Chemistry Mock Paper PDF

Chemistry Mock Paper: 1.) Describe the properties of the sub atomic particles and their arrangement in the atom ( 8 marks) Protons - Have a positive charge - 1 atomic mass - Found in nucleus - Determines atomic number and identity of element Neutrons - Has no charge - Approxima...

Chemistry Mock Paper: 1.) Describe the properties of the sub atomic particles and their arrangement in the atom ( 8 marks) Protons - Have a positive charge - 1 atomic mass - Found in nucleus - Determines atomic number and identity of element Neutrons - Has no charge - Approximately 1 amu - Found in nucleus - Helps to stabilize electrons Electrons - Negative charge --1 - Lighter mass lighter than protons and neutrons - Found in orbitals around nucleus - Involved in chemical bonding and reactions 2.) What shell is the valence shell of calcium? What is the electron configuration of this shell? ( 8 marks) Valence shell of calcium is 20. Calcium has atomic number of 20 so electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² And **valence shell** is the **4th shell** (n = 4) with the electron configuration **4s²**. 3.) Discuss the process of ester formation via equation formula, number few physical properties, give an example of biologically important ester? ( 8 marks) Ester formation (also known as esterification) occurs when a carboxylic acid reacts with an alcohol, typically in the presence of an acid catalyst. ### **Physical Properties of Esters:** - **Smell**: Pleasant, often fruity. - **Boiling Point**: Lower than acids/alcohols. - **Solubility**: Soluble in organic solvents, less soluble in water. **Reaction**: A carboxylic acid reacts with an alcohol, usually with an acid catalyst. - **General formula**: - **RCOOH + R\'OH → RCOOR\' + H₂O** - Example: **Ethanoic acid (CH₃COOH)** + **Ethanol (C₂H₅OH)** → **Ethyl acetate (CH₃COOC₂H₅)** + **Water**. **Biologically Important Ester:** - **Triglycerides** (fats and oils) are esters formed from **glycerol** and **fatty acids** 4.) Explain how electrons are distributed in covalent bonds? Electrons are shared between atoms to achiebe stable electron configuration. - Each atom contributes one or more electrons to the bond, forming a pair of electrons that are shared between the atoms. - For example, in a **H₂ molecule**, each hydrogen atom shares its single electron with another hydrogen atom, forming a single covalent bond. 5.) Explain hydrogen bond formation and the circumstances when it occurs provide an example of a molecule that can act as both hydrogen bond donor and hydrogen bond acceptor? ( 8 marks) - **Hydrogen bond formation** occurs when a hydrogen atom is covalently bonded to a highly electronegative atom (like oxygen, nitrogen, or fluorine), and the hydrogen is attracted to a lone pair of electrons on another electronegative atom. - **Conditions**: Hydrogen bonding occurs when hydrogen is bonded to electronegative atoms such as **O**, **N**, or **F**, creating a partially positive charge on hydrogen that is attracted to a partially negative charge on another electronegative atom. - **Example of a molecule**: **Water (H₂O)** can act as both a **hydrogen bond donor** (through the hydrogen atoms) and an **acceptor** (through the lone pairs of electrons on oxygen). 6.) Most organic compounds are organised into families defined by functional groups. Write condensed formula for 7 organic compounds containing R=CH3 and highlight their functional groups? ( 8 marks) Here are 7 examples of organic compounds containing **R = CH₃** (methyl group): 1. **Methanol (CH₃OH)**: Alcohol (-OH group). 2. **Methylamine (CH₃NH₂)**: Amine (-NH₂ group). 3. **Acetone (CH₃COCH₃)**: Ketone (C=O group). 4. **Methyl chloride (CH₃Cl)**: Alkyl halide (C-Cl group). 5. **Methyl ethanoate (CH₃COOCH₃)**: Ester (-COO group). 6. **Toluene (C₆H₅CH₃)**: Aromatic compound (benzene ring). 7. **Methylbutane (CH₃CH₂CH₂CH₃)**: Alkane (C-H and C-C bonds). ?????????????????????????????????????????????????????????????????????? 7.) Which one of the following carries a positive charge ( 4 marks) a.) Nucleus b.) Proton c.) Neutron d.) Electron e.) Atom 8.) How many moles are there in 30g of C? ( 4 marks) Moles = mass/molar mass = 30/12 = 2.5mol a.) 360 mol b.) 30 mol c.) 2.5 mol d.) 0.4 mol e.) 12 mol 9.) The identity of a chemical element is determined by which of the following? ( 4 marks) a.) The number of protons it possesses b.) The number of neutrons it possesses c.) The number of electrons it possesses d.) The sum of the number of protons and neutrons it possesses e.) The sum of the number of protons and electrons it possesses 10.) Which of the following reactions depict the behavior of a base? ( 4 marks) = A base is a substance that can accept a proton (H+). Let\'s analyze each reaction: **A) NH3 + H+ ⇌ NH4+** In this reaction, NH3 (ammonia) accepts a proton from H+, forming NH4+ (ammonium ion). Therefore, **NH3 acts as a base** in this reaction. **B) CH3COO- + H+ ⇌ CH3COOH** Here, CH3COO- (acetate ion) accepts a proton from H+, forming CH3COOH (acetic acid). So, **CH3COO- acts as a base** as well. **C) CH3COOH ⇌ CH3COO- + H+** In this reaction, CH3COOH (acetic acid) donates a proton (H+) to form CH3COO- (acetate ion). Therefore, **CH3COOH acts as an acid** in this reaction. **D) H2O ⇌ H2 + O2-** This reaction is not common and doesn\'t represent a typical acid-base reaction. **E) H2O + H+ ⇌ H3O+** Here, H2O (water) accepts a proton from H+, forming H3O+ (hydronium ion). So, **H2O acts as a base** in this reaction. Therefore, the reactions that depict the behavior of a base are **A, B, and E**. 11.) What is the mass of 1.5 mol CH3OH ( 4 marks) a.) 48g b.) 21.33g c.) 32g d.) 0.05g e.) 1.5g Molar mass of CH3OH Carbon= 12 Hydrogen = 1 but there is 4 so times by 4 = 4 Oxygen = 16 Total = 32 1.5 x 32= 48g 12.) Which is the correct electron configuration of oxygen ( 4 marks) 13.) The 2p sub shell contains how many orbitals ( 4 marks) a.) one b.) two c.) three d.) four e.) five 14.) Which of the following bonds is most strongly polarized ( 4 marks) a.) C-H b.) C=O c.) N-H d.) C-N e.) C=S 15.) Which one of the following compounds contains ethyl group ( 4 marks) =Looking at the options: - **A)** This molecule has a methyl group (-CH3) attached to a double bond. - **B)** This molecule has two carbon atoms connected by a single bond. There is no ethyl group present. - **C)** This molecule has a chain of carbon atoms, but the longest chain is a pentyl group (5 carbons). Therefore, **none** of the given compounds contains an ethyl group. 16.) Which one of the following compounds has the highest boiling point ( 4 marks) a.) methane b.) ethane c.) ethanoic acid d.) dimethyl ether e.) propane 1. The boiling point of a compound is influenced by the strength of its intermolecular forces (e.g., hydrogen bonding, dipole-dipole interactions, or Van der Waals forces). 2. **Methane (CH₄)** and **ethane (C₂H₆)** are nonpolar molecules with weak London dispersion forces. 3. **Dimethyl ether (CH₃OCH₃)** has dipole-dipole interactions but no hydrogen bonding. 4. **Ethanoic acid (CH₃COOH)** has hydrogen bonding, which significantly increases its boiling point compared to the other compounds. 17.) A buffer solution is composed of which of the following ( 4 marks) a.) a weak acid in solution b.) a strong acid in solution c.) a weak base in solution d.) a weak acid and conjugate base in solution e.) a strong acid and conjugate base in solution 18.) The following reaction mechanism is a type of which of the following ( 4 marks) a.) substitution b.) addition c.) condensation d.) elimination e.) hydrolysis The answer is **a.) substitution**. As explained previously, the reaction mechanism shown involves the replacement of one group (X) with another (Y) in a molecule, which is the characteristic of a substitution reaction. Here\'s a brief overview of the other options: - **Addition:** Involves adding atoms or groups to a molecule, typically across a double or triple bond. - **Condensation:** Involves combining two molecules with the elimination of a small molecule, such as water. - **Elimination:** Involves removing atoms or groups from a molecule, often resulting in the formation of a double bond. - **Hydrolysis:** Involves breaking a bond using water. None of these other options fit the given reaction mechanism. 19.) How many pairs of structural isomers are there here? a.) none b.)1 c.)2 d.)3 e.)4 = To determine the number of pairs of structural isomers in the given image, we need to identify molecules with the same molecular formula but different connectivity of atoms. Here are the pairs of structural isomers I can identify from the image: 1. **Pair 1:** a. **Molecule 1:** The first molecule on the left, with the -OH group on the second carbon. b. **Molecule 2:** The second molecule from the left, with the -OH group on the first carbon. 2. **Pair 2:** c. **Molecule 1:** The third molecule from the left, with a double bond between the first and second carbons. d. **Molecule 2:** The fourth molecule from the left, with a double bond between the second and third carbons. Therefore, there are **2 pairs of structural isomers** present in the given image.