JAMB UTME - Chemistry - 2020

The most important element on the earth's crust is?

Maelezo ya Majibu

The most important element on Earth's crust is oxygen. Oxygen makes up about 46.6% of the Earth's crust by weight and is an essential component of many minerals and compounds that make up the Earth's crust. It also plays a critical role in supporting life on Earth, as it is necessary for respiration in most living organisms. Additionally, oxygen is involved in many geological processes, such as the weathering of rocks and the formation of soils. The abundance of oxygen in the Earth's crust and its importance to both geology and biology make it the most important element on the Earth's crust.

An example of a polysaccharide is?

Maelezo ya Majibu

Starch is an example of a polysaccharide. A polysaccharide is a type of carbohydrate made up of many simple sugar units linked together. Starch is one of the most common polysaccharides and is found in many foods, such as potatoes, rice, and bread. It is used as a source of energy for the body and is broken down into glucose, which can then be used by the cells for energy.

The substance often used for vulcanization of rubber is?

Maelezo ya Majibu

The substance often used for vulcanization of rubber is Sulphur. Vulcanization is a process that transforms rubber from a sticky, soft material into a strong, durable one. It's done by adding a small amount of sulphur to the rubber while heating it. The sulphur reacts with the rubber and creates chemical bonds within the rubber molecules, which results in a stronger and more stable material. This process makes the rubber more resistant to heat, abrasion, and other physical stresses, which makes it useful for a wide range of applications, such as tires, hoses, and gaskets.

Maelezo ya Majibu

Aluminum hydroxide is also used as a mordant in dyeing.

Deliquescent substances are also?

Maelezo ya Majibu

Deliquescent substances are hygroscopic, which means they have the ability to absorb moisture from the air. These substances dissolve in the absorbed moisture to form a solution. In other words, deliquescent substances become liquid when they absorb enough moisture from the air. This is in contrast to efflorescent substances, which lose moisture and become powdery, and anhydrous substances, which do not contain any water. Insoluble substances do not dissolve in a liquid, but deliquescent substances are soluble in the moisture they absorb from the air.

Which of the gas laws does this graph illustrate?

Maelezo ya Majibu

Charles' law describes the effect of temperature changes on the volume of a given mass of gas at a constant pressure.

When cathode rays are deflected onto the electrode of an electrometer, the instrument becomes?

Maelezo ya Majibu

When cathode rays are deflected onto the electrode of an electrometer, the instrument becomes negatively charged. This happens because cathode rays are made up of electrons, which are negatively charged particles. When these electrons collide with the electrode, they transfer their negative charge onto it, giving it a negative charge. In a very simple way, think of it like this: if you rub a balloon on your hair, the balloon will become negatively charged because it has gained electrons from your hair. Similarly, when cathode rays collide with the electrode of an electrometer, the electrode becomes negatively charged because it has gained electrons from the cathode rays.

Duralumin consists of aluminum, copper?

Maelezo ya Majibu

No, duralumin does not consist of aluminum and copper. Duralumin is an alloy made primarily of aluminum, with small amounts of copper, manganese, and sometimes a tiny amount of magnesium added. This combination of metals results in a material that is strong, lightweight, and resistant to corrosion.

A few drop of conc HCL are added to about 10cm${}^3$ of a solution of PH 3.4. The PH of the resulting mixture is

Maelezo ya Majibu

The pH of the resulting mixture will be less than 3.4. pH is a measure of the acidity or basicity of a solution and ranges from 0 to 14. A pH of 7 is neutral, a pH less than 7 is acidic, and a pH greater than 7 is basic. When a few drops of concentrated hydrochloric acid (HCl) are added to a solution with a pH of 3.4, the HCl will lower the pH of the solution. This is because HCl is a strong acid and will donate hydrogen ions (H+) to the solution, increasing the concentration of H+ ions and thus making the solution more acidic. The exact pH of the resulting mixture will depend on the amount of HCl added and the original concentration of the pH 3.4 solution.

When a solid substance disappears completely as a gas on heating, the substance is said to have undergone?

Maelezo ya Majibu

When a solid substance disappears completely as a gas on heating, the substance is said to have undergone sublimation. Sublimation is a process where a solid substance turns into a gas without first becoming a liquid. This occurs when the energy applied to the solid is enough to overcome the forces holding its particles together, causing it to transition directly into a gaseous state. Crystallization is the process by which a liquid solidifies into a crystalline solid, while distillation is a process used to separate mixtures of liquids based on their boiling points. Evaporation is the process by which a liquid turns into a gas at the surface of the liquid. These processes are different from sublimation and do not involve the solid disappearing completely as a gas upon heating.

If the quantity of oxygen occupying 2.76L container at a pressure of 0.825 atm and 300k is reduced by one-half, what is the pressure exerted by the remaining gas?

Maelezo ya Majibu

Using the combined gas law formula,

Given that P${}_1$ = 0.825,   V${}_1$ = 2.76 L, V${}_2$ = 1.38 L, P${}_2$ = ?

And T1 = T2; we would have P${}_2$ = [ P${}_1$ X V${}_1$ ] / V${}_2$

: [0.825 X 2.76] / 1.38

= 1.650atm

Maelezo ya Majibu

The general formula for Alkanals is RCHO, where R represents a hydrocarbon chain. Alkanals are a type of organic compounds that contain a carbonyl functional group (C=O) and a hydroxyl functional group (-OH). The formula for Alkanals is RCHO, where R represents a hydrocarbon chain. This means that the carbon atom in the carbonyl group is bonded to a hydrogen atom and a carbon chain. The carbon chain can be a straight-chain or a branched-chain hydrocarbon. It is important to note that Alkanals are different from other organic compounds such as Alkanes, Alkenes, and Alkynes, which have different chemical and physical properties.

The electronic configuration of an element is 1S${}^2$ 2S${}^2$ 2P${}^6$ 3S${}^2$ 3P${}^3$. How many unpaired electrons are there in the element?

Maelezo ya Majibu

Once you figure out the electron configuration, you fill up the corresponding orbitals with electrons, any left with one is considered unpaired. Since 1s can only hold 2 electrons, and P has 15, that's obviously filled and has no unpaired electrons. The same is for 2s which holds 2, 2p which holds 6, 3s which holds 2.However 3p can hold 6 electrons and in order for that to be filled up you would need to have an element of 18 electrons. So you fill up as much as you can in 3p by first adding 1 electron to each energy level. 3p has 3 energy levels and there are only 3 electrons left to distribute, so each of those energy levels only gets 1, because you have to fill them all with one before you can start adding a second.So since you are only able to fill one electron in each of the three energy levels of the 3p orbital, that leaves the orbital open for 1 more electron in each of its energy levels. So there are 3 unpaired electrons in P.

When water drops are added to calcium carbide in a container and the gas produced is passed through a jet and lighted, the resultant flame is called an?

Maelezo ya Majibu

When water is added to calcium carbide, it produces acetylene gas. When this gas is passed through a jet and lighted, the flame produced is called an "Oxyacetylene flame". This flame is hot and is used in welding and cutting metal.

Liquid black soap is made by boiling palm oil with liquid extract of ash. The function of the ash is to provide the ?

Maelezo ya Majibu

The function of the ash in liquid black soap is to provide an alkali. Alkalis are substances that have a high pH and can neutralize acids. In the case of liquid black soap, the ash is usually made from the ashes of plant material, such as wood or plantain skins, and is a source of potassium hydroxide (KOH), a strong alkali. When the ash is combined with the palm oil and heated, it reacts with the oils in the palm oil to form soap. The soap is formed through a process called saponification, which is the reaction between an alkali and a fat or oil to form soap and glycerol. In this way, the ash acts as an essential ingredient in the soap-making process, providing the alkali necessary for the formation of soap.

The number of molecules of Carbon(iv)Oxide produced when 10.0g of CaCO${}_3$ is treated with 0.2dm${}^3$ of 1 Mole of HCL in the equation

CaCO${}_3$ + 2HCL $?$ CaCl${}_2$  + H${}_2$ O + CO${}_2$  , is ?

Maelezo ya Majibu

To obtain pure carbon(ii)oxide from its mixture with carbon(iv)oxide, the mixture should be?

Maelezo ya Majibu

carbon(ii)oxide is prepared from carbon(iv)oxide by passing the latter through red-hot carbon and the unchanged CO${}_2$ is removed when the mixture of the gases through conc NAOH.

Which of the following can be obtained by fractional distillation? 

Maelezo ya Majibu

Fractional distillation is used to separate mixtures into its component parts or fractions with the difference in boiling points between successive fractions must be more than 10°C. An example is the liquid nitrogen and oxygen are then separated by fractional distillation .

The shape of ammonia molecule is?

Maelezo ya Majibu

The ammonia molecule has a trigonal pyramidal shape with the three hydrogen atoms and an unshared pair of electrons attached to the nitrogen atom.

Which of the following substances is a mixture?

Maelezo ya Majibu

Granulated sugar and seawater are mixtures while sodium chloride and iron filings are pure substances. A mixture is a combination of two or more substances in which each substance retains its own chemical properties and can be separated from the mixture by physical means. Granulated sugar is a mixture of two or more types of sugar crystals. Seawater is a mixture of water, salt, and other minerals. A pure substance, on the other hand, has a fixed chemical composition and distinct chemical and physical properties. Sodium chloride is a pure substance because it is made up of only sodium and chloride ions and has a fixed chemical composition. Iron filings are also a pure substance because they are made up of only iron atoms and have a fixed chemical composition.

An organic compound that does not undergo a reaction with both hydrogen cyanide and hydroxylamine can be?

Maelezo ya Majibu

Organic compounds are compounds that contain carbon and hydrogen, and can also contain other elements like oxygen, nitrogen, and chlorine. In organic chemistry, the reaction of a compound with hydrogen cyanide (HCN) or hydroxylamine (NH2OH) can provide information about the functional group present in the compound. An organic compound that does not undergo a reaction with both hydrogen cyanide and hydroxylamine can be an alkene. Alkenes are organic compounds that contain a carbon-carbon double bond, and they do not react with either hydrogen cyanide or hydroxylamine. On the other hand, alkanals, alkanones, and alkanoic acids are functional groups that do react with hydrogen cyanide or hydroxylamine, so they are not the organic compounds that do not undergo a reaction with both hydrogen cyanide and hydroxylamine.

Four elements P, Q, R and S have atomic numbers of 4, 10, 12 and 14 respectively. Which of these elements is noble gas? 

Maelezo ya Majibu

They are the most stable due to having the maximum number of valence electrons their outer shell can hold. Therefore, they rarely react with other elements since they are already stable.

What mass of water is produced when 8.0g of hydrogen reacts with excess oxygen?

Maelezo ya Majibu

2H${}_2$ + O${}_2$ $\to$ 2H${}_2$O
From the equation:4g of Hydrogen produces 36g of water: 8g of Hydrogen will produce 72g of water

How many valence electrons are contained in the element ${}_{15}^{31}P$?

Maelezo ya Majibu

The element is Phosphorus in group 5 with valencies of 3 and 5.

32g of anhydrous copper(ii)tetraoxosulphate(vi) dissolved in 1dm${}^3$ of water generated 13.0kj of heat. The heat solution is?

Maelezo ya Majibu

32g of CUSO${}_4$ liberate 13.0kj of heatMolar mass of CUSO${}_4$ = 160gNo. of moles of CUSO${}_4$  = 32gNo. of moles = 32(mass) / 160(molar mass)= 0.2 molesi.e 0.2 = 13kj1 moles = xkj: 65KJ 

8g of CH${}_4$ occupies 11.2 at S.T.P. What volume would 22g of CH${}_3$CH${}_2$CH${}_3$ occupy under the same condition?

Maelezo ya Majibu

The volume occupied by a certain amount of a gas at Standard Temperature and Pressure (S.T.P) can be calculated using the Ideal Gas Law, which states that PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the gas constant, and T is the temperature. Since the temperature and pressure are constant at S.T.P, we can use the following formula to calculate the volume occupied by a certain amount of gas: V = nRT/P, where n is the number of moles of the gas. So, if 8g of CH4 occupy 11.2 dm3 at S.T.P, then we can calculate the number of moles of CH4 using the molar mass of CH4 (16 g/mol) as follows: n = 8g / 16 g/mol = 0.5 mol And the volume occupied by 0.5 mol of CH4 at S.T.P can be calculated as follows: V = nRT/P = 0.5 * 8.31 * 273 / 101.3 = 11.2 dm3 Using the same approach, we can calculate the volume occupied by 22g of CH3CH2CH3 at S.T.P as follows: n = 22g / (3 * 12 + 6 * 1 + 3 * 16) g/mol = 0.5 mol V = nRT/P = 0.5 * 8.31 * 273 / 101.3 = 11.2 dm3 Therefore, 22g of CH3CH2CH3 would occupy 11.2 dm3 at S.T.P.

What process would coal undergo to give coal gas, coal tar, ammoniacal liquor and coke?

Maelezo ya Majibu

Coal undergoes a process called destructive distillation to give coal gas, coal tar, ammoniacal liquor, and coke. Destructive distillation is a process where coal is heated in the absence of air to produce a mixture of gases, liquids, and solids. The process takes advantage of the differences in boiling points between the various components of coal to separate them. During the process, coal is heated in a closed retort (a type of oven) to temperatures ranging from 500°C to 900°C. This causes the coal to decompose into a mixture of gases, liquids, and solids. The gases produced, including methane, hydrogen, and carbon monoxide, are known as coal gas. The liquids produced, including benzene, toluene, and naphthalene, are known as coal tar. The ammoniacal liquor is produced by the reaction of coal tar with ammonia, while the solid residue is called coke. The resulting products have different uses, such as coal gas for heating and cooking, coal tar for making chemicals, ammoniacal liquor for making fertilizers, and coke for use in iron and steel production.

The chlorinated alkane often used industrially to remove grease is?

Maelezo ya Majibu

The chlorinated alkane often used industrially to remove grease is Trichloromethane, also known as chloroform. Chloroform is a solvent, which means it is a liquid that can dissolve grease and other substances. It's used in industrial cleaning and degreasing processes because it's effective at removing grease and oil from surfaces. Additionally, it evaporates quickly, leaving behind a clean surface. However, it's important to note that chloroform is a toxic substance and should only be used with proper protective measures in place.

Chromatography is used to separate components of mixture which differ in their rates of ?

Maelezo ya Majibu

Chromatography is used to separate components of a mixture based on their migration or movement through a stationary phase, such as a solid or a liquid, and a mobile phase, such as a gas or a liquid. The components in the mixture have different rates of migration, so they will separate as they move through the stationary phase, allowing us to identify and isolate each component. This is because each component has a unique combination of physical and chemical properties that affect how it moves through the stationary phase and the mobile phase. The process of chromatography can be compared to a race, where the components in the mixture are like runners and the stationary and mobile phases are like a track. Just like runners move at different speeds on a track, the components in the mixture will move at different rates through the stationary and mobile phases, leading to separation.

The products of the thermal decomposition of ammonium trioxonitrate(v) are?

Maelezo ya Majibu

NH${}_4$NO${}_3$ Ammonium Trioxonitrate(V) , unlike all other metallic trioxonitrates(v), decomposes on heating to give nitrogen(i)oxide N${}_2$O and water.

Which of the following gases will rekindle a brightly splint?

Maelezo ya Majibu

Nitrogen(I)Oxide rekindles a brightly glowing splinter but extinguishes a feebly glowing one which is not hot enough to decompose the gas to liberate oxygen

The volume occupied by 1.58g of a gas at S.T.P is 500cm${}^3$. What is the relative molecular mass of the gas?  [ G.M.V at S.T.P = 22.4dm${}^3$ ]

Maelezo ya Majibu

500cm3 of the gas weighed 1.58
: 22400cm3 of the gas weight
[22400 X 1.58g] ÷ [ 500 ]
= 71

Proteins in acid solution undergo?

Maelezo ya Majibu

Proteins in acid solution undergo hydrolysis. This means that the protein molecule is broken down into smaller pieces by a chemical reaction with water. In an acid solution, the acid acts as a catalyst to increase the rate of this reaction, leading to the breakdown of the protein into smaller peptides and amino acids. This process is important in many biological processes, such as digestion, where proteins are broken down into smaller components that can be absorbed and used by the body. Hydrolysis can also be used to analyze proteins in the laboratory, by breaking down the protein into smaller pieces that can be studied and identified. In a simple way, hydrolysis can be thought of as a process that cuts up a large protein into smaller pieces, like cutting a rope into smaller sections.

What are the possible oxidation numbers of an element if its atomic number is 17?

Maelezo ya Majibu

The oxidation number of an element is a number that represents the charge of an atom in a chemical compound. The oxidation number of an element can be determined by following a set of rules. Here are a few rules to help determine the oxidation number of an element: - The oxidation number of a pure element is always 0. - The oxidation number of a monatomic ion is equal to its charge. - In a neutral compound, the sum of the oxidation numbers of all elements is 0. - The oxidation number of oxygen is usually -2, unless it is part of a peroxide or in a superoxide, where it is -1. - The oxidation number of hydrogen is usually +1, except in metal hydrides where it is -1. Using these rules, we can determine the possible oxidation numbers of chlorine (element with atomic number 17). Chlorine can have an oxidation number of -1 or +7. This is because chlorine typically has an oxidation number of -1 in compounds like chloride ions (Cl-) and an oxidation number of +7 in compounds like chlorine gas (Cl2). Therefore, the possible oxidation numbers of chlorine are -1 and +7.

What quantity of electricity will liberate 0.125 mole of oxygen molecules during the electrolysis of dilute sodium chloride solution?

Maelezo ya Majibu

4OH ⇒ 2H${}_2$O + O${}_2$ + 4e-

From the equation:

1 mole of Oxygen requires 4e 

i.e 1 mole of Oxygen requires 4F,

where 1F = 96,500 C

[ 4 X 96,500 X 0.125 ] ÷ 1

= 48,250 C

A gaseous metallic chloride MCl consists of 20.22% of M by mass. The formula of the chloride is?

[ M = 27, Cl = 35.5]

Maelezo ya Majibu

Explanation:

Which of the following types of bonding does not involve the formation of new substances?

Maelezo ya Majibu

Helium is used in observation of ballons because it is?

Maelezo ya Majibu

Helium is used in balloons because it is light and non-combustible. Helium is a gas that is much lighter than air, which means that when it is filled inside a balloon, the balloon rises up into the air. This makes it ideal for use in observation balloons, as it allows the balloons to float and stay aloft for extended periods of time. In addition, helium is non-combustible, which means that it does not catch fire or ignite easily. This makes it a safe choice for use in balloons, as it eliminates the risk of fire or explosion that can be caused by other, more flammable gases. Overall, the combination of being light and non-combustible makes helium a popular choice for use in balloons, as it provides a safe and effective way to keep the balloons aloft.

An electron can be added to a halogen atom to form a halide ion with?

Maelezo ya Majibu

A halide ion is a halogen atom bearing a negative charge (which is an anion with a charge of -1). The halide anions are fluoride (F${}^{-}$), chloride (Cl${}^{-}$), bromide (Br${}^{-}$), iodide (I${}^{-}$) and astatide (At${}^{-}$).

The best treatment for a student who accidentally poured conc tetraoxosulphate(vi) on his skin in the laboratory is to wash his skin with?

Maelezo ya Majibu

The best treatment for a student who accidentally poured copper sulfate on their skin in the laboratory is to wash the affected area with cool running water. This is because copper sulfate is an irritant that can cause skin irritation and potentially cause harm if left on the skin for too long. Washing the skin with cool water will help to remove the chemical and reduce the risk of further irritation or harm. It is important to avoid using sodium hydroxide solution, iodine solution, or sodium trioxonitrate(v) solution as these chemicals may cause further irritation or harm to the skin and should not be used without professional medical guidance.