topic 4 - inorganic Flashcards by Roukaya Elkomy

A white solid was thought to be barium carbonate. A student suggested that the presence of the carbonate ion could be tested for by adding a small amount of sulfuric acid.
Explain whether or not this suggestion is valid. (2)

-usually carbonates react with acids to produce a colorless gas/CO2
-But the Barium sulfide produced is insoluble so the carbonate ion may appear to not react

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Explain how the trend in the reactivity of the group 2 elements is determined by their electronic configurations (3)

-the outer electrons are further from the nucleus
-There is more shielding or there is an increase in repulsion between the filled inner shells and the electron removed
-So the first ionistation energy decreases down the group AND so the reactivity increases

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describe how to carry out a flame test (3)

nichrome wire
dip the wire into concentrated hydrochloric acid
dip the wire into the solid and place IN a flame

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Explain wether magnesium carbonate is more or less thermally stable than barium carbonate (3)

the magnesium ion has a greater charge density
So more likely to polarize the carbonate ion
And so weaken the C-O bond

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write an equation for the thermal decomposition of lithium nitrate (1) 

4LiNO3 —> 2Li2O + 4NO2 + O2

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state one reason why an experimental gas volume may differ from the calculated theoretical volume.
assume that no gas escapes and measurements have been made accurate. (1)

incomplete reaction/decomposition

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explain why group 1 carbonates are more thermally stable than group 2 carbonates (3)

group 2 ions have larger charge or group 2 ions have a 2+ charge and group 1 ions have a 1+ charge
Group 2 ions polarize bonds in the carbonate ion more
The C-O bond is weakened

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explain the origin of flame test colors (4)

heat from flame
electrons promoted to higher energy levels
electrons drop down to lower energy levels
light in the visible region is emitted

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give a reason why the magnesium ion does not produce a flame color (1)

no emission of light in the visible region of the spectrum

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give a reason why the lack of a flame color is not a positive test for the magnesium ion (1)

there are other ions that do not produce a flame color

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explain why magnesium nitrate decomposes more readily on heating than potassium nitrate (4)

magnesium ion is smaller
magnesium ion has a higher charge
magnesium ion polarises nitrate ion more
so weakening the N-O bonds more

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explain how atoms of different elements can produce different characteristic flame colors when heated (4)

electrons move up energy levels
Electrons return to a lower energy level
Energy emitted from the atom as visible light
Different energy emitted in different elements so different colors emitted

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Give a reason why carrying out a flame test on a mixture of potassium chloride and strontium chloride does not clearly show that two different metal ions are present (1)

The red color will mask the lilac color

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give two reasons why the wire is made of nichrome and not iron (2)

nichrome produces no color or iron can produce a color
nichrome is unreactive

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give a reason why the wire is dipped into acid and then heated in the first stage (1)

to remove the residue of any previous sample being tested

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state why fresh concentrated hydrochloric acid is used in the second stage of the flame test (1)

the acid can become contaminated with residue from previous tests

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state why hydrochloric acid is used in the second stage of the flame test (1)

concentrated HCL forms volatile chlorides

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state two observations you would see when hydrated magnesium nitrate is heated (2)

solid dissolved/melts
condensation on sides of test tube
brown gas produced (NO2)
white solid

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explain the trend in thermal stability of group 2 nitrates (3)

nitrates increase in stability down group 2 as ionic radius increases
so polarizing ability of metal deacreases
weakening the N-O bonds less

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name all the types of bond present in calcium carbonate (1)

Ionic and covalent

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give a reason, in terms of bonding, why a high decomposition temperature is required to decompose calcium carbonate (1)

strong bonds within the carbonate ion

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state one observation when magnesium reacts with steam (1)

white powder

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describe the bonding in magnesium (2)

attraction between Mg2+ ions
and delocalized electrons

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explain in terms of structure and bonding why magnesium chloride has a high melting point (3)

giant ionic lattice
strong forces of attraction
between Mg2+ and Cl- ions

explain why the melting point of magnesium is higher than the melting point of sodium (2)

Mg2+ has a higher charge than Na+ stronger attraction to delocalized sea of electrons

explain why the second ionization energy of calcium is lower than the second ionization energy of potassium (2)

in Ca electron is further from nucleus more shielding

identify the s-block metal that has the highest first ionization energy (1)

beryllium

explain why the melting point of calcium sulfate is high (2)

strong attraction between positive and negative ions

give a reason why chlorine is added to water (1)

- kills bacteria

Describe a chemical test, and the expected result, to show that sulfate ions are present in a solution of iron(ll) sulfate in water (2)

add hydrochloric acid then add barium chloride White percipitate/solid

an aqueous solution is suspected to be potassium bromide and it is tested for the presence of the anion. (i) write the name of the reagent used to test for the anion (1) (ii) state the expected result of this test and the formula of the product (2)

(i) silver nitrate (ii) cream percipirtate and AgBr

state why no reaction occurred between potassium bromide and aqueous iodine (1)

iodine cannot oxidise bromide ions

Explain why the boiling temperatures increase from chlorine to iodine (2)

from chlorine to iodine, the number of electrons increases So there are more London forces AND more energy is needed to separate the molecules

determine a test to confirm the identity of the anion in a cream precipitate (2)

add dilute ammonia and the ppt is insoluble Add concentrated ammonia and the ppt is soluble

a different ion containing chlorine is formed if the solution of aqueous hydroxide ions is hot. give the formula of the chlorine containing ion and the oxidation number of chlorine in this ion (2)

ClO3- +5

Hydrogen chloride gas dissolves in water to form hydrochloric acid Hydrogen chloride gas does not conduct electricity Hydrochloride acid is a good conductor of electricity Give a reason for this change in conductivity (1)

the covalent bond in hydrogen changes to an ionic bond in aqueous solution

Hydrochloric acid is added to a test tube containing a sample of solid sodium carbonate Give two observations (2)

White solid dissolves bubbles

Bromide can be extracted from seawater containing bromide ions using chlorine Write the ionic equation for this reaction (1)

Cl2 + 2Br- —> 2Cl- + Br2

Give a reason why dilute HCl is needed before adding barium chloride when testing for sulphate ions (1)

To react with any carbonate ions

On descending group 7, the hydrogen halides become better reducing agents. Explain how the reactions of potassium chloride, potassium bromide and potassium iodide with concentrated sulphuric acid provide evidence for this statement (3)

sulphur in sulphuric acid is reduced further by hydrogen iodide than hydrogen bromide and hydrogen chloride SO2 produced in the reaction with HBr More negative oxidation states of sulphur are produced in the reaction with HI

give the reagent and the observation to show the presence of carbonate ions and sulfate ions (4)

carbonate: add sulfuric acid and bubbling sulfate: add barium chloride and white ppt forms

describe how you would show that iodide ions are present in an aqueous solution of potassium iodide (2)

add silver nitrate and nitric acid yellow precipitate

describe how London forces form between halogen molecules (3)

uneven distribution of electrons results in an instantaneous/temporary dipole induces a dipole on another molecule

explain why bromine has a higher boiling temperature than chlorine (2) 

bromine has more electrons bromine has stronger London forces

give the physical states of chlorine and iodine at room temperature and pressures (1) 

chlorine is a gas iodine is a solid

predict the physical state of astatine under these conditions. justify your answers (1)

astatine is a solid and as number of electrons increase, strength of London forces increases

chlorine has a low b.p because the forces between the molecules are weak. Explain how these forces arise between molecules of chlorine (3)

temporary dipole is formed in one molecule induces a dipole in a neighbouring molecule these temporary dipoles attract

give an equation from the reaction of chlorine with water and a reason why it is added to water (2)

Cl2 + H2O -> HCl + HClO kills bacteria

chlorine reacts with cold, aqueous sodium hydroxide in the manufacture of bleach. give an equation for this reaction (1)

Cl2 + 2NaOH -> NaCl + NaClO + H2O

give an equation for the reaction of solid sodium bromide with concentrated sulfuric acid to form bromide state one observation made during this reaction. (2)

2H2SO4 + 2NaBr -> Na2SO4 + SO2 + Br2 + 2H2O orange/brown fumes/solution

Give one reason why water is treated with chlorine Give an equation for the reaction of chlorine with drinking water Explain why chlorine is added to water even though its toxic (3)

reason: kill bacteria equation: Cl2 + H2O -> HCl + HClO explanation: health benefit outweighs the risk/low concentrations used

state what is observed when silver nitrate solution is added to sodium fluoride solution (1)

colorless solution

state one observation when solid sodium chloride reacts with concentrated sulfuric acid give an equation for the reaction state the role of the chloride ions in the reaction (3)

white gas NaCl + H2SO4 -> NaHSO4 + HCl or with 2 infront of Nacl and + 2HCl in the end base or proton acceptor

state what is observed when aqueous chlorine is added to sodium bromide solution give an ionic equation for the reaction (2)

yellow or orange solution Cl2 + 2Br- —> 2Cl- + Br2

bromine, strontium chloride and iodine monochloride all have similar Mr values. Suggest with reasons the order of melting poins for these three substances (6)

SrCl2 > ICl > Br > SrCl2 strong ionic bonds lattice so many strong bonds to overcome ICl has dipole-dipole between molecules - weaker than ionic bonds Br2 has London forces between molecules - much weaker

Explain why magnesium nitrate, Mg(NO3)2 decomposes more readily on heating than potassium nitrate, KNO3. ( 4 )

- magnesium ion is smaller (than the potassium ion) (1) - magnesium ion has a higher charge (than the potassium cation)/ Mg ion is 2+ but K ion is 1+ (1) - magnesium ion polarises nitrate (ion more) / distorts the (electron cloud of) nitrate (ion more) (1) - so weakening the N−O bonds (more) / so weakening the nitrate bonds (more)

colour change of phenolphthalein indicator

colourless to pale pink

what does rate of decomposition depend on

- metal ion size - charge density

discuss how the student can use observations from the experiment ( decomposition of carbonates ) and knowledge of the cations present in the carbonates , to justify the relative rate of decomposition

- cloudiness/ milkiness / formation of white ppt due to the reaction of limewater and CO2 - the shorter the time for limewater to go cloudy , the faster the rate of decomposition - rate of decomposition depends on metal ion size and charge density - Mg2+ has smaller radius than Ca2+(smaller is faster) - Mg2+ has greater charge density than Li+ ( greater charge density is faster ) - C does not decompose as K+ has a relatively large radius and small charge