Quick Review Flashcards - Click to flip and test your knowledge!
Question
In which group and period of the periodic table is the element Hydrogen ($H$) placed?
Answer
Hydrogen is placed in Group 1 ($IA$) and Period 1.
Question
What is the atomic number and the number of valence electrons for Hydrogen?
Answer
The atomic number is 1, and it has 1 valence electron.
Question
Why is Hydrogen considered to have a 'dual nature' regarding its position in the periodic table?
Answer
It shows similarities to both Alkali metals (Group 1) and Halogens (Group 17).
Question
What electropositive ion is formed when Hydrogen behaves like an alkali metal?
Answer
It forms the Hydrogen ion ($H^{1+}$) by losing one electron.
Question
What electronegative ion is formed when Hydrogen behaves like a halogen?
Answer
It forms the Hydride ion ($H^{1-}$) by gaining one electron.
Question
Which scientist first prepared hydrogen in its pure state and recognized it as an element in 1776?
Answer
Henry Cavendish.
Question
Who established the name 'hydrogen' and what does the Greek word mean?
Answer
Lavoisier established the name, which means 'water producer'.
Question
What is the approximate abundance of Hydrogen by mass in the Earth's crust?
Answer
Hydrogen makes up approximately $1\%$ of the Earth's crust.
Question
By mass, what fraction of water is composed of hydrogen?
Answer
About one-ninth of the mass of water is hydrogen.
Question
What are the two products formed when Potassium ($K$) reacts with cold water?
Answer
Potassium hydroxide ($KOH$) and Hydrogen ($H_2$).
Question
Why is the reaction of Sodium ($Na$) or Potassium ($K$) with cold water not preferred for laboratory hydrogen preparation?
Answer
The reaction is violent and exothermic, potentially igniting the liberated hydrogen.
Question
What metallic product is formed when Magnesium ($Mg$) reacts with boiling water?
Answer
Magnesium oxide ($MgO$).
Question
Which three metals react with steam in a heated state to form metallic oxides and hydrogen?
Answer
Aluminium ($Al$), Zinc ($Zn$), and Iron ($Fe$).
Question
What is the chemical formula for the 'magnetic oxide of iron' produced when iron reacts with steam?
Answer
$Fe_3O_4$.
Question
Why is the reaction between red-hot iron and steam described as reversible?
Answer
The products ($Fe_3O_4$ and $H_2$) can react under certain conditions to reform the original reactants ($Fe$ and $H_2O$).
Question
Why is dilute nitric acid ($HNO_3$) not used in the laboratory preparation of hydrogen from metals?
Answer
It is a powerful oxidising agent that oxidises the hydrogen formed into water.
Question
Why can Lead ($Pb$) not be used to prepare hydrogen using dilute hydrochloric or sulphuric acid?
Answer
An insoluble coating of lead chloride or lead sulphate forms, stopping the reaction.
Question
What is the salt produced when Zinc ($Zn$) reacts with hot concentrated Sodium hydroxide ($NaOH$)?
Answer
Sodium zincate ($Na_2ZnO_2$).
Question
Which metals exhibit an 'amphoteric nature' by reacting with both acids and alkalis to produce hydrogen?
Answer
Zinc ($Zn$), Lead ($Pb$), and Aluminium ($Al$).
Question
What are the reactants used in the standard laboratory preparation of hydrogen gas?
Answer
Granulated zinc and dilute hydrochloric acid (or dilute sulphuric acid).
Question
Why is 'granulated zinc' preferred over pure zinc in laboratory preparation?
Answer
It contains traces of impurities (like copper) which act as a catalyst to speed up the reaction.
Question
What method is used to collect hydrogen in the laboratory, and why?
Answer
Downward displacement of water, because hydrogen is almost insoluble in water.
Question
Why is hydrogen not collected by the downward displacement of air, despite being lighter than air?
Answer
It forms an explosive mixture with air.
Question
Which impurity is removed from laboratory-prepared hydrogen by passing it through silver nitrate solution?
Answer
Arsine ($AsH_3$) and phosphine ($PH_3$).
Question
Which substance is used as a drying agent to remove moisture from hydrogen gas?
Answer
Fused calcium chloride.
Question
What is the first step of the Bosch Process, involving the production of 'water gas'?
Answer
Passage of steam over white-hot coke (carbon) at around $1000^\circ\text{C}$.
Question
In the Bosch Process, what is 'water gas' a mixture of?
Answer
Carbon monoxide ($CO$) and Hydrogen ($H_2$).
Question
What catalyst and promoter are used in the second step of the Bosch Process to reduce steam?
Answer
Iron (III) oxide ($Fe_2O_3$) is the catalyst, and chromic oxide ($Cr_2O_3$) is the promoter.
Question
How is Carbon dioxide ($CO_2$) removed from the product mixture in the Bosch Process?
Answer
By dissolving the mixture in water under high pressure ($30$ atmospheres) or in caustic potash solution.
Question
How is unreacted Carbon monoxide ($CO$) removed in the Bosch Process?
Answer
By dissolving the mixture in ammoniacal cuprous chloride solution.
Question
At which electrode is hydrogen gas liberated during the electrolysis of acidified water?
Answer
Hydrogen is liberated at the cathode.
Question
Describe the appearance and density of hydrogen gas relative to air.
Answer
It is a colourless, odourless, and tasteless gas that is $14.4$ times lighter than air.
Question
What observation is made when a burning splinter is brought near a jar of pure hydrogen?
Answer
The hydrogen burns quietly with a pale blue flame forming water.
Question
What sound is characteristic of hydrogen burning in the presence of air or oxygen?
Answer
A characteristic 'pop' sound.
Question
Why was hydrogen replaced by helium in meteorological balloons?
Answer
Because hydrogen is highly inflammable, whereas helium is non-flammable.
Question
In the manufacture of ammonia (Haber Process), what are the required temperature and pressure conditions?
Answer
Temperature of $450-500^\circ\text{C}$ and pressure of $200-900$ atmospheres.
Question
What is 'hydrogenation' of oil?
Answer
The addition of hydrogen to vegetable oils in the presence of a catalyst (like $Pt$ or $Ni$) to turn them into semi-solid fats.
Question
What is the phenomenon called when metals like platinum or palladium adsorb large volumes of hydrogen on their surface?
Answer
Occlusion.
Question
How does hydrogen act as a 'reducing agent' in metallurgy?
Answer
It reduces the heated oxides of less active metals (like $Zn$, $Fe$, $Cu$) to their metallic state.
Question
What type of flame, reaching temperatures around $2800^\circ\text{C}$, is used for welding and cutting metals?
Answer
Oxy-hydrogen flame.
Question
Define 'Oxidation' in terms of oxygen or hydrogen transfer.
Answer
Oxidation is the addition of oxygen to or the removal of hydrogen from a substance.
Question
Define 'Reduction' in terms of oxygen or hydrogen transfer.
Answer
Reduction is the removal of oxygen from or the addition of hydrogen to a substance.
Question
According to the electronic concept, what is 'Oxidation'?
Answer
Oxidation is the loss of one or more electrons from an atom or ion.
Question
According to the electronic concept, what is 'Reduction'?
Answer
Reduction is the gain of one or more electrons by an atom or ion.
Question
What is a 'Redox reaction'?
Answer
A chemical reaction involving simultaneous oxidation of one substance and reduction of another.
Question
In the reaction $2\text{Cu} + \text{O}_2 \rightarrow 2\text{CuO}$, which substance is oxidised?
Answer
Copper ($Cu$) is oxidised as it gains oxygen.
Question
In the reaction $\text{H}_2\text{S} + \text{Cl}_2 \rightarrow 2\text{HCl} + \text{S}$, which substance acts as the oxidising agent?
Answer
Chlorine ($\text{Cl}_2$) acts as the oxidising agent by removing hydrogen from $\text{H}_2\text{S}$.
Question
Define an 'Oxidising Agent' in terms of electron transfer.
Answer
An oxidising agent is an electron acceptor.
Question
Define a 'Reducing Agent' in terms of electron transfer.
Answer
A reducing agent is an electron donor.
Question
What change in valency occurs during Oxidation?
Answer
There is an increase in positive valency or a decrease in negative valency.
Question
What change in valency occurs during Reduction?
Answer
There is a decrease in positive valency or an increase in negative valency.
Question
Give one example of a liquid oxidising agent mentioned in the text.
Answer
Hydrogen peroxide ($H_2O_2$) or Concentrated Nitric acid ($HNO_3$).
Question
Give one example of a solid reducing agent mentioned in the text.
Answer
Carbon (coke) or active metals like Sodium ($Na$).
Question
How does an oxidising agent typically react with a colourless potassium iodide ($KI$) solution?
Answer
It liberates brown iodine, giving the solution a yellowish-brown colour.
Question
What is the effect of a reducing agent on acidified Potassium permanganate ($KMnO_4$) solution?
Answer
It turns the purple or pink solution colourless.
Question
What is the diatomic formula for Chlorine, and how many bonds link the two atoms?
Answer
The formula is $Cl_2$, and the atoms are linked by a single bond.
Question
In terms of electrovalency, how does Hydrogen react with metals like Sodium?
Answer
It forms electrovalent compounds like Sodium hydride ($NaH$).
Question
In terms of covalency, how does Hydrogen react with non-metals like Carbon?
Answer
It forms covalent compounds like Methane ($CH_4$).
Question
What is the percentage of hydrogen in the Earth's atmosphere?
Answer
Approximately $0.01\%$.
Question
Which metal is wrapped in wire gauze when reacting with cold water to prevent it from darting about and to collect hydrogen more easily?
Answer
Sodium ($Na$).