges the elements in order of atomic number.
What scientific discoveries allowed elements to be placed in their correct period and group?
How did this knowledge allow elements to be correctly placed?
The scientific discoveries that led to elements being placed in the correct group and period are:
Electrons
AND
Protons; [1 mark]
The discovery of these enabled the elements to be placed in their correct places because:
Any three from:
The number of protons gives the atomic number; [1 mark]
The number of protons equals the number of electrons; [1 mark]
Elements in the same group have the same number of outer electrons; [1 mark]
Reactivity / (chemical) properties depend on the number of (outer) electrons; [1 mark]
The number of (electron) shells gives the period; [1 mark]
why layers can slide over e/o
There are no bonds between adjacent atoms / ions; [1 mark]
So the atoms / ions can slide over each other;
Give two other physical properties of potassium.
(2)
Give one chemical property of potassium.
One other physical property of potassium is:
Any two from:
Low density; [1 mark]
Low melting point; [1 mark]
(Good) conductor (heat or electricity); [1 mark]
Shiny (when freshly cut); [1 mark]
Malleable; [1 mark]
Ductile; [1 mark]
ii) One chemical property of sodium is:
Any one from:
Very reactive; [1 mark]
Reacts with water (not steam); [1 mark]
Forms salts with halogens; [1 mark]
React vigorously with acids; [1 mark]
Forms an alkaline or basic oxide; [1 mark]
Has one valency or outer shell electron so does not form ionic compounds on its own; [1 mark]
[Total: 3 marks]
why have high MP sumn?
giant structure(u keep forgetting this)
The conditions in which potassium oxide can conduct electricity are:
When aqueous / in solution; [1 mark]
When molten / melted / as a liquid; [1 mark]
(Because) the ions can move and carry a charge; [1 mark]
[Total: 3 marks]
why water can carry elecricit
cuz ions dissolved in the water
NaOH electrolysis
at catchode
For concentrated aqueous sodium chloride:
The ions present are: Na+, H+, Cl-, and OH–
Hydrogen is less reactive than sodium so hydrogen ions are discharged at the cathode where they are reduced to hydrogen gas :
2H+ + 2e- → H2
The chlorine has been discharged at the anode
The Na+ and OH– have remained in solution to form sodium hydroxide, NaOH
